* [PATCHSET v2 sched_ext/for-7.4] sched_ext: Add lazy preemption support
@ 2026-09-14 8:47 Andrea Righi
2026-09-14 8:47 ` [PATCH 1/2] " Andrea Righi
2026-09-14 8:47 ` [PATCH 2/2] selftests/sched_ext: Add lazy preemption tests Andrea Righi
0 siblings, 2 replies; 8+ messages in thread
From: Andrea Righi @ 2026-09-14 8:47 UTC (permalink / raw)
To: Tejun Heo, David Vernet, Changwoo Min
Cc: Emil Tsalapatis, sched-ext, linux-kernel
The fair scheduling class can defer a scheduling boundary through lazy
rescheduling, but sched_ext currently exposes only immediate preemption to BPF
schedulers.
This series adds lazy variants of the enqueue and kick preemption flags. They
expire the running sched_ext task's slice while allowing the scheduling boundary
to be deferred until a return to user space or the next scheduler tick.
SCX_OPS_LAZY_SLICE_EXPIRY selects lazy slice expiry by default. Schedulers can
override that default in either direction for individual tasks through
scx_bpf_task_set_slice_expiry(). The helper preserves sub-scheduler task
ownership boundaries. Bypass continues to force immediate rescheduling.
Lazy enqueue and kick requests also restore the scheduler tick when targeting an
infinite-slice task on a NO_HZ_FULL CPU, ensuring forward progress even when the
target's tick has stopped.
The kselftests cover immediate and lazy preemption, coalescing and precedence
between kick modes, enqueue preemption, per-task slice-expiry overrides, invalid
flags and lazy preemption of infinite-slice tasks on NO_HZ_FULL CPUs.
Tested in separate virtme-ng runs, covering preempt=lazy and nohz_full:
$ vng -a "preempt=lazy" -- tools/testing/selftests/sched_ext/runner -t kick
$ vng -a "preempt=lazy nohz_full=8-15" -- tools/testing/selftests/sched_ext/runner -t nohz_tick
kick:
PASSED: 6
SKIPPED: 0
FAILED: 0
nohz_tick:
CPU 8 received 7 finite-slice ticks
PASSED: 1
SKIPPED: 0
FAILED: 0
Changes in v2:
- Make lazy slice expiry a per-task property (Tejun Heo).
- Add scx_bpf_task_set_slice_expiry() for per-task overrides from any sched_ext
callback (preserving sub-scheduler task ownership).
- Restore the scheduler tick dependency for lazy enqueue and kick preemption of
infinite-slice tasks on NO_HZ_FULL CPUs (Tejun Heo).
- Accumulate immediate and lazy kick requests independently and resolve their
precedence in kick_one_cpu() (Tejun Heo).
- Allow PREEMPT|PREEMPT_LAZY and WAIT|PREEMPT_LAZY, immediate preemption, WAIT
and plain kicks take precedence over lazy preemption (Tejun Heo).
- Clear both preemption masks together when processing or skipping a preemption
request (Tejun Heo).
- Extend the kselftests with combined and ordered kick requests, per-task
expiry overrides and NO_HZ_FULL coverage.
- Link to v1: https://lore.kernel.org/r/20260911195800.974364-1-arighi@nvidia.com
Andrea Righi (2):
sched_ext: Add lazy preemption support
selftests/sched_ext: Add lazy preemption tests
include/linux/sched/ext.h | 8 +
kernel/sched/ext/ext.c | 146 +++++-
kernel/sched/ext/internal.h | 39 +-
kernel/sched/ext/sub.c | 15 +-
tools/sched_ext/include/scx/compat.bpf.h | 13 +
tools/sched_ext/include/scx/enum_defs.autogen.h | 3 +
tools/sched_ext/include/scx/enums.autogen.bpf.h | 6 +
tools/sched_ext/include/scx/enums.autogen.h | 2 +
tools/sched_ext/include/scx/enums_abi.autogen.h | 5 +-
tools/testing/selftests/sched_ext/Makefile | 1 +
tools/testing/selftests/sched_ext/kick.bpf.c | 166 +++++++
tools/testing/selftests/sched_ext/kick.c | 526 ++++++++++++++++++++++
tools/testing/selftests/sched_ext/nohz_tick.bpf.c | 54 ++-
tools/testing/selftests/sched_ext/nohz_tick.c | 189 +++++++-
14 files changed, 1129 insertions(+), 44 deletions(-)
^ permalink raw reply [flat|nested] 8+ messages in thread
* [PATCH 1/2] sched_ext: Add lazy preemption support
2026-09-14 8:47 [PATCHSET v2 sched_ext/for-7.4] sched_ext: Add lazy preemption support Andrea Righi
@ 2026-09-14 8:47 ` Andrea Righi
2026-09-14 8:47 ` [PATCH 2/2] selftests/sched_ext: Add lazy preemption tests Andrea Righi
1 sibling, 0 replies; 8+ messages in thread
From: Andrea Righi @ 2026-09-14 8:47 UTC (permalink / raw)
To: Tejun Heo, David Vernet, Changwoo Min
Cc: Emil Tsalapatis, sched-ext, linux-kernel
The fair scheduling class can request lazy rescheduling, deferring an
in-kernel scheduling boundary until returning to user space or until the
next scheduler tick. sched_ext only exposes immediate preemption,
preventing BPF schedulers from making the same trade-off.
Add SCX_ENQ_PREEMPT_LAZY and SCX_KICK_PREEMPT_LAZY. Both expire the
current sched_ext task slice but request lazy rescheduling. Immediate
preemption, WAIT and plain kicks take precedence when requests are
combined, while a lazy enqueue to a non-local DSQ retains the
head-insertion semantics of SCX_ENQ_PREEMPT.
Add SCX_OPS_LAZY_SLICE_EXPIRY as the default expiry policy for newly
enabled tasks and initialize it before ops.enable(). Add
scx_bpf_task_set_slice_expiry() so the owning scheduler can override the
policy per task from any callback while preserving sub-scheduler task
ownership boundaries. Bypass continues to force immediate expiry.
Restore the scheduler tick dependency before lazily rescheduling a task
whose infinite slice allowed a NO_HZ_FULL CPU to stop its tick.
Accumulate kick requests independently and resolve precedence while
holding the target rq lock. Reject unknown kick flags and invalid
SCX_KICK_IDLE combinations.
Signed-off-by: Andrea Righi <arighi@nvidia.com>
---
include/linux/sched/ext.h | 8 +
kernel/sched/ext/ext.c | 146 +++++++++++++++---
kernel/sched/ext/internal.h | 39 ++++-
kernel/sched/ext/sub.c | 15 +-
tools/sched_ext/include/scx/compat.bpf.h | 13 ++
.../sched_ext/include/scx/enum_defs.autogen.h | 3 +
.../sched_ext/include/scx/enums.autogen.bpf.h | 6 +
tools/sched_ext/include/scx/enums.autogen.h | 2 +
.../sched_ext/include/scx/enums_abi.autogen.h | 5 +-
9 files changed, 200 insertions(+), 37 deletions(-)
diff --git a/include/linux/sched/ext.h b/include/linux/sched/ext.h
index 8de69843c2150..685f1846aa386 100644
--- a/include/linux/sched/ext.h
+++ b/include/linux/sched/ext.h
@@ -249,6 +249,14 @@ struct sched_ext_entity {
*/
u64 dsq_vtime;
+ /*
+ * If set, depletion of this task's slice at the scheduler tick requests
+ * lazy instead of immediate rescheduling. Initialized from
+ * %SCX_OPS_LAZY_SLICE_EXPIRY immediately before ops.enable() and may be
+ * modified afterwards with scx_bpf_task_set_slice_expiry().
+ */
+ bool slice_expires_lazy;
+
/*
* Out-of-band slice request from scx_bpf_task_set_slice() when the
* caller does not hold the rq lock, applied under the rq lock at the
diff --git a/kernel/sched/ext/ext.c b/kernel/sched/ext/ext.c
index 4080902a528cd..09fed46cae0df 100644
--- a/kernel/sched/ext/ext.c
+++ b/kernel/sched/ext/ext.c
@@ -383,11 +383,11 @@ static bool rq_is_open(struct rq *rq, u64 enq_flags)
return true;
/*
- * %SCX_ENQ_PREEMPT clears $curr's slice if on SCX and kicks dispatch,
- * so allow it to avoid spuriously triggering reenq on a combined
+ * The preemption flags clear $curr's slice if on SCX and kick dispatch,
+ * so allow them to avoid spuriously triggering reenq on a combined
* PREEMPT|IMMED insertion.
*/
- if (enq_flags & SCX_ENQ_PREEMPT) {
+ if (enq_flags & (SCX_ENQ_PREEMPT | SCX_ENQ_PREEMPT_LAZY)) {
struct task_struct *curr = rq->curr;
/*
@@ -1515,6 +1515,23 @@ static void call_task_dequeue(struct scx_sched *sch, struct rq *rq,
p->scx.flags &= ~SCX_TASK_IN_CUSTODY;
}
+/*
+ * A task with an infinite slice may be running with its tick stopped. Lazy
+ * rescheduling doesn't send an IPI, so restore the tick dependency first to
+ * guarantee that the lazy request is promoted by a real scheduler tick.
+ */
+static void scx_resched_curr_lazy(struct rq *rq)
+{
+ if (rq->scx.flags & SCX_RQ_CAN_STOP_TICK) {
+ rq->scx.flags &= ~SCX_RQ_CAN_STOP_TICK;
+ update_rq_clock(rq);
+ update_other_load_avgs(rq);
+ sched_update_tick_dependency(rq);
+ }
+
+ resched_curr_lazy(rq);
+}
+
static void rq_owned_post_enq(struct scx_sched *sch, struct rq *rq,
struct scx_dispatch_q *dsq, struct task_struct *p,
u64 enq_flags)
@@ -1577,12 +1594,16 @@ static void rq_owned_post_enq(struct scx_sched *sch, struct rq *rq,
if (rq->scx.flags & SCX_RQ_IN_DISPATCH)
return;
- if ((enq_flags & SCX_ENQ_PREEMPT) && p != rq->curr &&
+ if ((enq_flags & (SCX_ENQ_PREEMPT | SCX_ENQ_PREEMPT_LAZY)) && p != rq->curr &&
rq->curr->sched_class == &ext_sched_class) {
- if (likely(scx_set_task_slice(rq->curr, 0)))
- resched_curr(rq);
- else
+ if (likely(scx_set_task_slice(rq->curr, 0))) {
+ if (enq_flags & SCX_ENQ_PREEMPT)
+ resched_curr(rq);
+ else
+ scx_resched_curr_lazy(rq);
+ } else {
__scx_add_event(sch, SCX_EV_SLICE_DENIED, 1);
+ }
}
}
@@ -1672,7 +1693,7 @@ static void scx_dispatch_enqueue(struct scx_sched *sch, struct rq *rq,
scx_error(sch, "DSQ ID 0x%016llx already had PRIQ-enqueued tasks",
dsq->id);
- if (enq_flags & (SCX_ENQ_HEAD | SCX_ENQ_PREEMPT)) {
+ if (enq_flags & (SCX_ENQ_HEAD | SCX_ENQ_PREEMPT | SCX_ENQ_PREEMPT_LAZY)) {
/* new task inserted at head - use fastpath */
if (dsq_insert_head(dsq, p) && !(dsq->id & SCX_DSQ_FLAG_BUILTIN))
rcu_assign_pointer(dsq->first_task, p);
@@ -2386,7 +2407,7 @@ void scx_move_local_task_to_local_dsq(struct scx_sched *sch, struct task_struct
WARN_ON_ONCE(p->scx.holding_cpu >= 0);
- if (enq_flags & (SCX_ENQ_HEAD | SCX_ENQ_PREEMPT))
+ if (enq_flags & (SCX_ENQ_HEAD | SCX_ENQ_PREEMPT | SCX_ENQ_PREEMPT_LAZY))
dsq_insert_head(dst_dsq, p);
else
list_add_tail(&p->scx.dsq_list.node, &dst_dsq->list);
@@ -3804,8 +3825,14 @@ static void task_tick_scx(struct rq *rq, struct task_struct *curr, int queued)
else if (SCX_HAS_OP(sch, tick))
SCX_CALL_OP_TASK(sch, tick, rq, curr);
- if (!curr->scx.slice)
- resched_curr(rq);
+ if (!curr->scx.slice) {
+ /* the slice can't be trusted while bypassing */
+ if (READ_ONCE(curr->scx.slice_expires_lazy) &&
+ !scx_bypassing(sch, cpu_of(rq)))
+ resched_curr_lazy(rq);
+ else
+ resched_curr(rq);
+ }
}
#ifdef CONFIG_EXT_GROUP_SCHED
@@ -3921,6 +3948,7 @@ static void __scx_enable_task(struct scx_sched *sch, struct task_struct *p)
weight = sched_prio_to_weight[p->static_prio - MAX_RT_PRIO];
p->scx.weight = sched_weight_to_cgroup(weight);
+ p->scx.slice_expires_lazy = sch->ops.flags & SCX_OPS_LAZY_SLICE_EXPIRY;
if (SCX_HAS_OP(sch, enable))
SCX_CALL_OP_TASK(sch, enable, rq, p);
@@ -5371,6 +5399,7 @@ static void scx_sched_free_rcu_work(struct work_struct *work)
free_cpumask_var(pcpu->cpus_to_kick);
free_cpumask_var(pcpu->cpus_to_kick_if_idle);
free_cpumask_var(pcpu->cpus_to_preempt);
+ free_cpumask_var(pcpu->cpus_to_preempt_lazy);
free_cpumask_var(pcpu->cpus_to_wait);
exit_dsq(scx_bypass_dsq(sch, cpu));
@@ -6883,6 +6912,9 @@ static void scx_dump_cpu(struct scx_sched *sch, struct seq_buf *s,
if (!cpumask_empty(pcpu->cpus_to_preempt))
scx_dump_line(&ns, " cpus_to_preempt: %*pb",
cpumask_pr_args(pcpu->cpus_to_preempt));
+ if (!cpumask_empty(pcpu->cpus_to_preempt_lazy))
+ scx_dump_line(&ns, " preempt_lazy : %*pb",
+ cpumask_pr_args(pcpu->cpus_to_preempt_lazy));
if (!cpumask_empty(pcpu->cpus_to_wait))
scx_dump_line(&ns, " cpus_to_wait : %*pb",
cpumask_pr_args(pcpu->cpus_to_wait));
@@ -7200,6 +7232,7 @@ struct scx_sched *scx_alloc_and_add_sched(struct scx_enable_cmd *cmd,
if (!zalloc_cpumask_var_node(&pcpu->cpus_to_kick, GFP_KERNEL, node) ||
!zalloc_cpumask_var_node(&pcpu->cpus_to_kick_if_idle, GFP_KERNEL, node) ||
!zalloc_cpumask_var_node(&pcpu->cpus_to_preempt, GFP_KERNEL, node) ||
+ !zalloc_cpumask_var_node(&pcpu->cpus_to_preempt_lazy, GFP_KERNEL, node) ||
!zalloc_cpumask_var_node(&pcpu->cpus_to_wait, GFP_KERNEL, node)) {
ret = -ENOMEM;
goto err_free_pcpu;
@@ -7335,6 +7368,7 @@ struct scx_sched *scx_alloc_and_add_sched(struct scx_enable_cmd *cmd,
free_cpumask_var(pcpu->cpus_to_kick);
free_cpumask_var(pcpu->cpus_to_kick_if_idle);
free_cpumask_var(pcpu->cpus_to_preempt);
+ free_cpumask_var(pcpu->cpus_to_preempt_lazy);
free_cpumask_var(pcpu->cpus_to_wait);
}
for_each_possible_cpu(cpu) {
@@ -7953,7 +7987,7 @@ static bool bpf_scx_is_valid_access(int off, int size,
return btf_ctx_access(off, size, type, prog, info);
}
-/* common to both forms: only scx.disallow is writable */
+/* common to both forms: only the fields below are writable */
static int bpf_scx_btf_struct_access_common(const struct bpf_reg_state *reg,
int off, int size)
{
@@ -7964,7 +7998,6 @@ static int bpf_scx_btf_struct_access_common(const struct bpf_reg_state *reg,
off >= offsetof(struct task_struct, scx.disallow) &&
off + size <= offsetofend(struct task_struct, scx.disallow))
return SCALAR_VALUE;
-
return -EACCES;
}
@@ -8462,10 +8495,20 @@ static bool kick_one_cpu(s32 cpu, struct scx_sched_pcpu *pcpu, struct rq *this_r
const struct sched_class *cur_class;
bool should_wait = false;
bool kickable;
+ bool preempt, preempt_lazy, wait, immediate;
unsigned long flags;
raw_spin_rq_lock_irqsave(rq, flags);
cur_class = rq->curr->sched_class;
+ preempt = cpumask_test_cpu(cpu, pcpu->cpus_to_preempt);
+ preempt_lazy = cpumask_test_cpu(cpu, pcpu->cpus_to_preempt_lazy);
+ wait = cpumask_test_cpu(cpu, pcpu->cpus_to_wait);
+ /*
+ * Immediate preemption, waiting and a plain kick take precedence over
+ * lazy preemption. The lazy request still clears the slice, so all
+ * accumulated requests are served.
+ */
+ immediate = preempt || wait || cpumask_test_cpu(cpu, pcpu->cpus_to_kick);
/*
* During CPU hotplug, a CPU may depend on kicking itself to make
@@ -8479,19 +8522,23 @@ static bool kick_one_cpu(s32 cpu, struct scx_sched_pcpu *pcpu, struct rq *this_r
!sched_class_above(cur_class, &ext_sched_class);
if (kickable && !scx_missing_caps(pcpu->sch, cpu, SCX_CAP_BASE)) {
- if (cpumask_test_cpu(cpu, pcpu->cpus_to_preempt)) {
+ if (preempt || preempt_lazy) {
if (cur_class == &ext_sched_class) {
u64 caps = scx_caps_for_preempt(pcpu->sch, rq, 0);
- if (unlikely(scx_missing_caps(pcpu->sch, cpu, caps)))
+ if (unlikely(scx_missing_caps(pcpu->sch, cpu, caps))) {
__scx_add_event(pcpu->sch, SCX_EV_SUB_PREEMPT_DENIED, 1);
- else if (unlikely(!scx_set_task_slice(rq->curr, 0)))
+ /* degrade to a plain, immediate kick */
+ immediate = true;
+ } else if (unlikely(!scx_set_task_slice(rq->curr, 0))) {
__scx_add_event(pcpu->sch, SCX_EV_SLICE_DENIED, 1);
+ }
}
cpumask_clear_cpu(cpu, pcpu->cpus_to_preempt);
+ cpumask_clear_cpu(cpu, pcpu->cpus_to_preempt_lazy);
}
- if (cpumask_test_cpu(cpu, pcpu->cpus_to_wait)) {
+ if (wait) {
if (cur_class == &ext_sched_class) {
cpumask_set_cpu(cpu, this_scx->cpus_to_sync);
ksyncs[cpu] = rq->scx.kick_sync;
@@ -8500,12 +8547,16 @@ static bool kick_one_cpu(s32 cpu, struct scx_sched_pcpu *pcpu, struct rq *this_r
cpumask_clear_cpu(cpu, pcpu->cpus_to_wait);
}
- resched_curr(rq);
+ if (immediate)
+ resched_curr(rq);
+ else
+ scx_resched_curr_lazy(rq);
} else {
/* a kickable cpu was skipped solely for the missing caps */
if (kickable)
__scx_add_event(pcpu->sch, SCX_EV_SUB_KICK_DENIED, 1);
cpumask_clear_cpu(cpu, pcpu->cpus_to_preempt);
+ cpumask_clear_cpu(cpu, pcpu->cpus_to_preempt_lazy);
cpumask_clear_cpu(cpu, pcpu->cpus_to_wait);
}
@@ -8566,6 +8617,14 @@ static void kick_cpus_irq_workfn(struct irq_work *irq_work)
cpumask_clear_cpu(cpu, pcpu->cpus_to_kick_if_idle);
}
+ /*
+ * kick_one_cpu() clears the lazy bit of every cpu it visited
+ * above; visit the remaining requests which contain lazy
+ * preemption, see scx_kick_cpu().
+ */
+ for_each_cpu(cpu, pcpu->cpus_to_preempt_lazy)
+ kick_one_cpu(cpu, pcpu, this_rq, ksyncs);
+
for_each_cpu(cpu, pcpu->cpus_to_kick_if_idle) {
kick_one_cpu_if_idle(cpu, pcpu, this_rq);
cpumask_clear_cpu(cpu, pcpu->cpus_to_kick_if_idle);
@@ -9531,6 +9590,31 @@ __bpf_kfunc bool scx_bpf_task_set_dsq_vtime(struct task_struct *p, u64 vtime,
return true;
}
+/**
+ * scx_bpf_task_set_slice_expiry - Set task's slice expiry policy
+ * @p: task of interest
+ * @lazy: whether slice expiry should request lazy rescheduling
+ * @aux: implicit BPF argument to access bpf_prog_aux hidden from BPF progs
+ *
+ * Choose whether depletion of @p's slice at the scheduler tick requests lazy
+ * or immediate rescheduling. @p must be on the calling scheduler.
+ *
+ * Return %true on success, %false if @p is not on the calling scheduler.
+ */
+__bpf_kfunc bool scx_bpf_task_set_slice_expiry(struct task_struct *p, bool lazy,
+ const struct bpf_prog_aux *aux)
+{
+ struct scx_sched *sch;
+
+ guard(rcu)();
+ sch = scx_prog_sched(aux);
+ if (unlikely(!sch || !scx_task_on_sched(sch, p)))
+ return false;
+
+ WRITE_ONCE(p->scx.slice_expires_lazy, lazy);
+ return true;
+}
+
void scx_kick_cpu(struct scx_sched *sch, s32 cpu, u64 flags)
{
struct scx_sched_pcpu *pcpu;
@@ -9539,6 +9623,16 @@ void scx_kick_cpu(struct scx_sched *sch, s32 cpu, u64 flags)
if (!scx_kf_allowed_ctx(sch))
return;
+ if (unlikely(flags & ~(SCX_KICK_IDLE | SCX_KICK_PREEMPT | SCX_KICK_WAIT |
+ SCX_KICK_PREEMPT_LAZY))) {
+ scx_error(sch, "invalid kick flags 0x%llx", flags);
+ return;
+ }
+ if (unlikely((flags & SCX_KICK_IDLE) &&
+ (flags & (SCX_KICK_PREEMPT | SCX_KICK_PREEMPT_LAZY | SCX_KICK_WAIT)))) {
+ scx_error(sch, "PREEMPT/WAIT cannot be used with SCX_KICK_IDLE");
+ return;
+ }
local_irq_save(irq_flags);
@@ -9564,9 +9658,6 @@ void scx_kick_cpu(struct scx_sched *sch, s32 cpu, u64 flags)
if (flags & SCX_KICK_IDLE) {
struct rq *target_rq = cpu_rq(cpu);
- if (unlikely(flags & (SCX_KICK_PREEMPT | SCX_KICK_WAIT)))
- scx_error(sch, "PREEMPT/WAIT cannot be used with SCX_KICK_IDLE");
-
if (raw_spin_rq_trylock(target_rq)) {
if (can_skip_idle_kick(target_rq)) {
scx_rq_lock_drop(target_rq);
@@ -9578,12 +9669,15 @@ void scx_kick_cpu(struct scx_sched *sch, s32 cpu, u64 flags)
}
cpumask_set_cpu(cpu, pcpu->cpus_to_kick_if_idle);
} else {
- cpumask_set_cpu(cpu, pcpu->cpus_to_kick);
-
+ /* Accumulate requests and resolve their precedence at delivery. */
if (flags & SCX_KICK_PREEMPT)
cpumask_set_cpu(cpu, pcpu->cpus_to_preempt);
+ if (flags & SCX_KICK_PREEMPT_LAZY)
+ cpumask_set_cpu(cpu, pcpu->cpus_to_preempt_lazy);
if (flags & SCX_KICK_WAIT)
cpumask_set_cpu(cpu, pcpu->cpus_to_wait);
+ if (!(flags & SCX_KICK_PREEMPT_LAZY))
+ cpumask_set_cpu(cpu, pcpu->cpus_to_kick);
}
if (list_empty(&pcpu->to_kick_node))
@@ -9623,8 +9717,9 @@ __bpf_kfunc void scx_bpf_kick_cpu(s32 cpu, u64 flags, const struct bpf_prog_aux
* cid-addressed equivalent of scx_bpf_kick_cpu(). An invalid @cid aborts the
* scheduler via scx_cid_to_cpu(). Caps are enforced on the delivery path: a
* kick is dropped if the caller lacks baseline access on @cid, and a
- * %SCX_KICK_PREEMPT degrades to a plain reschedule if the caller lacks
- * %SCX_CAP_PREEMPT for a task outside its subtree.
+ * %SCX_KICK_PREEMPT or %SCX_KICK_PREEMPT_LAZY request degrades to a plain
+ * reschedule if the caller lacks %SCX_CAP_PREEMPT for a task outside its
+ * subtree.
*/
__bpf_kfunc void scx_bpf_kick_cid(s32 cid, u64 flags, const struct bpf_prog_aux *aux)
{
@@ -10691,6 +10786,7 @@ __bpf_kfunc_end_defs();
BTF_KFUNCS_START(scx_kfunc_ids_any)
BTF_ID_FLAGS(func, scx_bpf_task_set_slice, KF_IMPLICIT_ARGS | KF_RCU);
BTF_ID_FLAGS(func, scx_bpf_task_set_dsq_vtime, KF_IMPLICIT_ARGS | KF_RCU);
+BTF_ID_FLAGS(func, scx_bpf_task_set_slice_expiry, KF_IMPLICIT_ARGS | KF_RCU);
BTF_ID_FLAGS(func, scx_bpf_kick_cpu, KF_IMPLICIT_ARGS)
BTF_ID_FLAGS(func, scx_bpf_kick_cid, KF_IMPLICIT_ARGS)
BTF_ID_FLAGS(func, scx_bpf_dsq_nr_queued, KF_IMPLICIT_ARGS)
diff --git a/kernel/sched/ext/internal.h b/kernel/sched/ext/internal.h
index e1eb3a0d456cb..d73b10d692d21 100644
--- a/kernel/sched/ext/internal.h
+++ b/kernel/sched/ext/internal.h
@@ -215,6 +215,19 @@ enum scx_ops_flags {
*/
SCX_OPS_TID_TO_TASK = 1LLU << 8,
+ /*
+ * If set, tasks default to requesting lazy rescheduling when their slice
+ * runs out at the tick, the way fair.c expires a slice from update_curr().
+ * The default is copied to p->scx.slice_expires_lazy immediately before
+ * ops.enable(), after which scx_bpf_task_set_slice_expiry() may override
+ * it per task.
+ * A task in user space still reschedules on the way back from the tick; a
+ * task in the kernel runs on to its next return to user space or to the
+ * next tick, which promotes the request. No effect on kernels without
+ * lazy preemption. Rescheduling while disabling stays immediate.
+ */
+ SCX_OPS_LAZY_SLICE_EXPIRY = 1LLU << 9,
+
SCX_OPS_ALL_FLAGS = SCX_OPS_KEEP_BUILTIN_IDLE |
SCX_OPS_ENQ_LAST |
SCX_OPS_ENQ_EXITING |
@@ -223,7 +236,8 @@ enum scx_ops_flags {
SCX_OPS_SWITCH_PARTIAL |
SCX_OPS_BUILTIN_IDLE_PER_NODE |
SCX_OPS_ALWAYS_ENQ_IMMED |
- SCX_OPS_TID_TO_TASK,
+ SCX_OPS_TID_TO_TASK |
+ SCX_OPS_LAZY_SLICE_EXPIRY,
/* high 8 bits are internal, don't include in SCX_OPS_ALL_FLAGS */
__SCX_OPS_INTERNAL_MASK = 0xffLLU << 56,
@@ -1327,6 +1341,7 @@ struct scx_sched_pcpu {
cpumask_var_t cpus_to_kick;
cpumask_var_t cpus_to_kick_if_idle;
cpumask_var_t cpus_to_preempt;
+ cpumask_var_t cpus_to_preempt_lazy;
cpumask_var_t cpus_to_wait;
struct list_head to_kick_node;
@@ -1407,15 +1422,16 @@ struct scx_sched_pnode {
* the allocation pattern.
*
* ENQ_IMMED insert an IMMED task onto the cid's local DSQ
- * - kick the cid's cpu (except SCX_KICK_PREEMPT)
+ * - kick the cid's cpu (except SCX_KICK_PREEMPT and
+ * SCX_KICK_PREEMPT_LAZY)
*
* ENQ insert any task onto the cid's local DSQ (implies ENQ_IMMED)
*
* PREEMPT preempt any task running on the cid regardless of the owning
* sched (implies ENQ). Preempting a task in the sched's own subtree
* doesn't require any cap.
- * - SCX_ENQ_PREEMPT inserts
- * - SCX_KICK_PREEMPT kicks
+ * - SCX_ENQ_PREEMPT and SCX_ENQ_PREEMPT_LAZY inserts
+ * - SCX_KICK_PREEMPT and SCX_KICK_PREEMPT_LAZY kicks
*
* PERF control the cid's cpu power/perf management state, currently the
* cpufreq target set through scx_bpf_cidperf_set(). Hardware
@@ -1685,6 +1701,15 @@ enum scx_enq_flags {
*/
SCX_ENQ_PREEMPT = 1LLU << 32,
+ /*
+ * Like %SCX_ENQ_PREEMPT, but request lazy rescheduling. The current
+ * task's slice is still cleared immediately so that the next scheduling
+ * boundary observes the new ordering. %SCX_ENQ_PREEMPT takes precedence
+ * if both are specified. Implies %SCX_ENQ_HEAD, which is all it means on
+ * a non-local DSQ, as with %SCX_ENQ_PREEMPT.
+ */
+ SCX_ENQ_PREEMPT_LAZY = 1LLU << 35,
+
/*
* Only allowed on local DSQs. Guarantees that the task either gets
* on the CPU immediately and stays on it, or gets reenqueued back
@@ -1811,6 +1836,12 @@ enum scx_kick_flags {
* is not on SCX.
*/
SCX_KICK_WAIT = 1LLU << 2,
+
+ /*
+ * Like %SCX_KICK_PREEMPT, but request lazy rescheduling. If combined
+ * with %SCX_KICK_PREEMPT or %SCX_KICK_WAIT, rescheduling is immediate.
+ */
+ SCX_KICK_PREEMPT_LAZY = 1LLU << 3,
};
enum scx_tg_flags {
diff --git a/kernel/sched/ext/sub.c b/kernel/sched/ext/sub.c
index 380a5653dc529..a88b87614b55e 100644
--- a/kernel/sched/ext/sub.c
+++ b/kernel/sched/ext/sub.c
@@ -686,9 +686,10 @@ void scx_rescue_init(struct rq *rq)
* rescue is enabled, or @rq's reject DSQ after recording the reenq reason on
* @p.
*
- * %SCX_ENQ_IMMED, %SCX_ENQ_PREEMPT and %SCX_ENQ_HEAD are cleared when diverting
- * to rescue or reject. %SCX_ENQ_PREEMPT is also cleared on a fallback
- * migration-disabled admission.
+ * %SCX_ENQ_IMMED, %SCX_ENQ_PREEMPT, %SCX_ENQ_PREEMPT_LAZY and %SCX_ENQ_HEAD
+ * are cleared when diverting to rescue or reject. %SCX_ENQ_PREEMPT and
+ * %SCX_ENQ_PREEMPT_LAZY are also cleared on a fallback migration-disabled
+ * admission.
*
* Bypass doesn't need special-casing as a bypassing sched's tasks are enqueued
* to and run by its nearest non-bypassing ancestor. If root is bypassing, it
@@ -709,7 +710,7 @@ struct scx_dispatch_q *scx_resolve_local_dsq(struct scx_sched *sch, struct rq *r
* On a remote activation the scheduling sched (@asch) differs from
* @p's owner (@sch). Check caps against the scheduling sched.
*/
- if (*enq_flags & SCX_ENQ_PREEMPT)
+ if (*enq_flags & (SCX_ENQ_PREEMPT | SCX_ENQ_PREEMPT_LAZY))
needed |= scx_caps_for_preempt(asch, rq, *enq_flags);
missing = scx_missing_caps(asch, cpu_of(rq), needed);
@@ -726,7 +727,7 @@ struct scx_dispatch_q *scx_resolve_local_dsq(struct scx_sched *sch, struct rq *r
if (unlikely(!scx_rq_online(rq) || is_migration_disabled(p) ||
p->migration_pending)) {
__scx_add_event(sch, SCX_EV_SUB_FORCED_ADMIT, 1);
- *enq_flags &= ~SCX_ENQ_PREEMPT;
+ *enq_flags &= ~(SCX_ENQ_PREEMPT | SCX_ENQ_PREEMPT_LAZY);
return &rq->scx.local_dsq;
}
@@ -735,8 +736,8 @@ struct scx_dispatch_q *scx_resolve_local_dsq(struct scx_sched *sch, struct rq *r
* or HEAD - a diversion has no priority and IMMED is not allowed on
* non-local DSQs. Strip the enq and task flags along with the slice.
*/
- *enq_flags &= ~(SCX_ENQ_IMMED | SCX_ENQ_PREEMPT | SCX_ENQ_HEAD |
- SCX_ENQ_APPLY_SLICE | SCX_ENQ_SLICE_DFL);
+ *enq_flags &= ~(SCX_ENQ_IMMED | SCX_ENQ_PREEMPT | SCX_ENQ_PREEMPT_LAZY |
+ SCX_ENQ_HEAD | SCX_ENQ_APPLY_SLICE | SCX_ENQ_SLICE_DFL);
p->scx.flags &= ~SCX_TASK_IMMED;
/* the enqueuer opted for rescue instead of rejection and reenqueue */
diff --git a/tools/sched_ext/include/scx/compat.bpf.h b/tools/sched_ext/include/scx/compat.bpf.h
index 6944221f96cc0..4a9bf1a4bb4a8 100644
--- a/tools/sched_ext/include/scx/compat.bpf.h
+++ b/tools/sched_ext/include/scx/compat.bpf.h
@@ -403,6 +403,19 @@ static inline void scx_bpf_task_set_dsq_vtime(struct task_struct *p, u64 vtime)
p->scx.dsq_vtime = vtime;
}
+/*
+ * v7.4: scx_bpf_task_set_slice_expiry() added to enforce sub-scheduler task
+ * ownership. Preserve until v7.7.
+ */
+bool scx_bpf_task_set_slice_expiry___new(struct task_struct *p, bool lazy) __ksym __weak;
+
+static inline bool scx_bpf_task_set_slice_expiry(struct task_struct *p, bool lazy)
+{
+ if (bpf_ksym_exists(scx_bpf_task_set_slice_expiry___new))
+ return scx_bpf_task_set_slice_expiry___new(p, lazy);
+ return false;
+}
+
/*
* v7.1: New scx_bpf_dsq_reenq() that allows re-enqueues on more DSQs. This
* will eventually deprecate scx_bpf_reenqueue_local().
diff --git a/tools/sched_ext/include/scx/enum_defs.autogen.h b/tools/sched_ext/include/scx/enum_defs.autogen.h
index 63b6b14b19bd4..f1554c22071ff 100644
--- a/tools/sched_ext/include/scx/enum_defs.autogen.h
+++ b/tools/sched_ext/include/scx/enum_defs.autogen.h
@@ -85,6 +85,7 @@
#define HAVE_SCX_ENQ_HEAD
#define HAVE_SCX_ENQ_CPU_SELECTED
#define HAVE_SCX_ENQ_PREEMPT
+#define HAVE_SCX_ENQ_PREEMPT_LAZY
#define HAVE_SCX_ENQ_IMMED
#define HAVE_SCX_ENQ_RESCUE
#define HAVE_SCX_ENQ_REENQ
@@ -148,6 +149,7 @@
#define HAVE_SCX_KF_ALLOW_SELECT_CPU
#define HAVE_SCX_KICK_IDLE
#define HAVE_SCX_KICK_PREEMPT
+#define HAVE_SCX_KICK_PREEMPT_LAZY
#define HAVE_SCX_KICK_WAIT
#define HAVE_SCX_OPI_BEGIN
#define HAVE_SCX_OPI_NORMAL_BEGIN
@@ -164,6 +166,7 @@
#define HAVE_SCX_OPS_BUILTIN_IDLE_PER_NODE
#define HAVE_SCX_OPS_ALWAYS_ENQ_IMMED
#define HAVE_SCX_OPS_TID_TO_TASK
+#define HAVE_SCX_OPS_LAZY_SLICE_EXPIRY
#define HAVE_SCX_OPS_ALL_FLAGS
#define HAVE___SCX_OPS_INTERNAL_MASK
#define HAVE_SCX_OPS_HAS_CPU_PREEMPT
diff --git a/tools/sched_ext/include/scx/enums.autogen.bpf.h b/tools/sched_ext/include/scx/enums.autogen.bpf.h
index 7268131010de3..2cec24beb2d80 100644
--- a/tools/sched_ext/include/scx/enums.autogen.bpf.h
+++ b/tools/sched_ext/include/scx/enums.autogen.bpf.h
@@ -109,6 +109,9 @@ const volatile u64 __SCX_KICK_IDLE __weak;
const volatile u64 __SCX_KICK_PREEMPT __weak;
#define SCX_KICK_PREEMPT __SCX_KICK_PREEMPT
+const volatile u64 __SCX_KICK_PREEMPT_LAZY __weak;
+#define SCX_KICK_PREEMPT_LAZY __SCX_KICK_PREEMPT_LAZY
+
const volatile u64 __SCX_KICK_WAIT __weak;
#define SCX_KICK_WAIT __SCX_KICK_WAIT
@@ -121,6 +124,9 @@ const volatile u64 __SCX_ENQ_HEAD __weak;
const volatile u64 __SCX_ENQ_PREEMPT __weak;
#define SCX_ENQ_PREEMPT __SCX_ENQ_PREEMPT
+const volatile u64 __SCX_ENQ_PREEMPT_LAZY __weak;
+#define SCX_ENQ_PREEMPT_LAZY __SCX_ENQ_PREEMPT_LAZY
+
const volatile u64 __SCX_ENQ_IMMED __weak;
#define SCX_ENQ_IMMED __SCX_ENQ_IMMED
diff --git a/tools/sched_ext/include/scx/enums.autogen.h b/tools/sched_ext/include/scx/enums.autogen.h
index e616326545172..dd762ee0ddb36 100644
--- a/tools/sched_ext/include/scx/enums.autogen.h
+++ b/tools/sched_ext/include/scx/enums.autogen.h
@@ -40,10 +40,12 @@
SCX_ENUM_SET(skel, scx_ent_dsq_flags, SCX_TASK_DSQ_ON_PRIQ); \
SCX_ENUM_SET(skel, scx_kick_flags, SCX_KICK_IDLE); \
SCX_ENUM_SET(skel, scx_kick_flags, SCX_KICK_PREEMPT); \
+ SCX_ENUM_SET(skel, scx_kick_flags, SCX_KICK_PREEMPT_LAZY); \
SCX_ENUM_SET(skel, scx_kick_flags, SCX_KICK_WAIT); \
SCX_ENUM_SET(skel, scx_enq_flags, SCX_ENQ_WAKEUP); \
SCX_ENUM_SET(skel, scx_enq_flags, SCX_ENQ_HEAD); \
SCX_ENUM_SET(skel, scx_enq_flags, SCX_ENQ_PREEMPT); \
+ SCX_ENUM_SET(skel, scx_enq_flags, SCX_ENQ_PREEMPT_LAZY); \
SCX_ENUM_SET(skel, scx_enq_flags, SCX_ENQ_IMMED); \
SCX_ENUM_SET(skel, scx_enq_flags, SCX_ENQ_RESCUE); \
SCX_ENUM_SET(skel, scx_enq_flags, SCX_ENQ_REENQ); \
diff --git a/tools/sched_ext/include/scx/enums_abi.autogen.h b/tools/sched_ext/include/scx/enums_abi.autogen.h
index d53899764f5ac..672c02a497d14 100644
--- a/tools/sched_ext/include/scx/enums_abi.autogen.h
+++ b/tools/sched_ext/include/scx/enums_abi.autogen.h
@@ -97,6 +97,7 @@ static const struct __scx_enum_abi_val __scx_enum_abi_vals[]
{ "scx_enq_flags", "SCX_ENQ_HEAD", 0x10000LLU },
{ "scx_enq_flags", "SCX_ENQ_CPU_SELECTED", 0x100000LLU },
{ "scx_enq_flags", "SCX_ENQ_PREEMPT", 0x100000000LLU },
+ { "scx_enq_flags", "SCX_ENQ_PREEMPT_LAZY", 0x800000000LLU },
{ "scx_enq_flags", "SCX_ENQ_IMMED", 0x200000000LLU },
{ "scx_enq_flags", "SCX_ENQ_RESCUE", 0x400000000LLU },
{ "scx_enq_flags", "SCX_ENQ_REENQ", 0x10000000000LLU },
@@ -160,6 +161,7 @@ static const struct __scx_enum_abi_val __scx_enum_abi_vals[]
{ "scx_kf_allow_flags", "SCX_KF_ALLOW_SELECT_CPU", 0x20LLU },
{ "scx_kick_flags", "SCX_KICK_IDLE", 0x1LLU },
{ "scx_kick_flags", "SCX_KICK_PREEMPT", 0x2LLU },
+ { "scx_kick_flags", "SCX_KICK_PREEMPT_LAZY", 0x8LLU },
{ "scx_kick_flags", "SCX_KICK_WAIT", 0x4LLU },
{ "scx_opi", "SCX_OPI_BEGIN", 0x0LLU },
{ "scx_opi", "SCX_OPI_NORMAL_BEGIN", 0x0LLU },
@@ -176,7 +178,8 @@ static const struct __scx_enum_abi_val __scx_enum_abi_vals[]
{ "scx_ops_flags", "SCX_OPS_BUILTIN_IDLE_PER_NODE", 0x40LLU },
{ "scx_ops_flags", "SCX_OPS_ALWAYS_ENQ_IMMED", 0x80LLU },
{ "scx_ops_flags", "SCX_OPS_TID_TO_TASK", 0x100LLU },
- { "scx_ops_flags", "SCX_OPS_ALL_FLAGS", 0x1ffLLU },
+ { "scx_ops_flags", "SCX_OPS_LAZY_SLICE_EXPIRY", 0x200LLU },
+ { "scx_ops_flags", "SCX_OPS_ALL_FLAGS", 0x3ffLLU },
{ "scx_ops_flags", "__SCX_OPS_INTERNAL_MASK", 0xff00000000000000LLU },
{ "scx_ops_flags", "SCX_OPS_HAS_CPU_PREEMPT", 0x100000000000000LLU },
{ "scx_ops_state", "SCX_OPSS_NONE", 0x0LLU },
--
2.55.0
^ permalink raw reply [flat|nested] 8+ messages in thread
* [PATCH 2/2] selftests/sched_ext: Add lazy preemption tests
2026-09-14 8:47 [PATCHSET v2 sched_ext/for-7.4] sched_ext: Add lazy preemption support Andrea Righi
2026-09-14 8:47 ` [PATCH 1/2] " Andrea Righi
@ 2026-09-14 8:47 ` Andrea Righi
2026-09-14 14:55 ` Cheng-Yang Chou
1 sibling, 1 reply; 8+ messages in thread
From: Andrea Righi @ 2026-09-14 8:47 UTC (permalink / raw)
To: Tejun Heo, David Vernet, Changwoo Min
Cc: Emil Tsalapatis, sched-ext, linux-kernel
Add trace-based coverage for immediate and lazy preemption. An fexit
probe on __resched_curr() records the requested TIF and the current task
slice, while the stopping callback verifies that the task reaches a
scheduling boundary.
Exercise kick requests individually, in both orders and combined in one
call. Verify that immediate preemption and WAIT take precedence over
lazy preemption, and that combining immediate and lazy enqueue
preemption follows the same rule. Also test overriding the expiry
default in both directions through scx_bpf_task_set_slice_expiry().
Extend the NO_HZ_FULL test with infinite-slice victims. Verify that lazy
enqueue and kick requests restart a stopped tick and make forward
progress. Keep invalid kick flag coverage and skip modes not exposed by
the running kernel.
Signed-off-by: Andrea Righi <arighi@nvidia.com>
---
tools/testing/selftests/sched_ext/Makefile | 1 +
tools/testing/selftests/sched_ext/kick.bpf.c | 166 ++++++
tools/testing/selftests/sched_ext/kick.c | 526 ++++++++++++++++++
.../selftests/sched_ext/nohz_tick.bpf.c | 54 +-
tools/testing/selftests/sched_ext/nohz_tick.c | 189 ++++++-
5 files changed, 929 insertions(+), 7 deletions(-)
create mode 100644 tools/testing/selftests/sched_ext/kick.bpf.c
create mode 100644 tools/testing/selftests/sched_ext/kick.c
diff --git a/tools/testing/selftests/sched_ext/Makefile b/tools/testing/selftests/sched_ext/Makefile
index 5f5dd9ab903ae..c4ec9b21a4c2a 100644
--- a/tools/testing/selftests/sched_ext/Makefile
+++ b/tools/testing/selftests/sched_ext/Makefile
@@ -172,6 +172,7 @@ auto-test-targets := \
exit \
hotplug \
init_enable_count \
+ kick \
maximal \
maybe_null \
minimal \
diff --git a/tools/testing/selftests/sched_ext/kick.bpf.c b/tools/testing/selftests/sched_ext/kick.bpf.c
new file mode 100644
index 0000000000000..03ddc44faf5c4
--- /dev/null
+++ b/tools/testing/selftests/sched_ext/kick.bpf.c
@@ -0,0 +1,166 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (c) 2026 NVIDIA CORPORATION & AFFILIATES
+ */
+#include <scx/common.bpf.h>
+
+char _license[] SEC("license") = "GPL";
+
+enum kick_scenario {
+ KICK_IMMEDIATE,
+ KICK_LAZY,
+ KICK_LAZY_THEN_IMMEDIATE,
+ KICK_IMMEDIATE_THEN_LAZY,
+ KICK_PLAIN_THEN_LAZY,
+ KICK_LAZY_THEN_PLAIN,
+ KICK_BOTH,
+ KICK_LAZY_WAIT,
+ ENQ_BOTH,
+ TICK_EXPIRY,
+ INVALID_KICK_IDLE,
+ INVALID_KICK_UNKNOWN,
+};
+
+enum kick_state {
+ KICK_STATE_IDLE,
+ KICK_STATE_ARMED,
+ KICK_STATE_QUEUED,
+ KICK_STATE_RESCHED,
+ KICK_STATE_DONE,
+};
+
+const volatile u32 scenario;
+const volatile s32 victim_pid;
+const volatile s32 target_cpu;
+const volatile s32 slice_expiry_override = -1;
+
+u32 state;
+u64 slice_before;
+u64 slice_at_resched;
+s32 resched_tif;
+
+UEI_DEFINE(uei);
+
+static bool is_trace_scenario(void)
+{
+ return scenario <= TICK_EXPIRY;
+}
+
+void BPF_STRUCT_OPS(kick_enqueue, struct task_struct *p, u64 enq_flags)
+{
+ switch (scenario) {
+ case ENQ_BOTH:
+ if (p->pid == victim_pid) {
+ scx_bpf_dsq_insert(p, SCX_DSQ_GLOBAL, SCX_SLICE_INF,
+ enq_flags);
+ } else if (state == KICK_STATE_QUEUED) {
+ scx_bpf_dsq_insert(p, SCX_DSQ_LOCAL, SCX_SLICE_DFL,
+ enq_flags | SCX_ENQ_PREEMPT |
+ SCX_ENQ_PREEMPT_LAZY);
+ } else {
+ scx_bpf_dsq_insert(p, SCX_DSQ_GLOBAL, SCX_SLICE_DFL,
+ enq_flags);
+ }
+ return;
+ case INVALID_KICK_IDLE:
+ scx_bpf_kick_cpu(scx_bpf_task_cpu(p), SCX_KICK_PREEMPT_LAZY | SCX_KICK_IDLE);
+ break;
+ case INVALID_KICK_UNKNOWN:
+ scx_bpf_kick_cpu(scx_bpf_task_cpu(p), 1LLU << 63);
+ break;
+ }
+
+ scx_bpf_dsq_insert(p, SCX_DSQ_GLOBAL, SCX_SLICE_DFL, enq_flags);
+}
+
+static void set_slice_expiry_override(struct task_struct *p)
+{
+ if (p->pid == victim_pid && slice_expiry_override >= 0)
+ scx_bpf_task_set_slice_expiry(p, slice_expiry_override);
+}
+
+void BPF_STRUCT_OPS(kick_running, struct task_struct *p)
+{
+ if (!is_trace_scenario() || p->pid != victim_pid)
+ return;
+ set_slice_expiry_override(p);
+ if (__sync_val_compare_and_swap(&state, KICK_STATE_ARMED, KICK_STATE_QUEUED) !=
+ KICK_STATE_ARMED)
+ return;
+
+ slice_before = p->scx.slice;
+
+ switch (scenario) {
+ case KICK_IMMEDIATE:
+ scx_bpf_kick_cpu(target_cpu, SCX_KICK_PREEMPT);
+ break;
+ case KICK_LAZY:
+ scx_bpf_kick_cpu(target_cpu, SCX_KICK_PREEMPT_LAZY);
+ break;
+ case KICK_LAZY_THEN_IMMEDIATE:
+ scx_bpf_kick_cpu(target_cpu, SCX_KICK_PREEMPT_LAZY);
+ scx_bpf_kick_cpu(target_cpu, SCX_KICK_PREEMPT);
+ break;
+ case KICK_IMMEDIATE_THEN_LAZY:
+ scx_bpf_kick_cpu(target_cpu, SCX_KICK_PREEMPT);
+ scx_bpf_kick_cpu(target_cpu, SCX_KICK_PREEMPT_LAZY);
+ break;
+ case KICK_PLAIN_THEN_LAZY:
+ scx_bpf_kick_cpu(target_cpu, 0);
+ scx_bpf_kick_cpu(target_cpu, SCX_KICK_PREEMPT_LAZY);
+ break;
+ case KICK_LAZY_THEN_PLAIN:
+ scx_bpf_kick_cpu(target_cpu, SCX_KICK_PREEMPT_LAZY);
+ scx_bpf_kick_cpu(target_cpu, 0);
+ break;
+ case KICK_BOTH:
+ scx_bpf_kick_cpu(target_cpu, SCX_KICK_PREEMPT |
+ SCX_KICK_PREEMPT_LAZY);
+ break;
+ case KICK_LAZY_WAIT:
+ scx_bpf_kick_cpu(target_cpu, SCX_KICK_PREEMPT_LAZY |
+ SCX_KICK_WAIT);
+ break;
+ case ENQ_BOTH:
+ /* The userspace controller wakes a competing task. */
+ break;
+ case TICK_EXPIRY:
+ /* no kick: the slice runs out at the tick */
+ break;
+ }
+}
+
+SEC("fexit/__resched_curr")
+int BPF_PROG(kick_need_resched, struct rq *rq, int tif)
+{
+ struct task_struct *task = BPF_CORE_READ(rq, curr);
+
+ if (!task || BPF_CORE_READ(task, pid) != victim_pid ||
+ BPF_CORE_READ(rq, cpu) != target_cpu || state != KICK_STATE_QUEUED)
+ return 0;
+
+ slice_at_resched = BPF_CORE_READ(task, scx.slice);
+ resched_tif = tif;
+ state = KICK_STATE_RESCHED;
+ return 0;
+}
+
+void BPF_STRUCT_OPS(kick_stopping, struct task_struct *p, bool runnable)
+{
+ if (p->pid == victim_pid && state == KICK_STATE_RESCHED)
+ state = KICK_STATE_DONE;
+}
+
+void BPF_STRUCT_OPS(kick_exit, struct scx_exit_info *ei)
+{
+ UEI_RECORD(uei, ei);
+}
+
+SEC(".struct_ops.link")
+struct sched_ext_ops kick_ops = {
+ .enqueue = (void *)kick_enqueue,
+ .running = (void *)kick_running,
+ .stopping = (void *)kick_stopping,
+ .exit = (void *)kick_exit,
+ .name = "kick",
+};
diff --git a/tools/testing/selftests/sched_ext/kick.c b/tools/testing/selftests/sched_ext/kick.c
new file mode 100644
index 0000000000000..3fa112a1de607
--- /dev/null
+++ b/tools/testing/selftests/sched_ext/kick.c
@@ -0,0 +1,526 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (c) 2026 NVIDIA CORPORATION & AFFILIATES
+ */
+#define _GNU_SOURCE
+#include <bpf/bpf.h>
+#include <linux/sched.h>
+#include <sched.h>
+#include <signal.h>
+#include <stdio.h>
+#include <string.h>
+#include <sys/wait.h>
+#include <unistd.h>
+#include <scx/common.h>
+
+#include "kick.bpf.skel.h"
+#include "scx_test.h"
+
+#define WAIT_LOOPS 3000
+
+enum kick_scenario {
+ KICK_IMMEDIATE,
+ KICK_LAZY,
+ KICK_LAZY_THEN_IMMEDIATE,
+ KICK_IMMEDIATE_THEN_LAZY,
+ KICK_PLAIN_THEN_LAZY,
+ KICK_LAZY_THEN_PLAIN,
+ KICK_BOTH,
+ KICK_LAZY_WAIT,
+ ENQ_BOTH,
+ TICK_EXPIRY,
+ INVALID_KICK_IDLE,
+ INVALID_KICK_UNKNOWN,
+};
+
+enum kick_state {
+ KICK_STATE_IDLE,
+ KICK_STATE_ARMED,
+ KICK_STATE_QUEUED,
+ KICK_STATE_RESCHED,
+ KICK_STATE_DONE,
+};
+
+struct victim {
+ pid_t pid;
+ int start_fd;
+};
+
+struct observation {
+ u64 slice_before;
+ u64 slice_at_resched;
+ s32 resched_tif;
+};
+
+static bool enum_supported(const char *type, const char *name)
+{
+ u64 value;
+
+ return __COMPAT_read_enum(type, name, &value);
+}
+
+static int pick_target_cpu(void)
+{
+ cpu_set_t mask;
+ int cpu;
+
+ if (sched_getaffinity(0, sizeof(mask), &mask))
+ return -1;
+
+ for (cpu = 0; cpu < CPU_SETSIZE; cpu++)
+ if (CPU_ISSET(cpu, &mask))
+ return cpu;
+
+ return -1;
+}
+
+static struct victim spawn_victim(int cpu)
+{
+ struct victim victim = { .pid = -1, .start_fd = -1 };
+ int ready[2], start[2];
+ char byte = 1;
+
+ if (pipe(ready))
+ return victim;
+ if (pipe(start)) {
+ close(ready[0]);
+ close(ready[1]);
+ return victim;
+ }
+
+ victim.pid = fork();
+ if (!victim.pid) {
+ cpu_set_t mask;
+
+ close(ready[0]);
+ close(start[1]);
+ CPU_ZERO(&mask);
+ CPU_SET(cpu, &mask);
+ if (sched_setaffinity(0, sizeof(mask), &mask))
+ _exit(1);
+ if (write(ready[1], &byte, 1) != 1)
+ _exit(1);
+ close(ready[1]);
+ if (read(start[0], &byte, 1) != 1)
+ _exit(1);
+ close(start[0]);
+ for (;;)
+ asm volatile("" ::: "memory");
+ }
+ if (victim.pid < 0) {
+ close(ready[0]);
+ close(ready[1]);
+ close(start[0]);
+ close(start[1]);
+ return victim;
+ }
+
+ close(ready[1]);
+ close(start[0]);
+ if (read(ready[0], &byte, 1) != 1) {
+ close(ready[0]);
+ close(start[1]);
+ kill(victim.pid, SIGKILL);
+ waitpid(victim.pid, NULL, 0);
+ victim.pid = -1;
+ return victim;
+ }
+ close(ready[0]);
+ victim.start_fd = start[1];
+ return victim;
+}
+
+static void stop_victim(struct victim *victim)
+{
+ if (victim->start_fd >= 0)
+ close(victim->start_fd);
+ if (victim->pid > 0) {
+ kill(victim->pid, SIGKILL);
+ waitpid(victim->pid, NULL, 0);
+ }
+}
+
+static bool start_victim(struct victim *victim)
+{
+ char byte = 1;
+
+ if (write(victim->start_fd, &byte, 1) != 1)
+ return false;
+ close(victim->start_fd);
+ victim->start_fd = -1;
+ return true;
+}
+
+static bool wait_for_state(struct kick *skel, u32 wanted)
+{
+ int i;
+
+ for (i = 0; i < WAIT_LOOPS; i++) {
+ if (__atomic_load_n(&skel->bss->state, __ATOMIC_ACQUIRE) == wanted)
+ return true;
+ if (skel->data->uei.kind != EXIT_KIND(SCX_EXIT_NONE))
+ return false;
+ usleep(1000);
+ }
+ return false;
+}
+
+static enum scx_test_status trace_one(u32 scenario, u64 ops_flags,
+ s32 slice_expiry_override,
+ struct observation *obs)
+{
+ struct bpf_link *ops_link = NULL;
+ struct kick *skel = NULL;
+ struct victim challenger = { .pid = -1, .start_fd = -1 };
+ struct victim victim;
+ enum scx_test_status ret = SCX_TEST_FAIL;
+ int cpu = pick_target_cpu();
+
+ if (cpu < 0) {
+ SCX_ERR("No available CPU");
+ return SCX_TEST_FAIL;
+ }
+ victim = spawn_victim(cpu);
+ if (victim.pid < 0) {
+ SCX_ERR("Failed to spawn victim");
+ return SCX_TEST_FAIL;
+ }
+ if (scenario == ENQ_BOTH) {
+ challenger = spawn_victim(cpu);
+ if (challenger.pid < 0) {
+ SCX_ERR("Failed to spawn enqueue challenger");
+ goto out;
+ }
+ }
+
+ skel = kick__open();
+ if (!skel) {
+ SCX_ERR("Failed to open scenario %u", scenario);
+ goto out;
+ }
+ SCX_ENUM_INIT(skel);
+ skel->rodata->scenario = scenario;
+ skel->rodata->victim_pid = victim.pid;
+ skel->rodata->target_cpu = cpu;
+ skel->rodata->slice_expiry_override = slice_expiry_override;
+ skel->struct_ops.kick_ops->flags |= ops_flags;
+ if (kick__load(skel)) {
+ SCX_ERR("Failed to load scenario %u", scenario);
+ goto out;
+ }
+
+ bpf_map__set_autoattach(skel->maps.kick_ops, false);
+ if (kick__attach(skel)) {
+ SCX_ERR("Failed to attach __resched_curr tracer");
+ goto out;
+ }
+ skel->bss->state = KICK_STATE_ARMED;
+ ops_link = bpf_map__attach_struct_ops(skel->maps.kick_ops);
+ if (!ops_link) {
+ SCX_ERR("Failed to attach scenario %u", scenario);
+ goto out;
+ }
+ if (!start_victim(&victim)) {
+ SCX_ERR("Failed to start victim");
+ goto out;
+ }
+ if (scenario == ENQ_BOTH) {
+ if (!wait_for_state(skel, KICK_STATE_QUEUED)) {
+ SCX_ERR("Enqueue scenario did not arm");
+ goto out;
+ }
+ if (!start_victim(&challenger)) {
+ SCX_ERR("Failed to start enqueue challenger");
+ goto out;
+ }
+ }
+ if (!wait_for_state(skel, KICK_STATE_DONE)) {
+ SCX_ERR("Scenario %u stopped in state %u, exit kind %d", scenario, skel->bss->state,
+ skel->data->uei.kind);
+ goto out;
+ }
+
+ obs->slice_before = skel->bss->slice_before;
+ obs->slice_at_resched = skel->bss->slice_at_resched;
+ obs->resched_tif = skel->bss->resched_tif;
+ ret = SCX_TEST_PASS;
+out:
+ stop_victim(&challenger);
+ stop_victim(&victim);
+ if (ops_link)
+ bpf_link__destroy(ops_link);
+ if (skel)
+ kick__destroy(skel);
+ return ret;
+}
+
+static bool observation_valid(const struct observation *obs)
+{
+ return obs->slice_before > 0 && !obs->slice_at_resched;
+}
+
+static int active_lazy_mode(void)
+{
+ char buf[128];
+ FILE *file;
+
+ file = fopen("/sys/kernel/debug/sched/preempt", "r");
+ if (!file)
+ return -1;
+ if (!fgets(buf, sizeof(buf), file)) {
+ fclose(file);
+ return -1;
+ }
+ fclose(file);
+
+ if (strstr(buf, "(lazy)"))
+ return 1;
+ if (strstr(buf, "(full)"))
+ return 0;
+ return -1;
+}
+
+static enum scx_test_status setup_immediate(void **ctx)
+{
+ if (!enum_supported("scx_kick_flags", "SCX_KICK_PREEMPT")) {
+ printf("SKIP: SCX_KICK_PREEMPT is not supported\n");
+ return SCX_TEST_SKIP;
+ }
+ return SCX_TEST_PASS;
+}
+
+static enum scx_test_status setup_lazy(void **ctx)
+{
+ if (!enum_supported("scx_kick_flags", "SCX_KICK_PREEMPT_LAZY")) {
+ printf("SKIP: SCX_KICK_PREEMPT_LAZY is not supported\n");
+ return SCX_TEST_SKIP;
+ }
+ return setup_immediate(ctx);
+}
+
+static enum scx_test_status setup_tick(void **ctx)
+{
+ if (!enum_supported("scx_ops_flags", "SCX_OPS_LAZY_SLICE_EXPIRY")) {
+ printf("SKIP: SCX_OPS_LAZY_SLICE_EXPIRY is not supported\n");
+ return SCX_TEST_SKIP;
+ }
+ return setup_lazy(ctx);
+}
+
+static enum scx_test_status setup_coalesce(void **ctx)
+{
+ if (!enum_supported("scx_enq_flags", "SCX_ENQ_PREEMPT_LAZY")) {
+ printf("SKIP: SCX_ENQ_PREEMPT_LAZY is not supported\n");
+ return SCX_TEST_SKIP;
+ }
+ return setup_lazy(ctx);
+}
+
+static enum scx_test_status setup_invalid(void **ctx)
+{
+ return setup_lazy(ctx);
+}
+
+static enum scx_test_status run_immediate(void *ctx)
+{
+ struct observation obs;
+
+ SCX_EQ(trace_one(KICK_IMMEDIATE, 0, -1, &obs), SCX_TEST_PASS);
+ SCX_ASSERT(observation_valid(&obs));
+ return SCX_TEST_PASS;
+}
+
+static enum scx_test_status run_lazy(void *ctx)
+{
+ struct observation immediate, lazy;
+ int lazy_mode;
+
+ SCX_EQ(trace_one(KICK_IMMEDIATE, 0, -1, &immediate), SCX_TEST_PASS);
+ SCX_EQ(trace_one(KICK_LAZY, 0, -1, &lazy), SCX_TEST_PASS);
+ SCX_ASSERT(observation_valid(&immediate));
+ SCX_ASSERT(observation_valid(&lazy));
+
+ lazy_mode = active_lazy_mode();
+ if (lazy_mode > 0)
+ SCX_FAIL_IF(lazy.resched_tif == immediate.resched_tif,
+ "Lazy mode used immediate TIF %d", lazy.resched_tif);
+ else if (!lazy_mode)
+ SCX_EQ(lazy.resched_tif, immediate.resched_tif);
+ else
+ printf("INFO: preemption mode unavailable; lazy TIF was %d, immediate TIF was %d\n",
+ lazy.resched_tif, immediate.resched_tif);
+
+ return SCX_TEST_PASS;
+}
+
+static enum scx_test_status run_coalesce(void *ctx)
+{
+ struct observation immediate, lazy_first, immediate_first;
+ struct observation plain_first, lazy_then_plain;
+ struct observation both, lazy_wait, enq_both;
+
+ SCX_EQ(trace_one(KICK_IMMEDIATE, 0, -1, &immediate), SCX_TEST_PASS);
+ SCX_EQ(trace_one(KICK_LAZY_THEN_IMMEDIATE, 0, -1, &lazy_first), SCX_TEST_PASS);
+ SCX_EQ(trace_one(KICK_IMMEDIATE_THEN_LAZY, 0, -1, &immediate_first), SCX_TEST_PASS);
+ SCX_ASSERT(observation_valid(&lazy_first));
+ SCX_ASSERT(observation_valid(&immediate_first));
+ SCX_EQ(lazy_first.resched_tif, immediate.resched_tif);
+ SCX_EQ(immediate_first.resched_tif, immediate.resched_tif);
+
+ /*
+ * A plain kick in the same batch doesn't clear the slice by itself.
+ * The lazy preemption must still expire it, and the plain kick must
+ * still reschedule immediately, whichever came first.
+ */
+ SCX_EQ(trace_one(KICK_PLAIN_THEN_LAZY, 0, -1, &plain_first), SCX_TEST_PASS);
+ SCX_EQ(trace_one(KICK_LAZY_THEN_PLAIN, 0, -1, &lazy_then_plain), SCX_TEST_PASS);
+ SCX_ASSERT(observation_valid(&plain_first));
+ SCX_ASSERT(observation_valid(&lazy_then_plain));
+ SCX_EQ(plain_first.resched_tif, immediate.resched_tif);
+ SCX_EQ(lazy_then_plain.resched_tif, immediate.resched_tif);
+
+ /* Immediate kick and WAIT both take precedence over lazy preemption. */
+ SCX_EQ(trace_one(KICK_BOTH, 0, -1, &both), SCX_TEST_PASS);
+ SCX_EQ(trace_one(KICK_LAZY_WAIT, 0, -1, &lazy_wait), SCX_TEST_PASS);
+ SCX_ASSERT(observation_valid(&both));
+ SCX_ASSERT(observation_valid(&lazy_wait));
+ SCX_EQ(both.resched_tif, immediate.resched_tif);
+ SCX_EQ(lazy_wait.resched_tif, immediate.resched_tif);
+
+ /* Immediate enqueue preemption likewise takes precedence over lazy. */
+ SCX_EQ(trace_one(ENQ_BOTH, 0, -1, &enq_both), SCX_TEST_PASS);
+ SCX_ASSERT(observation_valid(&enq_both));
+ SCX_EQ(enq_both.resched_tif, immediate.resched_tif);
+ return SCX_TEST_PASS;
+}
+
+/*
+ * A slice running out at the tick reschedules immediately by default and
+ * lazily with SCX_OPS_LAZY_SLICE_EXPIRY, the way fair.c expires a slice.
+ */
+static enum scx_test_status run_tick(void *ctx)
+{
+ struct observation immediate, lazy, force_lazy, force_immediate;
+ u64 lazy_flag;
+ int lazy_mode;
+
+ SCX_ASSERT(__COMPAT_read_enum("scx_ops_flags", "SCX_OPS_LAZY_SLICE_EXPIRY", &lazy_flag));
+ SCX_EQ(trace_one(TICK_EXPIRY, 0, -1, &immediate), SCX_TEST_PASS);
+ SCX_EQ(trace_one(TICK_EXPIRY, lazy_flag, -1, &lazy), SCX_TEST_PASS);
+ SCX_EQ(trace_one(TICK_EXPIRY, 0, 1, &force_lazy), SCX_TEST_PASS);
+ SCX_EQ(trace_one(TICK_EXPIRY, lazy_flag, 0, &force_immediate), SCX_TEST_PASS);
+ SCX_ASSERT(observation_valid(&immediate));
+ SCX_ASSERT(observation_valid(&lazy));
+ SCX_ASSERT(observation_valid(&force_lazy));
+ SCX_ASSERT(observation_valid(&force_immediate));
+
+ lazy_mode = active_lazy_mode();
+ if (lazy_mode > 0)
+ SCX_FAIL_IF(lazy.resched_tif == immediate.resched_tif,
+ "Lazy slice expiry used immediate TIF %d", lazy.resched_tif);
+ else if (!lazy_mode)
+ SCX_EQ(lazy.resched_tif, immediate.resched_tif);
+ else
+ printf("INFO: preemption mode unavailable; lazy TIF was %d, immediate TIF was %d\n",
+ lazy.resched_tif, immediate.resched_tif);
+ SCX_EQ(force_lazy.resched_tif, lazy.resched_tif);
+ SCX_EQ(force_immediate.resched_tif, immediate.resched_tif);
+
+ return SCX_TEST_PASS;
+}
+
+static enum scx_test_status invalid_one(u32 scenario)
+{
+ struct bpf_link *ops_link = NULL;
+ struct kick *skel = NULL;
+ struct victim victim;
+ enum scx_test_status ret = SCX_TEST_FAIL;
+ int cpu = pick_target_cpu();
+ int i;
+
+ if (cpu < 0)
+ return SCX_TEST_FAIL;
+ victim = spawn_victim(cpu);
+ if (victim.pid < 0)
+ return SCX_TEST_FAIL;
+
+ skel = kick__open();
+ if (!skel)
+ goto out;
+ SCX_ENUM_INIT(skel);
+ skel->rodata->scenario = scenario;
+ if (kick__load(skel))
+ goto out;
+ ops_link = bpf_map__attach_struct_ops(skel->maps.kick_ops);
+ if (!ops_link || !start_victim(&victim))
+ goto out;
+
+ for (i = 0; i < WAIT_LOOPS; i++) {
+ if (skel->data->uei.kind == EXIT_KIND(SCX_EXIT_ERROR)) {
+ ret = SCX_TEST_PASS;
+ break;
+ }
+ usleep(1000);
+ }
+out:
+ stop_victim(&victim);
+ if (ops_link)
+ bpf_link__destroy(ops_link);
+ if (skel)
+ kick__destroy(skel);
+ return ret;
+}
+
+static enum scx_test_status run_invalid(void *ctx)
+{
+ u32 scenario;
+
+ for (scenario = INVALID_KICK_IDLE; scenario <= INVALID_KICK_UNKNOWN; scenario++)
+ SCX_EQ(invalid_one(scenario), SCX_TEST_PASS);
+ return SCX_TEST_PASS;
+}
+
+static struct scx_test kick_immediate = {
+ .name = "kick_immediate",
+ .description = "Trace immediate kick slice expiration and rescheduling",
+ .setup = setup_immediate,
+ .run = run_immediate,
+};
+
+static struct scx_test kick_lazy = {
+ .name = "kick_lazy",
+ .description = "Trace lazy kick slice expiration and rescheduling",
+ .setup = setup_lazy,
+ .run = run_lazy,
+};
+
+static struct scx_test kick_coalesce = {
+ .name = "kick_coalesce",
+ .description = "Verify lazy preemption coalesces with immediate requests",
+ .setup = setup_coalesce,
+ .run = run_coalesce,
+};
+
+static struct scx_test kick_tick = {
+ .name = "kick_tick",
+ .description = "Trace slice expiry at the tick, immediate and lazy",
+ .setup = setup_tick,
+ .run = run_tick,
+};
+
+static struct scx_test kick_invalid = {
+ .name = "kick_invalid",
+ .description = "Verify invalid kick flag combinations fail",
+ .setup = setup_invalid,
+ .run = run_invalid,
+};
+
+__attribute__((constructor))
+static void register_kick_tests(void)
+{
+ scx_test_register(&kick_immediate);
+ scx_test_register(&kick_lazy);
+ scx_test_register(&kick_coalesce);
+ scx_test_register(&kick_tick);
+ scx_test_register(&kick_invalid);
+}
diff --git a/tools/testing/selftests/sched_ext/nohz_tick.bpf.c b/tools/testing/selftests/sched_ext/nohz_tick.bpf.c
index 6998c5dd6bcb9..fc89079d19e79 100644
--- a/tools/testing/selftests/sched_ext/nohz_tick.bpf.c
+++ b/tools/testing/selftests/sched_ext/nohz_tick.bpf.c
@@ -9,10 +9,23 @@
char _license[] SEC("license") = "GPL";
const volatile s32 test_cpu;
-bool finite_phase;
+enum nohz_phase {
+ NOHZ_PHASE_INF,
+ NOHZ_PHASE_FINITE,
+ NOHZ_PHASE_LAZY_ENQ,
+ NOHZ_PHASE_LAZY_KICK,
+};
+
+u32 phase;
+s32 victim_pid;
+s32 challenger_pid;
+s32 trigger_pid;
u64 nr_inf_running;
u64 nr_finite_running;
u64 nr_finite_ticks;
+u64 nr_lazy_victim_running;
+u64 nr_lazy_enq_running;
+u64 nr_lazy_kick_running;
UEI_DEFINE(uei);
@@ -24,9 +37,31 @@ s32 BPF_STRUCT_OPS(nohz_tick_select_cpu, struct task_struct *p, s32 prev_cpu,
void BPF_STRUCT_OPS(nohz_tick_enqueue, struct task_struct *p, u64 enq_flags)
{
- u64 slice = finite_phase ? 1000000ULL : SCX_SLICE_INF;
+ u64 slice;
+ u64 dsq_id = SCX_DSQ_GLOBAL;
+
+ switch (phase) {
+ case NOHZ_PHASE_INF:
+ slice = SCX_SLICE_INF;
+ break;
+ case NOHZ_PHASE_FINITE:
+ slice = 1000000ULL;
+ break;
+ case NOHZ_PHASE_LAZY_ENQ:
+ case NOHZ_PHASE_LAZY_KICK:
+ dsq_id = SCX_DSQ_LOCAL;
+ slice = p->pid == victim_pid ? SCX_SLICE_INF : SCX_SLICE_DFL;
+ if (phase == NOHZ_PHASE_LAZY_ENQ && p->pid == challenger_pid)
+ enq_flags |= SCX_ENQ_PREEMPT_LAZY;
+ break;
+ default:
+ slice = SCX_SLICE_DFL;
+ break;
+ }
- scx_bpf_dsq_insert(p, SCX_DSQ_GLOBAL, slice, enq_flags);
+ scx_bpf_dsq_insert(p, dsq_id, slice, enq_flags);
+ if (phase == NOHZ_PHASE_LAZY_KICK && p->pid == trigger_pid)
+ scx_bpf_kick_cpu(test_cpu, SCX_KICK_PREEMPT_LAZY);
if (enq_flags & SCX_ENQ_LAST)
scx_bpf_kick_cpu(test_cpu, SCX_KICK_IDLE);
}
@@ -36,15 +71,22 @@ void BPF_STRUCT_OPS(nohz_tick_running, struct task_struct *p)
if (bpf_get_smp_processor_id() != test_cpu)
return;
- if (finite_phase)
+ if (phase == NOHZ_PHASE_FINITE)
__sync_fetch_and_add(&nr_finite_running, 1);
- else
+ else if (phase == NOHZ_PHASE_INF)
__sync_fetch_and_add(&nr_inf_running, 1);
+ else if (p->pid == victim_pid)
+ __sync_fetch_and_add(&nr_lazy_victim_running, 1);
+ else if (phase == NOHZ_PHASE_LAZY_ENQ && p->pid == challenger_pid)
+ __sync_fetch_and_add(&nr_lazy_enq_running, 1);
+ else if (phase == NOHZ_PHASE_LAZY_KICK && p->pid == challenger_pid)
+ __sync_fetch_and_add(&nr_lazy_kick_running, 1);
}
void BPF_STRUCT_OPS(nohz_tick_tick, struct task_struct *p)
{
- if (bpf_get_smp_processor_id() == test_cpu && finite_phase)
+ if (bpf_get_smp_processor_id() == test_cpu &&
+ phase == NOHZ_PHASE_FINITE)
__sync_fetch_and_add(&nr_finite_ticks, 1);
}
diff --git a/tools/testing/selftests/sched_ext/nohz_tick.c b/tools/testing/selftests/sched_ext/nohz_tick.c
index 028f54391c2ca..a5266a5412935 100644
--- a/tools/testing/selftests/sched_ext/nohz_tick.c
+++ b/tools/testing/selftests/sched_ext/nohz_tick.c
@@ -34,6 +34,20 @@ struct nohz_tick_ctx {
struct nohz_tick *skel;
cpu_set_t original_mask;
int test_cpu;
+ int housekeeping_cpu;
+ bool lazy_supported;
+};
+
+enum nohz_phase {
+ NOHZ_PHASE_INF,
+ NOHZ_PHASE_FINITE,
+ NOHZ_PHASE_LAZY_ENQ,
+ NOHZ_PHASE_LAZY_KICK,
+};
+
+struct gated_worker {
+ pid_t pid;
+ int start_fd;
};
static int first_allowed_cpu(const cpu_set_t *mask, int first, int last)
@@ -132,6 +146,87 @@ static void stop_worker(pid_t pid)
waitpid(pid, NULL, 0);
}
+static struct gated_worker spawn_gated_worker(int cpu)
+{
+ struct gated_worker worker = { .pid = -1, .start_fd = -1 };
+ int ready[2], start[2];
+ pid_t parent = getpid();
+ char byte = 1;
+
+ if (pipe(ready))
+ return worker;
+ if (pipe(start)) {
+ close(ready[0]);
+ close(ready[1]);
+ return worker;
+ }
+
+ worker.pid = fork();
+ if (!worker.pid) {
+ struct sched_param param = {};
+ cpu_set_t mask;
+
+ close(ready[0]);
+ close(start[1]);
+ if (prctl(PR_SET_PDEATHSIG, SIGKILL) || getppid() != parent)
+ _exit(1);
+ CPU_ZERO(&mask);
+ CPU_SET(cpu, &mask);
+ if (sched_setaffinity(0, sizeof(mask), &mask))
+ _exit(1);
+ if (sched_setscheduler(0, SCHED_EXT, ¶m))
+ _exit(1);
+ if (write(ready[1], &byte, 1) != 1)
+ _exit(1);
+ close(ready[1]);
+ if (read(start[0], &byte, 1) != 1)
+ _exit(1);
+ close(start[0]);
+ for (;;)
+ asm volatile("" ::: "memory");
+ }
+ if (worker.pid < 0) {
+ close(ready[0]);
+ close(ready[1]);
+ close(start[0]);
+ close(start[1]);
+ return worker;
+ }
+
+ close(ready[1]);
+ close(start[0]);
+ if (read(ready[0], &byte, 1) != 1) {
+ close(ready[0]);
+ close(start[1]);
+ kill(worker.pid, SIGKILL);
+ waitpid(worker.pid, NULL, 0);
+ worker.pid = -1;
+ return worker;
+ }
+ close(ready[0]);
+ worker.start_fd = start[1];
+ return worker;
+}
+
+static bool start_gated_worker(struct gated_worker *worker)
+{
+ char byte = 1;
+
+ if (write(worker->start_fd, &byte, 1) != 1)
+ return false;
+ close(worker->start_fd);
+ worker->start_fd = -1;
+ return true;
+}
+
+static void stop_gated_worker(struct gated_worker *worker)
+{
+ if (worker->start_fd >= 0)
+ close(worker->start_fd);
+ stop_worker(worker->pid);
+ worker->pid = -1;
+}
+
static int pause_worker(pid_t pid)
{
int status;
@@ -163,6 +258,7 @@ static enum scx_test_status setup(void **ctx_ptr)
{
struct nohz_tick_ctx *ctx;
cpu_set_t controller_mask;
+ u64 enum_value;
int cpu;
ctx = calloc(1, sizeof(*ctx));
@@ -189,6 +285,13 @@ static enum scx_test_status setup(void **ctx_ptr)
}
ctx->test_cpu = cpu;
+ ctx->housekeeping_cpu = first_allowed_cpu(&controller_mask, 0,
+ CPU_SETSIZE - 1);
+ ctx->lazy_supported =
+ __COMPAT_read_enum("scx_enq_flags", "SCX_ENQ_PREEMPT_LAZY",
+ &enum_value) &&
+ __COMPAT_read_enum("scx_kick_flags", "SCX_KICK_PREEMPT_LAZY",
+ &enum_value);
ctx->skel = nohz_tick__open();
if (!ctx->skel) {
free(ctx);
@@ -220,6 +323,9 @@ static enum scx_test_status run(void *ctx_ptr)
struct nohz_tick_ctx *ctx = ctx_ptr;
struct nohz_tick *skel = ctx->skel;
struct bpf_link *link = NULL;
+ struct gated_worker victim = { .pid = -1, .start_fd = -1 };
+ struct gated_worker challenger = { .pid = -1, .start_fd = -1 };
+ struct gated_worker trigger = { .pid = -1, .start_fd = -1 };
enum scx_test_status status = SCX_TEST_FAIL;
pid_t finite_worker = -1;
pid_t inf_worker = -1;
@@ -260,7 +366,8 @@ static enum scx_test_status run(void *ctx_ptr)
/*
* The next EXT task receives a finite slice and must restart the tick.
*/
- __atomic_store_n(&skel->bss->finite_phase, true, __ATOMIC_RELEASE);
+ __atomic_store_n(&skel->bss->phase, NOHZ_PHASE_FINITE,
+ __ATOMIC_RELEASE);
finite_worker = start_worker(ctx->test_cpu);
if (finite_worker < 0) {
SCX_ERR("Failed to start finite-slice worker (%d)", errno);
@@ -308,7 +415,84 @@ static enum scx_test_status run(void *ctx_ptr)
finite_ticks));
goto out;
}
+ stop_worker(finite_worker);
+ finite_worker = -1;
+ stop_worker(inf_worker);
+ inf_worker = -1;
+ if (!ctx->lazy_supported)
+ goto check_exit;
+
+ /*
+ * A lazy local enqueue must restart the tick after clearing the slice of
+ * an infinite-slice task on a full-dynticks CPU.
+ */
+ __atomic_store_n(&skel->bss->phase, NOHZ_PHASE_LAZY_ENQ,
+ __ATOMIC_RELEASE);
+ victim = spawn_gated_worker(ctx->test_cpu);
+ challenger = spawn_gated_worker(ctx->test_cpu);
+ if (victim.pid < 0 || challenger.pid < 0) {
+ SCX_ERR("Failed to spawn lazy-enqueue workers");
+ goto out;
+ }
+ skel->bss->victim_pid = victim.pid;
+ skel->bss->challenger_pid = challenger.pid;
+ if (!start_gated_worker(&victim) ||
+ !wait_for_counter(&skel->bss->nr_lazy_victim_running, 1,
+ PHASE_TIMEOUT_MS)) {
+ SCX_ERR("Lazy-enqueue victim was not scheduled");
+ goto out;
+ }
+ usleep(100000);
+
+ if (!start_gated_worker(&challenger) ||
+ !wait_for_counter(&skel->bss->nr_lazy_enq_running, 1,
+ PHASE_TIMEOUT_MS)) {
+ SCX_ERR("Lazy enqueue made no progress on CPU %d", ctx->test_cpu);
+ goto out;
+ }
+ stop_gated_worker(&challenger);
+ stop_gated_worker(&victim);
+
+ /* Repeat with a lazy kick delivered from a housekeeping CPU. */
+ __atomic_store_n(&skel->bss->phase, NOHZ_PHASE_LAZY_KICK,
+ __ATOMIC_RELEASE);
+ victim = spawn_gated_worker(ctx->test_cpu);
+ challenger = spawn_gated_worker(ctx->test_cpu);
+ trigger = spawn_gated_worker(ctx->housekeeping_cpu);
+ if (victim.pid < 0 || challenger.pid < 0 || trigger.pid < 0) {
+ SCX_ERR("Failed to spawn lazy-kick workers");
+ goto out;
+ }
+ skel->bss->victim_pid = victim.pid;
+ skel->bss->challenger_pid = challenger.pid;
+ skel->bss->trigger_pid = trigger.pid;
+ if (!start_gated_worker(&victim) ||
+ !wait_for_counter(&skel->bss->nr_lazy_victim_running, 2,
+ PHASE_TIMEOUT_MS)) {
+ SCX_ERR("Lazy-kick victim was not scheduled");
+ goto out;
+ }
+ if (!start_gated_worker(&challenger)) {
+ SCX_ERR("Failed to start lazy-kick challenger");
+ goto out;
+ }
+ usleep(100000);
+ if (__atomic_load_n(&skel->bss->nr_lazy_kick_running,
+ __ATOMIC_RELAXED)) {
+ SCX_ERR("Lazy-kick challenger ran before the kick");
+ goto out;
+ }
+ if (!start_gated_worker(&trigger) ||
+ !wait_for_counter(&skel->bss->nr_lazy_kick_running, 1,
+ PHASE_TIMEOUT_MS)) {
+ SCX_ERR("Lazy kick made no progress on CPU %d", ctx->test_cpu);
+ goto out;
+ }
+ stop_gated_worker(&trigger);
+ stop_gated_worker(&challenger);
+ stop_gated_worker(&victim);
+check_exit:
if (skel->data->uei.kind != EXIT_KIND(SCX_EXIT_NONE)) {
SCX_ERR("Scheduler exited unexpectedly (kind=%llu code=%lld)",
(unsigned long long)skel->data->uei.kind,
@@ -321,6 +505,9 @@ static enum scx_test_status run(void *ctx_ptr)
(unsigned long long)skel->bss->nr_finite_ticks);
status = SCX_TEST_PASS;
out:
+ stop_gated_worker(&trigger);
+ stop_gated_worker(&challenger);
+ stop_gated_worker(&victim);
stop_worker(finite_worker);
stop_worker(inf_worker);
if (link)
--
2.55.0
^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: [PATCH 2/2] selftests/sched_ext: Add lazy preemption tests
2026-09-14 8:47 ` [PATCH 2/2] selftests/sched_ext: Add lazy preemption tests Andrea Righi
@ 2026-09-14 14:55 ` Cheng-Yang Chou
2026-09-15 13:35 ` Andrea Righi
0 siblings, 1 reply; 8+ messages in thread
From: Cheng-Yang Chou @ 2026-09-14 14:55 UTC (permalink / raw)
To: Andrea Righi
Cc: Tejun Heo, David Vernet, Changwoo Min, Emil Tsalapatis,
sched-ext, linux-kernel, Ching-Chun Huang, Chia-Ping Tsai,
chengyang.chou
Hi Andrea,
On Mon, Sep 14, 2026 at 10:47:46AM +0200, Andrea Righi wrote:
> Add trace-based coverage for immediate and lazy preemption. An fexit
> probe on __resched_curr() records the requested TIF and the current task
> slice, while the stopping callback verifies that the task reaches a
> scheduling boundary.
>
> Exercise kick requests individually, in both orders and combined in one
> call. Verify that immediate preemption and WAIT take precedence over
> lazy preemption, and that combining immediate and lazy enqueue
> preemption follows the same rule. Also test overriding the expiry
> default in both directions through scx_bpf_task_set_slice_expiry().
>
> Extend the NO_HZ_FULL test with infinite-slice victims. Verify that lazy
> enqueue and kick requests restart a stopped tick and make forward
> progress. Keep invalid kick flag coverage and skip modes not exposed by
> the running kernel.
>
> Signed-off-by: Andrea Righi <arighi@nvidia.com>
[...]
Didn't have time to go through the whole series, but I applied it on
for-next and built with PREEMPT_LAZY=y and PREEMPT_DYNAMIC=n:
INFO: preemption mode unavailable; lazy TIF was 5, immediate TIF was 4
ok 2 kick_lazy #
INFO: preemption mode unavailable; lazy TIF was 5, immediate TIF was 4
ok 4 kick_tick #
PASSED: 6
> +static int active_lazy_mode(void)
> +{
> + char buf[128];
> + FILE *file;
> +
> + file = fopen("/sys/kernel/debug/sched/preempt", "r");
> + if (!file)
> + return -1;
sched_init_debug() only creates that file under CONFIG_PREEMPT_DYNAMIC,
and PREEMPT_LAZY can be built without it ("select PREEMPT_BUILD if
!PREEMPT_DYNAMIC"), so the two tests pass without comparing the TIFs.
Would something like this work?
if (!file) {
#if defined(CONFIG_PREEMPT_LAZY) && !defined(CONFIG_PREEMPT_DYNAMIC)
return 1;
#else
return -1;
#endif
}
Thanks.
> + if (!fgets(buf, sizeof(buf), file)) {
> + fclose(file);
> + return -1;
> + }
> + fclose(file);
> +
> + if (strstr(buf, "(lazy)"))
> + return 1;
> + if (strstr(buf, "(full)"))
> + return 0;
> + return -1;
> +}
> +
--
Cheers,
Cheng-Yang
^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: [PATCH 2/2] selftests/sched_ext: Add lazy preemption tests
2026-09-14 14:55 ` Cheng-Yang Chou
@ 2026-09-15 13:35 ` Andrea Righi
0 siblings, 0 replies; 8+ messages in thread
From: Andrea Righi @ 2026-09-15 13:35 UTC (permalink / raw)
To: Cheng-Yang Chou
Cc: Tejun Heo, David Vernet, Changwoo Min, Emil Tsalapatis,
sched-ext, linux-kernel, Ching-Chun Huang, Chia-Ping Tsai,
chengyang.chou
On Mon, Sep 14, 2026 at 10:55:56PM +0800, Cheng-Yang Chou wrote:
> Hi Andrea,
>
> On Mon, Sep 14, 2026 at 10:47:46AM +0200, Andrea Righi wrote:
> > Add trace-based coverage for immediate and lazy preemption. An fexit
> > probe on __resched_curr() records the requested TIF and the current task
> > slice, while the stopping callback verifies that the task reaches a
> > scheduling boundary.
> >
> > Exercise kick requests individually, in both orders and combined in one
> > call. Verify that immediate preemption and WAIT take precedence over
> > lazy preemption, and that combining immediate and lazy enqueue
> > preemption follows the same rule. Also test overriding the expiry
> > default in both directions through scx_bpf_task_set_slice_expiry().
> >
> > Extend the NO_HZ_FULL test with infinite-slice victims. Verify that lazy
> > enqueue and kick requests restart a stopped tick and make forward
> > progress. Keep invalid kick flag coverage and skip modes not exposed by
> > the running kernel.
> >
> > Signed-off-by: Andrea Righi <arighi@nvidia.com>
>
> [...]
>
> Didn't have time to go through the whole series, but I applied it on
> for-next and built with PREEMPT_LAZY=y and PREEMPT_DYNAMIC=n:
>
> INFO: preemption mode unavailable; lazy TIF was 5, immediate TIF was 4
> ok 2 kick_lazy #
> INFO: preemption mode unavailable; lazy TIF was 5, immediate TIF was 4
> ok 4 kick_tick #
> PASSED: 6
>
> > +static int active_lazy_mode(void)
> > +{
> > + char buf[128];
> > + FILE *file;
> > +
> > + file = fopen("/sys/kernel/debug/sched/preempt", "r");
> > + if (!file)
> > + return -1;
>
> sched_init_debug() only creates that file under CONFIG_PREEMPT_DYNAMIC,
> and PREEMPT_LAZY can be built without it ("select PREEMPT_BUILD if
> !PREEMPT_DYNAMIC"), so the two tests pass without comparing the TIFs.
>
> Would something like this work?
>
> if (!file) {
> #if defined(CONFIG_PREEMPT_LAZY) && !defined(CONFIG_PREEMPT_DYNAMIC)
> return 1;
> #else
> return -1;
> #endif
Ah yes, makes sense, we can include autoconf.h and check that.
I'll include this fix in the next version.
Thanks,
-Andrea
> }
>
> Thanks.
>
> > + if (!fgets(buf, sizeof(buf), file)) {
> > + fclose(file);
> > + return -1;
> > + }
> > + fclose(file);
> > +
> > + if (strstr(buf, "(lazy)"))
> > + return 1;
> > + if (strstr(buf, "(full)"))
> > + return 0;
> > + return -1;
> > +}
> > +
>
> --
> Cheers,
> Cheng-Yang
^ permalink raw reply [flat|nested] 8+ messages in thread
* [PATCH 2/2] selftests/sched_ext: Add lazy preemption tests
2026-09-15 19:45 [PATCHSET v5 sched_ext/for-7.4] sched_ext: Add lazy preemption support Andrea Righi
@ 2026-09-15 19:45 ` Andrea Righi
0 siblings, 0 replies; 8+ messages in thread
From: Andrea Righi @ 2026-09-15 19:45 UTC (permalink / raw)
To: Tejun Heo, David Vernet, Changwoo Min
Cc: Emil Tsalapatis, Cheng-Yang Chou, sched-ext, linux-kernel
Add trace-based coverage for immediate and lazy preemption. An fexit
probe on __resched_curr() records the requested TIF and the current task
slice, while the stopping callback verifies that the task reaches a
scheduling boundary.
Exercise kick requests individually, in both orders and combined in one
call. Verify that immediate preemption and WAIT take precedence over
lazy preemption, and that combining immediate and lazy enqueue
preemption follows the same rule. Also test overriding the expiry
default in both directions through scx_bpf_task_set_slice_expiry().
Extend the NO_HZ_FULL test with infinite-slice victims. Verify that lazy
enqueue and kick requests restart a stopped tick and make forward
progress. Keep invalid kick flag coverage and skip modes not exposed by
the running kernel.
Cc: Cheng-Yang Chou <yphbchou0911@gmail.com>
Signed-off-by: Andrea Righi <arighi@nvidia.com>
---
tools/testing/selftests/sched_ext/Makefile | 1 +
tools/testing/selftests/sched_ext/kick.bpf.c | 182 ++++++
tools/testing/selftests/sched_ext/kick.c | 617 ++++++++++++++++++
.../selftests/sched_ext/nohz_tick.bpf.c | 56 +-
tools/testing/selftests/sched_ext/nohz_tick.c | 249 ++++++-
5 files changed, 1078 insertions(+), 27 deletions(-)
create mode 100644 tools/testing/selftests/sched_ext/kick.bpf.c
create mode 100644 tools/testing/selftests/sched_ext/kick.c
diff --git a/tools/testing/selftests/sched_ext/Makefile b/tools/testing/selftests/sched_ext/Makefile
index 5f5dd9ab903ae..c4ec9b21a4c2a 100644
--- a/tools/testing/selftests/sched_ext/Makefile
+++ b/tools/testing/selftests/sched_ext/Makefile
@@ -172,6 +172,7 @@ auto-test-targets := \
exit \
hotplug \
init_enable_count \
+ kick \
maximal \
maybe_null \
minimal \
diff --git a/tools/testing/selftests/sched_ext/kick.bpf.c b/tools/testing/selftests/sched_ext/kick.bpf.c
new file mode 100644
index 0000000000000..5a64e19246004
--- /dev/null
+++ b/tools/testing/selftests/sched_ext/kick.bpf.c
@@ -0,0 +1,182 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (c) 2026 NVIDIA CORPORATION & AFFILIATES
+ */
+#include <scx/common.bpf.h>
+
+char _license[] SEC("license") = "GPL";
+
+enum kick_scenario {
+ KICK_IMMEDIATE,
+ KICK_LAZY,
+ KICK_LAZY_THEN_IMMEDIATE,
+ KICK_IMMEDIATE_THEN_LAZY,
+ KICK_PLAIN_THEN_LAZY,
+ KICK_LAZY_THEN_PLAIN,
+ KICK_BOTH,
+ KICK_LAZY_WAIT,
+ ENQ_BOTH,
+ TICK_EXPIRY,
+ INVALID_KICK_IDLE,
+ INVALID_KICK_UNKNOWN,
+};
+
+enum kick_state {
+ KICK_STATE_IDLE,
+ KICK_STATE_ARMED,
+ KICK_STATE_QUEUED,
+ KICK_STATE_RESCHED,
+ KICK_STATE_DONE,
+};
+
+const volatile u32 scenario;
+const volatile s32 victim_pid;
+const volatile s32 challenger_pid;
+const volatile s32 target_cpu;
+const volatile s32 slice_expiry_override = -1;
+
+u32 state;
+u64 slice_before;
+u64 slice_at_resched;
+s32 resched_tif;
+u64 nr_wait_callbacks;
+bool enq_preempt_issued;
+
+UEI_DEFINE(uei);
+
+static bool is_trace_scenario(void)
+{
+ return scenario <= TICK_EXPIRY;
+}
+
+void BPF_STRUCT_OPS(kick_enqueue, struct task_struct *p, u64 enq_flags)
+{
+ switch (scenario) {
+ case ENQ_BOTH:
+ if (p->pid == victim_pid) {
+ scx_bpf_dsq_insert(p, SCX_DSQ_GLOBAL, SCX_SLICE_INF,
+ enq_flags);
+ } else if (p->pid == challenger_pid &&
+ state == KICK_STATE_QUEUED) {
+ enq_preempt_issued = true;
+ scx_bpf_dsq_insert(p, SCX_DSQ_LOCAL, SCX_SLICE_DFL,
+ enq_flags | SCX_ENQ_PREEMPT |
+ SCX_ENQ_PREEMPT_LAZY);
+ } else {
+ scx_bpf_dsq_insert(p, SCX_DSQ_GLOBAL, SCX_SLICE_DFL,
+ enq_flags);
+ }
+ return;
+ case INVALID_KICK_IDLE:
+ scx_bpf_kick_cpu(scx_bpf_task_cpu(p), SCX_KICK_PREEMPT_LAZY | SCX_KICK_IDLE);
+ break;
+ case INVALID_KICK_UNKNOWN:
+ scx_bpf_kick_cpu(scx_bpf_task_cpu(p), 1LLU << 63);
+ break;
+ }
+
+ scx_bpf_dsq_insert(p, SCX_DSQ_GLOBAL, SCX_SLICE_DFL, enq_flags);
+}
+
+static void set_slice_expiry_override(struct task_struct *p)
+{
+ if (p->pid == victim_pid && slice_expiry_override >= 0)
+ scx_bpf_task_set_slice_expiry(p, slice_expiry_override);
+}
+
+void BPF_STRUCT_OPS(kick_running, struct task_struct *p)
+{
+ if (!is_trace_scenario() || p->pid != victim_pid)
+ return;
+ set_slice_expiry_override(p);
+ if (__sync_val_compare_and_swap(&state, KICK_STATE_ARMED, KICK_STATE_QUEUED) !=
+ KICK_STATE_ARMED)
+ return;
+
+ slice_before = p->scx.slice;
+
+ switch (scenario) {
+ case KICK_IMMEDIATE:
+ scx_bpf_kick_cpu(target_cpu, SCX_KICK_PREEMPT);
+ break;
+ case KICK_LAZY:
+ scx_bpf_kick_cpu(target_cpu, SCX_KICK_PREEMPT_LAZY);
+ break;
+ case KICK_LAZY_THEN_IMMEDIATE:
+ scx_bpf_kick_cpu(target_cpu, SCX_KICK_PREEMPT_LAZY);
+ scx_bpf_kick_cpu(target_cpu, SCX_KICK_PREEMPT);
+ break;
+ case KICK_IMMEDIATE_THEN_LAZY:
+ scx_bpf_kick_cpu(target_cpu, SCX_KICK_PREEMPT);
+ scx_bpf_kick_cpu(target_cpu, SCX_KICK_PREEMPT_LAZY);
+ break;
+ case KICK_PLAIN_THEN_LAZY:
+ scx_bpf_kick_cpu(target_cpu, 0);
+ scx_bpf_kick_cpu(target_cpu, SCX_KICK_PREEMPT_LAZY);
+ break;
+ case KICK_LAZY_THEN_PLAIN:
+ scx_bpf_kick_cpu(target_cpu, SCX_KICK_PREEMPT_LAZY);
+ scx_bpf_kick_cpu(target_cpu, 0);
+ break;
+ case KICK_BOTH:
+ scx_bpf_kick_cpu(target_cpu, SCX_KICK_PREEMPT |
+ SCX_KICK_PREEMPT_LAZY);
+ break;
+ case KICK_LAZY_WAIT:
+ scx_bpf_kick_cpu(target_cpu, SCX_KICK_PREEMPT_LAZY |
+ SCX_KICK_WAIT);
+ break;
+ case ENQ_BOTH:
+ /* The userspace controller wakes a competing task. */
+ break;
+ case TICK_EXPIRY:
+ /* no kick: the slice runs out at the tick */
+ break;
+ }
+}
+
+SEC("fexit/__resched_curr")
+int BPF_PROG(kick_need_resched, struct rq *rq, int tif)
+{
+ struct task_struct *task = BPF_CORE_READ(rq, curr);
+
+ if (!task || BPF_CORE_READ(task, pid) != victim_pid ||
+ BPF_CORE_READ(rq, cpu) != target_cpu || state != KICK_STATE_QUEUED)
+ return 0;
+ if (scenario == ENQ_BOTH && !enq_preempt_issued)
+ return 0;
+
+ slice_at_resched = BPF_CORE_READ(task, scx.slice);
+ resched_tif = tif;
+ state = KICK_STATE_RESCHED;
+ return 0;
+}
+
+SEC("fentry/kick_sync_wait_bal_cb")
+int BPF_PROG(kick_wait_callback, struct rq *rq)
+{
+ if (scenario == KICK_LAZY_WAIT &&
+ BPF_CORE_READ(rq, cpu) == target_cpu)
+ __sync_fetch_and_add(&nr_wait_callbacks, 1);
+ return 0;
+}
+
+void BPF_STRUCT_OPS(kick_stopping, struct task_struct *p, bool runnable)
+{
+ if (p->pid == victim_pid && state == KICK_STATE_RESCHED)
+ state = KICK_STATE_DONE;
+}
+
+void BPF_STRUCT_OPS(kick_exit, struct scx_exit_info *ei)
+{
+ UEI_RECORD(uei, ei);
+}
+
+SEC(".struct_ops.link")
+struct sched_ext_ops kick_ops = {
+ .enqueue = (void *)kick_enqueue,
+ .running = (void *)kick_running,
+ .stopping = (void *)kick_stopping,
+ .exit = (void *)kick_exit,
+ .name = "kick",
+};
diff --git a/tools/testing/selftests/sched_ext/kick.c b/tools/testing/selftests/sched_ext/kick.c
new file mode 100644
index 0000000000000..118cc374e6b82
--- /dev/null
+++ b/tools/testing/selftests/sched_ext/kick.c
@@ -0,0 +1,617 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (c) 2026 NVIDIA CORPORATION & AFFILIATES
+ */
+#define _GNU_SOURCE
+#include <bpf/bpf.h>
+#include <errno.h>
+#include <linux/sched.h>
+#include <sched.h>
+#include <signal.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/prctl.h>
+#include <sys/wait.h>
+#include <unistd.h>
+#include <scx/common.h>
+
+#ifdef HAVE_GENHDR
+#include "autoconf.h"
+#endif
+
+#include "kick.bpf.skel.h"
+#include "scx_test.h"
+
+#define WAIT_LOOPS 3000
+
+enum kick_scenario {
+ KICK_IMMEDIATE,
+ KICK_LAZY,
+ KICK_LAZY_THEN_IMMEDIATE,
+ KICK_IMMEDIATE_THEN_LAZY,
+ KICK_PLAIN_THEN_LAZY,
+ KICK_LAZY_THEN_PLAIN,
+ KICK_BOTH,
+ KICK_LAZY_WAIT,
+ ENQ_BOTH,
+ TICK_EXPIRY,
+ INVALID_KICK_IDLE,
+ INVALID_KICK_UNKNOWN,
+};
+
+enum kick_state {
+ KICK_STATE_IDLE,
+ KICK_STATE_ARMED,
+ KICK_STATE_QUEUED,
+ KICK_STATE_RESCHED,
+ KICK_STATE_DONE,
+};
+
+struct victim {
+ pid_t pid;
+ int start_fd;
+};
+
+struct observation {
+ u64 slice_before;
+ u64 slice_at_resched;
+ u64 nr_wait_callbacks;
+ s32 resched_tif;
+};
+
+struct kick_ctx {
+ cpu_set_t original_mask;
+ int target_cpu;
+};
+
+static bool enum_supported(const char *type, const char *name)
+{
+ u64 value;
+
+ return __COMPAT_read_enum(type, name, &value);
+}
+
+static enum scx_test_status setup_controller(void **ctx_ptr)
+{
+ struct kick_ctx *ctx;
+ cpu_set_t controller_mask;
+ int cpu, controller_cpu = -1;
+
+ ctx = calloc(1, sizeof(*ctx));
+ SCX_FAIL_IF(!ctx, "Failed to allocate context");
+ if (sched_getaffinity(0, sizeof(ctx->original_mask),
+ &ctx->original_mask)) {
+ free(ctx);
+ SCX_FAIL("Failed to get affinity (%d)", errno);
+ }
+
+ for (cpu = 0; cpu < CPU_SETSIZE; cpu++) {
+ if (!CPU_ISSET(cpu, &ctx->original_mask))
+ continue;
+ if (controller_cpu < 0) {
+ controller_cpu = cpu;
+ } else {
+ ctx->target_cpu = cpu;
+ break;
+ }
+ }
+ if (cpu == CPU_SETSIZE) {
+ printf("SKIP: two allowed CPUs are required\n");
+ free(ctx);
+ return SCX_TEST_SKIP;
+ }
+
+ CPU_ZERO(&controller_mask);
+ CPU_SET(controller_cpu, &controller_mask);
+ if (sched_setaffinity(0, sizeof(controller_mask), &controller_mask)) {
+ free(ctx);
+ SCX_FAIL("Failed to pin controller to CPU %d (%d)",
+ controller_cpu, errno);
+ }
+
+ *ctx_ptr = ctx;
+ return SCX_TEST_PASS;
+}
+
+static void cleanup_controller(void *ctx_ptr)
+{
+ struct kick_ctx *ctx = ctx_ptr;
+
+ sched_setaffinity(0, sizeof(ctx->original_mask), &ctx->original_mask);
+ free(ctx);
+}
+
+static struct victim spawn_victim(int cpu)
+{
+ struct victim victim = { .pid = -1, .start_fd = -1 };
+ int ready[2], start[2];
+ pid_t parent = getpid();
+ char byte = 1;
+
+ if (pipe(ready))
+ return victim;
+ if (pipe(start)) {
+ close(ready[0]);
+ close(ready[1]);
+ return victim;
+ }
+
+ victim.pid = fork();
+ if (!victim.pid) {
+ cpu_set_t mask;
+
+ close(ready[0]);
+ close(start[1]);
+ if (prctl(PR_SET_PDEATHSIG, SIGKILL) || getppid() != parent)
+ _exit(1);
+ CPU_ZERO(&mask);
+ CPU_SET(cpu, &mask);
+ if (sched_setaffinity(0, sizeof(mask), &mask))
+ _exit(1);
+ if (write(ready[1], &byte, 1) != 1)
+ _exit(1);
+ close(ready[1]);
+ if (read(start[0], &byte, 1) != 1)
+ _exit(1);
+ close(start[0]);
+ for (;;)
+ asm volatile("" ::: "memory");
+ }
+ if (victim.pid < 0) {
+ close(ready[0]);
+ close(ready[1]);
+ close(start[0]);
+ close(start[1]);
+ return victim;
+ }
+
+ close(ready[1]);
+ close(start[0]);
+ if (read(ready[0], &byte, 1) != 1) {
+ close(ready[0]);
+ close(start[1]);
+ kill(victim.pid, SIGKILL);
+ waitpid(victim.pid, NULL, 0);
+ victim.pid = -1;
+ return victim;
+ }
+ close(ready[0]);
+ victim.start_fd = start[1];
+ return victim;
+}
+
+static void stop_victim(struct victim *victim)
+{
+ if (victim->start_fd >= 0)
+ close(victim->start_fd);
+ if (victim->pid > 0) {
+ kill(victim->pid, SIGKILL);
+ waitpid(victim->pid, NULL, 0);
+ }
+}
+
+static bool start_victim(struct victim *victim)
+{
+ char byte = 1;
+
+ if (write(victim->start_fd, &byte, 1) != 1)
+ return false;
+ close(victim->start_fd);
+ victim->start_fd = -1;
+ return true;
+}
+
+static bool wait_for_state(struct kick *skel, u32 wanted)
+{
+ int i;
+
+ for (i = 0; i < WAIT_LOOPS; i++) {
+ if (__atomic_load_n(&skel->bss->state, __ATOMIC_ACQUIRE) == wanted)
+ return true;
+ if (skel->data->uei.kind != EXIT_KIND(SCX_EXIT_NONE))
+ return false;
+ usleep(1000);
+ }
+ return false;
+}
+
+static enum scx_test_status trace_one(struct kick_ctx *ctx, u32 scenario,
+ u64 ops_flags,
+ s32 slice_expiry_override,
+ struct observation *obs)
+{
+ struct bpf_link *ops_link = NULL;
+ struct kick *skel = NULL;
+ struct victim challenger = { .pid = -1, .start_fd = -1 };
+ struct victim victim;
+ enum scx_test_status ret = SCX_TEST_FAIL;
+ int cpu = ctx->target_cpu;
+
+ victim = spawn_victim(cpu);
+ if (victim.pid < 0) {
+ SCX_ERR("Failed to spawn victim");
+ return SCX_TEST_FAIL;
+ }
+ if (scenario == ENQ_BOTH) {
+ challenger = spawn_victim(cpu);
+ if (challenger.pid < 0) {
+ SCX_ERR("Failed to spawn enqueue challenger");
+ goto out;
+ }
+ }
+
+ skel = kick__open();
+ if (!skel) {
+ SCX_ERR("Failed to open scenario %u", scenario);
+ goto out;
+ }
+ SCX_ENUM_INIT(skel);
+ skel->rodata->scenario = scenario;
+ skel->rodata->victim_pid = victim.pid;
+ skel->rodata->challenger_pid = challenger.pid;
+ skel->rodata->target_cpu = cpu;
+ skel->rodata->slice_expiry_override = slice_expiry_override;
+ skel->struct_ops.kick_ops->flags |= ops_flags;
+ if (kick__load(skel)) {
+ SCX_ERR("Failed to load scenario %u", scenario);
+ goto out;
+ }
+
+ bpf_map__set_autoattach(skel->maps.kick_ops, false);
+ if (kick__attach(skel)) {
+ SCX_ERR("Failed to attach __resched_curr tracer");
+ goto out;
+ }
+ skel->bss->state = KICK_STATE_ARMED;
+ ops_link = bpf_map__attach_struct_ops(skel->maps.kick_ops);
+ if (!ops_link) {
+ SCX_ERR("Failed to attach scenario %u", scenario);
+ goto out;
+ }
+ if (!start_victim(&victim)) {
+ SCX_ERR("Failed to start victim");
+ goto out;
+ }
+ if (scenario == ENQ_BOTH) {
+ if (!wait_for_state(skel, KICK_STATE_QUEUED)) {
+ SCX_ERR("Enqueue scenario did not arm");
+ goto out;
+ }
+ if (!start_victim(&challenger)) {
+ SCX_ERR("Failed to start enqueue challenger");
+ goto out;
+ }
+ }
+ if (!wait_for_state(skel, KICK_STATE_DONE)) {
+ SCX_ERR("Scenario %u stopped in state %u, exit kind %d", scenario, skel->bss->state,
+ skel->data->uei.kind);
+ goto out;
+ }
+
+ obs->slice_before = skel->bss->slice_before;
+ obs->slice_at_resched = skel->bss->slice_at_resched;
+ obs->nr_wait_callbacks = skel->bss->nr_wait_callbacks;
+ obs->resched_tif = skel->bss->resched_tif;
+ ret = SCX_TEST_PASS;
+out:
+ stop_victim(&challenger);
+ stop_victim(&victim);
+ if (ops_link)
+ bpf_link__destroy(ops_link);
+ if (skel)
+ kick__destroy(skel);
+ return ret;
+}
+
+static bool observation_valid(const struct observation *obs)
+{
+ return obs->slice_before > 0 && !obs->slice_at_resched;
+}
+
+static int active_lazy_mode(void)
+{
+ char buf[128];
+ FILE *file;
+
+ file = fopen("/sys/kernel/debug/sched/preempt", "r");
+ if (!file) {
+#if defined(CONFIG_PREEMPT_LAZY) && !defined(CONFIG_PREEMPT_DYNAMIC)
+ return 1;
+#else
+ return -1;
+#endif
+ }
+ if (!fgets(buf, sizeof(buf), file)) {
+ fclose(file);
+ return -1;
+ }
+ fclose(file);
+
+ if (strstr(buf, "(lazy)"))
+ return 1;
+ if (strstr(buf, "(full)"))
+ return 0;
+ return -1;
+}
+
+static enum scx_test_status setup_immediate(void **ctx)
+{
+ if (!enum_supported("scx_kick_flags", "SCX_KICK_PREEMPT")) {
+ printf("SKIP: SCX_KICK_PREEMPT is not supported\n");
+ return SCX_TEST_SKIP;
+ }
+ return setup_controller(ctx);
+}
+
+static enum scx_test_status setup_lazy(void **ctx)
+{
+ if (!enum_supported("scx_kick_flags", "SCX_KICK_PREEMPT_LAZY")) {
+ printf("SKIP: SCX_KICK_PREEMPT_LAZY is not supported\n");
+ return SCX_TEST_SKIP;
+ }
+ return setup_immediate(ctx);
+}
+
+static enum scx_test_status setup_tick(void **ctx)
+{
+ if (!enum_supported("scx_ops_flags", "SCX_OPS_LAZY_SLICE_EXPIRY")) {
+ printf("SKIP: SCX_OPS_LAZY_SLICE_EXPIRY is not supported\n");
+ return SCX_TEST_SKIP;
+ }
+ return setup_lazy(ctx);
+}
+
+static enum scx_test_status setup_coalesce(void **ctx)
+{
+ if (!enum_supported("scx_enq_flags", "SCX_ENQ_PREEMPT_LAZY")) {
+ printf("SKIP: SCX_ENQ_PREEMPT_LAZY is not supported\n");
+ return SCX_TEST_SKIP;
+ }
+ return setup_lazy(ctx);
+}
+
+static enum scx_test_status setup_invalid(void **ctx)
+{
+ return setup_lazy(ctx);
+}
+
+static enum scx_test_status run_immediate(void *ctx)
+{
+ struct observation obs;
+ enum scx_test_status status;
+
+ status = trace_one(ctx, KICK_IMMEDIATE, 0, -1, &obs);
+ SCX_EQ(status, SCX_TEST_PASS);
+ SCX_ASSERT(observation_valid(&obs));
+ return SCX_TEST_PASS;
+}
+
+static enum scx_test_status run_lazy(void *ctx)
+{
+ struct observation immediate, lazy;
+ enum scx_test_status status;
+ int lazy_mode;
+
+ status = trace_one(ctx, KICK_IMMEDIATE, 0, -1, &immediate);
+ SCX_EQ(status, SCX_TEST_PASS);
+ SCX_ASSERT(observation_valid(&immediate));
+ status = trace_one(ctx, KICK_LAZY, 0, -1, &lazy);
+ SCX_EQ(status, SCX_TEST_PASS);
+ SCX_ASSERT(observation_valid(&lazy));
+
+ lazy_mode = active_lazy_mode();
+ if (lazy_mode > 0)
+ SCX_FAIL_IF(lazy.resched_tif == immediate.resched_tif,
+ "Lazy mode used immediate TIF %d", lazy.resched_tif);
+ else if (!lazy_mode)
+ SCX_EQ(lazy.resched_tif, immediate.resched_tif);
+ else
+ printf("INFO: preemption mode unavailable; lazy TIF was %d, immediate TIF was %d\n",
+ lazy.resched_tif, immediate.resched_tif);
+
+ return SCX_TEST_PASS;
+}
+
+static enum scx_test_status run_coalesce(void *ctx)
+{
+ struct observation immediate, lazy_first, immediate_first;
+ struct observation plain_first, lazy_then_plain;
+ struct observation both, lazy_wait, enq_both;
+ enum scx_test_status status;
+
+ status = trace_one(ctx, KICK_IMMEDIATE, 0, -1, &immediate);
+ SCX_EQ(status, SCX_TEST_PASS);
+ SCX_ASSERT(observation_valid(&immediate));
+ status = trace_one(ctx, KICK_LAZY_THEN_IMMEDIATE, 0, -1,
+ &lazy_first);
+ SCX_EQ(status, SCX_TEST_PASS);
+ SCX_ASSERT(observation_valid(&lazy_first));
+ status = trace_one(ctx, KICK_IMMEDIATE_THEN_LAZY, 0, -1,
+ &immediate_first);
+ SCX_EQ(status, SCX_TEST_PASS);
+ SCX_ASSERT(observation_valid(&immediate_first));
+ SCX_EQ(lazy_first.resched_tif, immediate.resched_tif);
+ SCX_EQ(immediate_first.resched_tif, immediate.resched_tif);
+
+ /*
+ * A plain kick in the same batch doesn't clear the slice by itself.
+ * The lazy preemption must still expire it, and the plain kick must
+ * still reschedule immediately, whichever came first.
+ */
+ status = trace_one(ctx, KICK_PLAIN_THEN_LAZY, 0, -1,
+ &plain_first);
+ SCX_EQ(status, SCX_TEST_PASS);
+ SCX_ASSERT(observation_valid(&plain_first));
+ status = trace_one(ctx, KICK_LAZY_THEN_PLAIN, 0, -1,
+ &lazy_then_plain);
+ SCX_EQ(status, SCX_TEST_PASS);
+ SCX_ASSERT(observation_valid(&lazy_then_plain));
+ SCX_EQ(plain_first.resched_tif, immediate.resched_tif);
+ SCX_EQ(lazy_then_plain.resched_tif, immediate.resched_tif);
+
+ /* Immediate kick and WAIT both take precedence over lazy preemption. */
+ status = trace_one(ctx, KICK_BOTH, 0, -1, &both);
+ SCX_EQ(status, SCX_TEST_PASS);
+ SCX_ASSERT(observation_valid(&both));
+ status = trace_one(ctx, KICK_LAZY_WAIT, 0, -1, &lazy_wait);
+ SCX_EQ(status, SCX_TEST_PASS);
+ SCX_ASSERT(observation_valid(&lazy_wait));
+ SCX_EQ(both.resched_tif, immediate.resched_tif);
+ SCX_EQ(lazy_wait.resched_tif, immediate.resched_tif);
+ SCX_GT(lazy_wait.nr_wait_callbacks, 0);
+
+ /* Immediate enqueue preemption likewise takes precedence over lazy. */
+ status = trace_one(ctx, ENQ_BOTH, 0, -1, &enq_both);
+ SCX_EQ(status, SCX_TEST_PASS);
+ SCX_ASSERT(observation_valid(&enq_both));
+ SCX_EQ(enq_both.resched_tif, immediate.resched_tif);
+ return SCX_TEST_PASS;
+}
+
+/*
+ * A slice running out at the tick reschedules immediately by default and
+ * lazily with SCX_OPS_LAZY_SLICE_EXPIRY, the way fair.c expires a slice.
+ */
+static enum scx_test_status run_tick(void *ctx)
+{
+ struct observation immediate, lazy, force_lazy, force_immediate;
+ enum scx_test_status status;
+ u64 lazy_flag;
+ int lazy_mode;
+ bool found;
+
+ found = __COMPAT_read_enum("scx_ops_flags", "SCX_OPS_LAZY_SLICE_EXPIRY",
+ &lazy_flag);
+ SCX_ASSERT(found);
+ status = trace_one(ctx, TICK_EXPIRY, 0, -1, &immediate);
+ SCX_EQ(status, SCX_TEST_PASS);
+ SCX_ASSERT(observation_valid(&immediate));
+ status = trace_one(ctx, TICK_EXPIRY, lazy_flag, -1, &lazy);
+ SCX_EQ(status, SCX_TEST_PASS);
+ SCX_ASSERT(observation_valid(&lazy));
+ status = trace_one(ctx, TICK_EXPIRY, 0, 1, &force_lazy);
+ SCX_EQ(status, SCX_TEST_PASS);
+ SCX_ASSERT(observation_valid(&force_lazy));
+ status = trace_one(ctx, TICK_EXPIRY, lazy_flag, 0,
+ &force_immediate);
+ SCX_EQ(status, SCX_TEST_PASS);
+ SCX_ASSERT(observation_valid(&force_immediate));
+
+ lazy_mode = active_lazy_mode();
+ if (lazy_mode > 0)
+ SCX_FAIL_IF(lazy.resched_tif == immediate.resched_tif,
+ "Lazy slice expiry used immediate TIF %d", lazy.resched_tif);
+ else if (!lazy_mode)
+ SCX_EQ(lazy.resched_tif, immediate.resched_tif);
+ else
+ printf("INFO: preemption mode unavailable; lazy TIF was %d, immediate TIF was %d\n",
+ lazy.resched_tif, immediate.resched_tif);
+ SCX_EQ(force_lazy.resched_tif, lazy.resched_tif);
+ SCX_EQ(force_immediate.resched_tif, immediate.resched_tif);
+
+ return SCX_TEST_PASS;
+}
+
+static enum scx_test_status invalid_one(struct kick_ctx *ctx, u32 scenario)
+{
+ struct bpf_link *ops_link = NULL;
+ struct kick *skel = NULL;
+ struct victim victim;
+ enum scx_test_status ret = SCX_TEST_FAIL;
+ int cpu = ctx->target_cpu;
+ int i;
+
+ victim = spawn_victim(cpu);
+ if (victim.pid < 0)
+ return SCX_TEST_FAIL;
+
+ skel = kick__open();
+ if (!skel)
+ goto out;
+ SCX_ENUM_INIT(skel);
+ skel->rodata->scenario = scenario;
+ if (kick__load(skel))
+ goto out;
+ ops_link = bpf_map__attach_struct_ops(skel->maps.kick_ops);
+ if (!ops_link || !start_victim(&victim))
+ goto out;
+
+ for (i = 0; i < WAIT_LOOPS; i++) {
+ if (skel->data->uei.kind == EXIT_KIND(SCX_EXIT_ERROR)) {
+ ret = SCX_TEST_PASS;
+ break;
+ }
+ usleep(1000);
+ }
+out:
+ stop_victim(&victim);
+ if (ops_link)
+ bpf_link__destroy(ops_link);
+ if (skel)
+ kick__destroy(skel);
+ return ret;
+}
+
+static enum scx_test_status run_invalid(void *ctx)
+{
+ enum scx_test_status status;
+ u32 scenario;
+
+ for (scenario = INVALID_KICK_IDLE;
+ scenario <= INVALID_KICK_UNKNOWN; scenario++) {
+ status = invalid_one(ctx, scenario);
+ SCX_EQ(status, SCX_TEST_PASS);
+ }
+ return SCX_TEST_PASS;
+}
+
+static struct scx_test kick_immediate = {
+ .name = "kick_immediate",
+ .description = "Trace immediate kick slice expiration and rescheduling",
+ .setup = setup_immediate,
+ .run = run_immediate,
+ .cleanup = cleanup_controller,
+};
+
+static struct scx_test kick_lazy = {
+ .name = "kick_lazy",
+ .description = "Trace lazy kick slice expiration and rescheduling",
+ .setup = setup_lazy,
+ .run = run_lazy,
+ .cleanup = cleanup_controller,
+};
+
+static struct scx_test kick_coalesce = {
+ .name = "kick_coalesce",
+ .description = "Verify lazy preemption coalesces with immediate requests",
+ .setup = setup_coalesce,
+ .run = run_coalesce,
+ .cleanup = cleanup_controller,
+};
+
+static struct scx_test kick_tick = {
+ .name = "kick_tick",
+ .description = "Trace slice expiry at the tick, immediate and lazy",
+ .setup = setup_tick,
+ .run = run_tick,
+ .cleanup = cleanup_controller,
+};
+
+static struct scx_test kick_invalid = {
+ .name = "kick_invalid",
+ .description = "Verify invalid kick flag combinations fail",
+ .setup = setup_invalid,
+ .run = run_invalid,
+ .cleanup = cleanup_controller,
+};
+
+__attribute__((constructor))
+static void register_kick_tests(void)
+{
+ scx_test_register(&kick_immediate);
+ scx_test_register(&kick_lazy);
+ scx_test_register(&kick_coalesce);
+ scx_test_register(&kick_tick);
+ scx_test_register(&kick_invalid);
+}
diff --git a/tools/testing/selftests/sched_ext/nohz_tick.bpf.c b/tools/testing/selftests/sched_ext/nohz_tick.bpf.c
index 6998c5dd6bcb9..96ba1524ca384 100644
--- a/tools/testing/selftests/sched_ext/nohz_tick.bpf.c
+++ b/tools/testing/selftests/sched_ext/nohz_tick.bpf.c
@@ -9,10 +9,23 @@
char _license[] SEC("license") = "GPL";
const volatile s32 test_cpu;
-bool finite_phase;
+enum nohz_phase {
+ NOHZ_PHASE_INF,
+ NOHZ_PHASE_FINITE,
+ NOHZ_PHASE_LAZY_ENQ,
+ NOHZ_PHASE_LAZY_KICK,
+};
+
+u32 phase;
+s32 victim_pid;
+s32 challenger_pid;
+s32 trigger_pid;
u64 nr_inf_running;
u64 nr_finite_running;
u64 nr_finite_ticks;
+u64 nr_lazy_victim_running;
+u64 nr_lazy_enq_running;
+u64 nr_lazy_kick_running;
UEI_DEFINE(uei);
@@ -24,9 +37,31 @@ s32 BPF_STRUCT_OPS(nohz_tick_select_cpu, struct task_struct *p, s32 prev_cpu,
void BPF_STRUCT_OPS(nohz_tick_enqueue, struct task_struct *p, u64 enq_flags)
{
- u64 slice = finite_phase ? 1000000ULL : SCX_SLICE_INF;
+ u64 slice;
+ u64 dsq_id = SCX_DSQ_GLOBAL;
+
+ switch (phase) {
+ case NOHZ_PHASE_INF:
+ slice = SCX_SLICE_INF;
+ break;
+ case NOHZ_PHASE_FINITE:
+ slice = 1000000ULL;
+ break;
+ case NOHZ_PHASE_LAZY_ENQ:
+ case NOHZ_PHASE_LAZY_KICK:
+ dsq_id = SCX_DSQ_LOCAL;
+ slice = p->pid == victim_pid ? SCX_SLICE_INF : SCX_SLICE_DFL;
+ if (phase == NOHZ_PHASE_LAZY_ENQ && p->pid == challenger_pid)
+ enq_flags |= SCX_ENQ_PREEMPT_LAZY;
+ break;
+ default:
+ slice = SCX_SLICE_DFL;
+ break;
+ }
- scx_bpf_dsq_insert(p, SCX_DSQ_GLOBAL, slice, enq_flags);
+ scx_bpf_dsq_insert(p, dsq_id, slice, enq_flags);
+ if (phase == NOHZ_PHASE_LAZY_KICK && p->pid == trigger_pid)
+ scx_bpf_kick_cpu(test_cpu, SCX_KICK_PREEMPT_LAZY);
if (enq_flags & SCX_ENQ_LAST)
scx_bpf_kick_cpu(test_cpu, SCX_KICK_IDLE);
}
@@ -36,15 +71,22 @@ void BPF_STRUCT_OPS(nohz_tick_running, struct task_struct *p)
if (bpf_get_smp_processor_id() != test_cpu)
return;
- if (finite_phase)
+ if (phase == NOHZ_PHASE_FINITE)
__sync_fetch_and_add(&nr_finite_running, 1);
- else
+ else if (phase == NOHZ_PHASE_INF)
__sync_fetch_and_add(&nr_inf_running, 1);
+ else if (p->pid == victim_pid)
+ __sync_fetch_and_add(&nr_lazy_victim_running, 1);
+ else if (phase == NOHZ_PHASE_LAZY_ENQ && p->pid == challenger_pid)
+ __sync_fetch_and_add(&nr_lazy_enq_running, 1);
+ else if (phase == NOHZ_PHASE_LAZY_KICK && p->pid == challenger_pid)
+ __sync_fetch_and_add(&nr_lazy_kick_running, 1);
}
void BPF_STRUCT_OPS(nohz_tick_tick, struct task_struct *p)
{
- if (bpf_get_smp_processor_id() == test_cpu && finite_phase)
+ if (bpf_get_smp_processor_id() == test_cpu &&
+ phase == NOHZ_PHASE_FINITE)
__sync_fetch_and_add(&nr_finite_ticks, 1);
}
@@ -61,5 +103,5 @@ struct sched_ext_ops nohz_tick_ops = {
.tick = (void *)nohz_tick_tick,
.exit = (void *)nohz_tick_exit,
.name = "nohz_tick",
- .timeout_ms = 1000U,
+ .timeout_ms = 5000U,
};
diff --git a/tools/testing/selftests/sched_ext/nohz_tick.c b/tools/testing/selftests/sched_ext/nohz_tick.c
index 028f54391c2ca..acc6510e239ad 100644
--- a/tools/testing/selftests/sched_ext/nohz_tick.c
+++ b/tools/testing/selftests/sched_ext/nohz_tick.c
@@ -28,12 +28,26 @@
#endif
#define MIN_FINITE_TICKS 3
-#define PHASE_TIMEOUT_MS 1000
+#define PHASE_TIMEOUT_MS 5000
struct nohz_tick_ctx {
struct nohz_tick *skel;
cpu_set_t original_mask;
int test_cpu;
+ int housekeeping_cpu;
+ bool lazy_supported;
+};
+
+enum nohz_phase {
+ NOHZ_PHASE_INF,
+ NOHZ_PHASE_FINITE,
+ NOHZ_PHASE_LAZY_ENQ,
+ NOHZ_PHASE_LAZY_KICK,
+};
+
+struct gated_worker {
+ pid_t pid;
+ int start_fd;
};
static int first_allowed_cpu(const cpu_set_t *mask, int first, int last)
@@ -47,20 +61,21 @@ static int first_allowed_cpu(const cpu_set_t *mask, int first, int last)
return -1;
}
-static int find_nohz_full_cpu(const cpu_set_t *allowed)
+static int read_nohz_full_mask(cpu_set_t *mask)
{
char buf[4096], *cur, *end;
FILE *file;
+ int ret = 0;
file = fopen("/sys/devices/system/cpu/nohz_full", "r");
if (!file)
- return -1;
+ return -errno;
if (!fgets(buf, sizeof(buf), file)) {
- fclose(file);
- return -1;
+ ret = ferror(file) ? -errno : -EINVAL;
+ goto out;
}
- fclose(file);
+ CPU_ZERO(mask);
cur = buf;
while (*cur) {
long first, last;
@@ -73,25 +88,30 @@ static int find_nohz_full_cpu(const cpu_set_t *allowed)
errno = 0;
first = strtol(cur, &end, 10);
- if (errno || end == cur || first < 0 || first >= CPU_SETSIZE)
- return -1;
+ if (errno || end == cur || first < 0 || first >= CPU_SETSIZE) {
+ ret = -EINVAL;
+ goto out;
+ }
cur = end;
last = first;
if (*cur == '-') {
cur++;
errno = 0;
last = strtol(cur, &end, 10);
- if (errno || end == cur || last < first)
- return -1;
+ if (errno || end == cur || last < first) {
+ ret = -EINVAL;
+ goto out;
+ }
cur = end;
}
- cpu = first_allowed_cpu(allowed, first, last);
- if (cpu >= 0)
- return cpu;
+ for (cpu = first; cpu <= last && cpu < CPU_SETSIZE; cpu++)
+ CPU_SET(cpu, mask);
}
- return -1;
+out:
+ fclose(file);
+ return ret;
}
static pid_t start_worker(int cpu)
@@ -132,6 +152,87 @@ static void stop_worker(pid_t pid)
waitpid(pid, NULL, 0);
}
+static struct gated_worker spawn_gated_worker(int cpu)
+{
+ struct gated_worker worker = { .pid = -1, .start_fd = -1 };
+ int ready[2], start[2];
+ pid_t parent = getpid();
+ char byte = 1;
+
+ if (pipe(ready))
+ return worker;
+ if (pipe(start)) {
+ close(ready[0]);
+ close(ready[1]);
+ return worker;
+ }
+
+ worker.pid = fork();
+ if (!worker.pid) {
+ struct sched_param param = {};
+ cpu_set_t mask;
+
+ close(ready[0]);
+ close(start[1]);
+ if (prctl(PR_SET_PDEATHSIG, SIGKILL) || getppid() != parent)
+ _exit(1);
+ CPU_ZERO(&mask);
+ CPU_SET(cpu, &mask);
+ if (sched_setaffinity(0, sizeof(mask), &mask))
+ _exit(1);
+ if (sched_setscheduler(0, SCHED_EXT, ¶m))
+ _exit(1);
+ if (write(ready[1], &byte, 1) != 1)
+ _exit(1);
+ close(ready[1]);
+ if (read(start[0], &byte, 1) != 1)
+ _exit(1);
+ close(start[0]);
+ for (;;)
+ asm volatile("" ::: "memory");
+ }
+ if (worker.pid < 0) {
+ close(ready[0]);
+ close(ready[1]);
+ close(start[0]);
+ close(start[1]);
+ return worker;
+ }
+
+ close(ready[1]);
+ close(start[0]);
+ if (read(ready[0], &byte, 1) != 1) {
+ close(ready[0]);
+ close(start[1]);
+ kill(worker.pid, SIGKILL);
+ waitpid(worker.pid, NULL, 0);
+ worker.pid = -1;
+ return worker;
+ }
+ close(ready[0]);
+ worker.start_fd = start[1];
+ return worker;
+}
+
+static bool start_gated_worker(struct gated_worker *worker)
+{
+ char byte = 1;
+
+ if (write(worker->start_fd, &byte, 1) != 1)
+ return false;
+ close(worker->start_fd);
+ worker->start_fd = -1;
+ return true;
+}
+
+static void stop_gated_worker(struct gated_worker *worker)
+{
+ if (worker->start_fd >= 0)
+ close(worker->start_fd);
+ stop_worker(worker->pid);
+ worker->pid = -1;
+}
+
static int pause_worker(pid_t pid)
{
int status;
@@ -162,8 +263,9 @@ static bool wait_for_counter(const u64 *counter, u64 value, int timeout_ms)
static enum scx_test_status setup(void **ctx_ptr)
{
struct nohz_tick_ctx *ctx;
- cpu_set_t controller_mask;
- int cpu;
+ cpu_set_t controller_mask, nohz_full_mask;
+ u64 enum_value;
+ int cpu, i, ret;
ctx = calloc(1, sizeof(*ctx));
SCX_FAIL_IF(!ctx, "Failed to allocate context");
@@ -173,15 +275,27 @@ static enum scx_test_status setup(void **ctx_ptr)
SCX_FAIL("Failed to get affinity (%d)", errno);
}
- cpu = find_nohz_full_cpu(&ctx->original_mask);
- if (cpu < 0) {
+ ret = read_nohz_full_mask(&nohz_full_mask);
+ if (ret) {
+ fprintf(stderr, "SKIP: failed to read NOHZ_FULL mask (%d)\n", ret);
+ free(ctx);
+ return SCX_TEST_SKIP;
+ }
+
+ for (cpu = 0; cpu < CPU_SETSIZE; cpu++)
+ if (CPU_ISSET(cpu, &ctx->original_mask) &&
+ CPU_ISSET(cpu, &nohz_full_mask))
+ break;
+ if (cpu == CPU_SETSIZE) {
fprintf(stderr, "SKIP: no allowed NOHZ_FULL CPU\n");
free(ctx);
return SCX_TEST_SKIP;
}
controller_mask = ctx->original_mask;
- CPU_CLR(cpu, &controller_mask);
+ for (i = 0; i < CPU_SETSIZE; i++)
+ if (CPU_ISSET(i, &nohz_full_mask))
+ CPU_CLR(i, &controller_mask);
if (CPU_COUNT(&controller_mask) == 0) {
fprintf(stderr, "SKIP: no housekeeping CPU available\n");
free(ctx);
@@ -189,6 +303,13 @@ static enum scx_test_status setup(void **ctx_ptr)
}
ctx->test_cpu = cpu;
+ ctx->housekeeping_cpu = first_allowed_cpu(&controller_mask, 0,
+ CPU_SETSIZE - 1);
+ ctx->lazy_supported =
+ __COMPAT_read_enum("scx_enq_flags", "SCX_ENQ_PREEMPT_LAZY",
+ &enum_value) &&
+ __COMPAT_read_enum("scx_kick_flags", "SCX_KICK_PREEMPT_LAZY",
+ &enum_value);
ctx->skel = nohz_tick__open();
if (!ctx->skel) {
free(ctx);
@@ -220,11 +341,15 @@ static enum scx_test_status run(void *ctx_ptr)
struct nohz_tick_ctx *ctx = ctx_ptr;
struct nohz_tick *skel = ctx->skel;
struct bpf_link *link = NULL;
+ struct gated_worker victim = { .pid = -1, .start_fd = -1 };
+ struct gated_worker challenger = { .pid = -1, .start_fd = -1 };
+ struct gated_worker trigger = { .pid = -1, .start_fd = -1 };
enum scx_test_status status = SCX_TEST_FAIL;
pid_t finite_worker = -1;
pid_t inf_worker = -1;
u64 finite_running;
u64 finite_ticks;
+ u64 victim_running;
int ret;
link = bpf_map__attach_struct_ops(skel->maps.nohz_tick_ops);
@@ -260,7 +385,8 @@ static enum scx_test_status run(void *ctx_ptr)
/*
* The next EXT task receives a finite slice and must restart the tick.
*/
- __atomic_store_n(&skel->bss->finite_phase, true, __ATOMIC_RELEASE);
+ __atomic_store_n(&skel->bss->phase, NOHZ_PHASE_FINITE,
+ __ATOMIC_RELEASE);
finite_worker = start_worker(ctx->test_cpu);
if (finite_worker < 0) {
SCX_ERR("Failed to start finite-slice worker (%d)", errno);
@@ -308,7 +434,87 @@ static enum scx_test_status run(void *ctx_ptr)
finite_ticks));
goto out;
}
+ stop_worker(finite_worker);
+ finite_worker = -1;
+ stop_worker(inf_worker);
+ inf_worker = -1;
+ if (!ctx->lazy_supported)
+ goto check_exit;
+
+ /*
+ * A lazy local enqueue must restart the tick after clearing the slice of
+ * an infinite-slice task on a full-dynticks CPU.
+ */
+ __atomic_store_n(&skel->bss->phase, NOHZ_PHASE_LAZY_ENQ,
+ __ATOMIC_RELEASE);
+ victim = spawn_gated_worker(ctx->test_cpu);
+ challenger = spawn_gated_worker(ctx->test_cpu);
+ if (victim.pid < 0 || challenger.pid < 0) {
+ SCX_ERR("Failed to spawn lazy-enqueue workers");
+ goto out;
+ }
+ skel->bss->victim_pid = victim.pid;
+ skel->bss->challenger_pid = challenger.pid;
+ if (!start_gated_worker(&victim) ||
+ !wait_for_counter(&skel->bss->nr_lazy_victim_running, 1,
+ PHASE_TIMEOUT_MS)) {
+ SCX_ERR("Lazy-enqueue victim was not scheduled");
+ goto out;
+ }
+ usleep(100000);
+
+ if (!start_gated_worker(&challenger) ||
+ !wait_for_counter(&skel->bss->nr_lazy_enq_running, 1,
+ PHASE_TIMEOUT_MS)) {
+ SCX_ERR("Lazy enqueue made no progress on CPU %d", ctx->test_cpu);
+ goto out;
+ }
+ stop_gated_worker(&challenger);
+ stop_gated_worker(&victim);
+
+ /* Repeat with a lazy kick delivered from a housekeeping CPU. */
+ __atomic_store_n(&skel->bss->phase, NOHZ_PHASE_LAZY_KICK,
+ __ATOMIC_RELEASE);
+ victim = spawn_gated_worker(ctx->test_cpu);
+ challenger = spawn_gated_worker(ctx->test_cpu);
+ trigger = spawn_gated_worker(ctx->housekeeping_cpu);
+ if (victim.pid < 0 || challenger.pid < 0 || trigger.pid < 0) {
+ SCX_ERR("Failed to spawn lazy-kick workers");
+ goto out;
+ }
+ skel->bss->victim_pid = victim.pid;
+ skel->bss->challenger_pid = challenger.pid;
+ skel->bss->trigger_pid = trigger.pid;
+ victim_running = __atomic_load_n(&skel->bss->nr_lazy_victim_running,
+ __ATOMIC_RELAXED);
+ if (!start_gated_worker(&victim) ||
+ !wait_for_counter(&skel->bss->nr_lazy_victim_running,
+ victim_running + 1,
+ PHASE_TIMEOUT_MS)) {
+ SCX_ERR("Lazy-kick victim was not scheduled");
+ goto out;
+ }
+ if (!start_gated_worker(&challenger)) {
+ SCX_ERR("Failed to start lazy-kick challenger");
+ goto out;
+ }
+ usleep(100000);
+ if (__atomic_load_n(&skel->bss->nr_lazy_kick_running,
+ __ATOMIC_RELAXED)) {
+ SCX_ERR("Lazy-kick challenger ran before the kick");
+ goto out;
+ }
+ if (!start_gated_worker(&trigger) ||
+ !wait_for_counter(&skel->bss->nr_lazy_kick_running, 1,
+ PHASE_TIMEOUT_MS)) {
+ SCX_ERR("Lazy kick made no progress on CPU %d", ctx->test_cpu);
+ goto out;
+ }
+ stop_gated_worker(&trigger);
+ stop_gated_worker(&challenger);
+ stop_gated_worker(&victim);
+check_exit:
if (skel->data->uei.kind != EXIT_KIND(SCX_EXIT_NONE)) {
SCX_ERR("Scheduler exited unexpectedly (kind=%llu code=%lld)",
(unsigned long long)skel->data->uei.kind,
@@ -321,6 +527,9 @@ static enum scx_test_status run(void *ctx_ptr)
(unsigned long long)skel->bss->nr_finite_ticks);
status = SCX_TEST_PASS;
out:
+ stop_gated_worker(&trigger);
+ stop_gated_worker(&challenger);
+ stop_gated_worker(&victim);
stop_worker(finite_worker);
stop_worker(inf_worker);
if (link)
--
2.55.0
^ permalink raw reply [flat|nested] 8+ messages in thread
* [PATCH 2/2] selftests/sched_ext: Add lazy preemption tests
2026-09-15 9:00 [PATCHSET v4 sched_ext/for-7.4] sched_ext: Add lazy preemption support Andrea Righi
@ 2026-09-15 9:00 ` Andrea Righi
0 siblings, 0 replies; 8+ messages in thread
From: Andrea Righi @ 2026-09-15 9:00 UTC (permalink / raw)
To: Tejun Heo, David Vernet, Changwoo Min
Cc: Emil Tsalapatis, sched-ext, linux-kernel
Add trace-based coverage for immediate and lazy preemption. An fexit
probe on __resched_curr() records the requested TIF and the current task
slice, while the stopping callback verifies that the task reaches a
scheduling boundary.
Exercise kick requests individually, in both orders and combined in one
call. Verify that immediate preemption and WAIT take precedence over
lazy preemption, and that combining immediate and lazy enqueue
preemption follows the same rule. Also test overriding the expiry
default in both directions through scx_bpf_task_set_slice_expiry().
Extend the NO_HZ_FULL test with infinite-slice victims. Verify that lazy
enqueue and kick requests restart a stopped tick and make forward
progress. Keep invalid kick flag coverage and skip modes not exposed by
the running kernel.
Signed-off-by: Andrea Righi <arighi@nvidia.com>
---
tools/testing/selftests/sched_ext/Makefile | 1 +
tools/testing/selftests/sched_ext/kick.bpf.c | 182 ++++++
tools/testing/selftests/sched_ext/kick.c | 608 ++++++++++++++++++
.../selftests/sched_ext/nohz_tick.bpf.c | 56 +-
tools/testing/selftests/sched_ext/nohz_tick.c | 249 ++++++-
5 files changed, 1069 insertions(+), 27 deletions(-)
create mode 100644 tools/testing/selftests/sched_ext/kick.bpf.c
create mode 100644 tools/testing/selftests/sched_ext/kick.c
diff --git a/tools/testing/selftests/sched_ext/Makefile b/tools/testing/selftests/sched_ext/Makefile
index 5f5dd9ab903ae..c4ec9b21a4c2a 100644
--- a/tools/testing/selftests/sched_ext/Makefile
+++ b/tools/testing/selftests/sched_ext/Makefile
@@ -172,6 +172,7 @@ auto-test-targets := \
exit \
hotplug \
init_enable_count \
+ kick \
maximal \
maybe_null \
minimal \
diff --git a/tools/testing/selftests/sched_ext/kick.bpf.c b/tools/testing/selftests/sched_ext/kick.bpf.c
new file mode 100644
index 0000000000000..5a64e19246004
--- /dev/null
+++ b/tools/testing/selftests/sched_ext/kick.bpf.c
@@ -0,0 +1,182 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (c) 2026 NVIDIA CORPORATION & AFFILIATES
+ */
+#include <scx/common.bpf.h>
+
+char _license[] SEC("license") = "GPL";
+
+enum kick_scenario {
+ KICK_IMMEDIATE,
+ KICK_LAZY,
+ KICK_LAZY_THEN_IMMEDIATE,
+ KICK_IMMEDIATE_THEN_LAZY,
+ KICK_PLAIN_THEN_LAZY,
+ KICK_LAZY_THEN_PLAIN,
+ KICK_BOTH,
+ KICK_LAZY_WAIT,
+ ENQ_BOTH,
+ TICK_EXPIRY,
+ INVALID_KICK_IDLE,
+ INVALID_KICK_UNKNOWN,
+};
+
+enum kick_state {
+ KICK_STATE_IDLE,
+ KICK_STATE_ARMED,
+ KICK_STATE_QUEUED,
+ KICK_STATE_RESCHED,
+ KICK_STATE_DONE,
+};
+
+const volatile u32 scenario;
+const volatile s32 victim_pid;
+const volatile s32 challenger_pid;
+const volatile s32 target_cpu;
+const volatile s32 slice_expiry_override = -1;
+
+u32 state;
+u64 slice_before;
+u64 slice_at_resched;
+s32 resched_tif;
+u64 nr_wait_callbacks;
+bool enq_preempt_issued;
+
+UEI_DEFINE(uei);
+
+static bool is_trace_scenario(void)
+{
+ return scenario <= TICK_EXPIRY;
+}
+
+void BPF_STRUCT_OPS(kick_enqueue, struct task_struct *p, u64 enq_flags)
+{
+ switch (scenario) {
+ case ENQ_BOTH:
+ if (p->pid == victim_pid) {
+ scx_bpf_dsq_insert(p, SCX_DSQ_GLOBAL, SCX_SLICE_INF,
+ enq_flags);
+ } else if (p->pid == challenger_pid &&
+ state == KICK_STATE_QUEUED) {
+ enq_preempt_issued = true;
+ scx_bpf_dsq_insert(p, SCX_DSQ_LOCAL, SCX_SLICE_DFL,
+ enq_flags | SCX_ENQ_PREEMPT |
+ SCX_ENQ_PREEMPT_LAZY);
+ } else {
+ scx_bpf_dsq_insert(p, SCX_DSQ_GLOBAL, SCX_SLICE_DFL,
+ enq_flags);
+ }
+ return;
+ case INVALID_KICK_IDLE:
+ scx_bpf_kick_cpu(scx_bpf_task_cpu(p), SCX_KICK_PREEMPT_LAZY | SCX_KICK_IDLE);
+ break;
+ case INVALID_KICK_UNKNOWN:
+ scx_bpf_kick_cpu(scx_bpf_task_cpu(p), 1LLU << 63);
+ break;
+ }
+
+ scx_bpf_dsq_insert(p, SCX_DSQ_GLOBAL, SCX_SLICE_DFL, enq_flags);
+}
+
+static void set_slice_expiry_override(struct task_struct *p)
+{
+ if (p->pid == victim_pid && slice_expiry_override >= 0)
+ scx_bpf_task_set_slice_expiry(p, slice_expiry_override);
+}
+
+void BPF_STRUCT_OPS(kick_running, struct task_struct *p)
+{
+ if (!is_trace_scenario() || p->pid != victim_pid)
+ return;
+ set_slice_expiry_override(p);
+ if (__sync_val_compare_and_swap(&state, KICK_STATE_ARMED, KICK_STATE_QUEUED) !=
+ KICK_STATE_ARMED)
+ return;
+
+ slice_before = p->scx.slice;
+
+ switch (scenario) {
+ case KICK_IMMEDIATE:
+ scx_bpf_kick_cpu(target_cpu, SCX_KICK_PREEMPT);
+ break;
+ case KICK_LAZY:
+ scx_bpf_kick_cpu(target_cpu, SCX_KICK_PREEMPT_LAZY);
+ break;
+ case KICK_LAZY_THEN_IMMEDIATE:
+ scx_bpf_kick_cpu(target_cpu, SCX_KICK_PREEMPT_LAZY);
+ scx_bpf_kick_cpu(target_cpu, SCX_KICK_PREEMPT);
+ break;
+ case KICK_IMMEDIATE_THEN_LAZY:
+ scx_bpf_kick_cpu(target_cpu, SCX_KICK_PREEMPT);
+ scx_bpf_kick_cpu(target_cpu, SCX_KICK_PREEMPT_LAZY);
+ break;
+ case KICK_PLAIN_THEN_LAZY:
+ scx_bpf_kick_cpu(target_cpu, 0);
+ scx_bpf_kick_cpu(target_cpu, SCX_KICK_PREEMPT_LAZY);
+ break;
+ case KICK_LAZY_THEN_PLAIN:
+ scx_bpf_kick_cpu(target_cpu, SCX_KICK_PREEMPT_LAZY);
+ scx_bpf_kick_cpu(target_cpu, 0);
+ break;
+ case KICK_BOTH:
+ scx_bpf_kick_cpu(target_cpu, SCX_KICK_PREEMPT |
+ SCX_KICK_PREEMPT_LAZY);
+ break;
+ case KICK_LAZY_WAIT:
+ scx_bpf_kick_cpu(target_cpu, SCX_KICK_PREEMPT_LAZY |
+ SCX_KICK_WAIT);
+ break;
+ case ENQ_BOTH:
+ /* The userspace controller wakes a competing task. */
+ break;
+ case TICK_EXPIRY:
+ /* no kick: the slice runs out at the tick */
+ break;
+ }
+}
+
+SEC("fexit/__resched_curr")
+int BPF_PROG(kick_need_resched, struct rq *rq, int tif)
+{
+ struct task_struct *task = BPF_CORE_READ(rq, curr);
+
+ if (!task || BPF_CORE_READ(task, pid) != victim_pid ||
+ BPF_CORE_READ(rq, cpu) != target_cpu || state != KICK_STATE_QUEUED)
+ return 0;
+ if (scenario == ENQ_BOTH && !enq_preempt_issued)
+ return 0;
+
+ slice_at_resched = BPF_CORE_READ(task, scx.slice);
+ resched_tif = tif;
+ state = KICK_STATE_RESCHED;
+ return 0;
+}
+
+SEC("fentry/kick_sync_wait_bal_cb")
+int BPF_PROG(kick_wait_callback, struct rq *rq)
+{
+ if (scenario == KICK_LAZY_WAIT &&
+ BPF_CORE_READ(rq, cpu) == target_cpu)
+ __sync_fetch_and_add(&nr_wait_callbacks, 1);
+ return 0;
+}
+
+void BPF_STRUCT_OPS(kick_stopping, struct task_struct *p, bool runnable)
+{
+ if (p->pid == victim_pid && state == KICK_STATE_RESCHED)
+ state = KICK_STATE_DONE;
+}
+
+void BPF_STRUCT_OPS(kick_exit, struct scx_exit_info *ei)
+{
+ UEI_RECORD(uei, ei);
+}
+
+SEC(".struct_ops.link")
+struct sched_ext_ops kick_ops = {
+ .enqueue = (void *)kick_enqueue,
+ .running = (void *)kick_running,
+ .stopping = (void *)kick_stopping,
+ .exit = (void *)kick_exit,
+ .name = "kick",
+};
diff --git a/tools/testing/selftests/sched_ext/kick.c b/tools/testing/selftests/sched_ext/kick.c
new file mode 100644
index 0000000000000..bd347c5051814
--- /dev/null
+++ b/tools/testing/selftests/sched_ext/kick.c
@@ -0,0 +1,608 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (c) 2026 NVIDIA CORPORATION & AFFILIATES
+ */
+#define _GNU_SOURCE
+#include <bpf/bpf.h>
+#include <errno.h>
+#include <linux/sched.h>
+#include <sched.h>
+#include <signal.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/prctl.h>
+#include <sys/wait.h>
+#include <unistd.h>
+#include <scx/common.h>
+
+#include "kick.bpf.skel.h"
+#include "scx_test.h"
+
+#define WAIT_LOOPS 3000
+
+enum kick_scenario {
+ KICK_IMMEDIATE,
+ KICK_LAZY,
+ KICK_LAZY_THEN_IMMEDIATE,
+ KICK_IMMEDIATE_THEN_LAZY,
+ KICK_PLAIN_THEN_LAZY,
+ KICK_LAZY_THEN_PLAIN,
+ KICK_BOTH,
+ KICK_LAZY_WAIT,
+ ENQ_BOTH,
+ TICK_EXPIRY,
+ INVALID_KICK_IDLE,
+ INVALID_KICK_UNKNOWN,
+};
+
+enum kick_state {
+ KICK_STATE_IDLE,
+ KICK_STATE_ARMED,
+ KICK_STATE_QUEUED,
+ KICK_STATE_RESCHED,
+ KICK_STATE_DONE,
+};
+
+struct victim {
+ pid_t pid;
+ int start_fd;
+};
+
+struct observation {
+ u64 slice_before;
+ u64 slice_at_resched;
+ u64 nr_wait_callbacks;
+ s32 resched_tif;
+};
+
+struct kick_ctx {
+ cpu_set_t original_mask;
+ int target_cpu;
+};
+
+static bool enum_supported(const char *type, const char *name)
+{
+ u64 value;
+
+ return __COMPAT_read_enum(type, name, &value);
+}
+
+static enum scx_test_status setup_controller(void **ctx_ptr)
+{
+ struct kick_ctx *ctx;
+ cpu_set_t controller_mask;
+ int cpu, controller_cpu = -1;
+
+ ctx = calloc(1, sizeof(*ctx));
+ SCX_FAIL_IF(!ctx, "Failed to allocate context");
+ if (sched_getaffinity(0, sizeof(ctx->original_mask),
+ &ctx->original_mask)) {
+ free(ctx);
+ SCX_FAIL("Failed to get affinity (%d)", errno);
+ }
+
+ for (cpu = 0; cpu < CPU_SETSIZE; cpu++) {
+ if (!CPU_ISSET(cpu, &ctx->original_mask))
+ continue;
+ if (controller_cpu < 0) {
+ controller_cpu = cpu;
+ } else {
+ ctx->target_cpu = cpu;
+ break;
+ }
+ }
+ if (cpu == CPU_SETSIZE) {
+ printf("SKIP: two allowed CPUs are required\n");
+ free(ctx);
+ return SCX_TEST_SKIP;
+ }
+
+ CPU_ZERO(&controller_mask);
+ CPU_SET(controller_cpu, &controller_mask);
+ if (sched_setaffinity(0, sizeof(controller_mask), &controller_mask)) {
+ free(ctx);
+ SCX_FAIL("Failed to pin controller to CPU %d (%d)",
+ controller_cpu, errno);
+ }
+
+ *ctx_ptr = ctx;
+ return SCX_TEST_PASS;
+}
+
+static void cleanup_controller(void *ctx_ptr)
+{
+ struct kick_ctx *ctx = ctx_ptr;
+
+ sched_setaffinity(0, sizeof(ctx->original_mask), &ctx->original_mask);
+ free(ctx);
+}
+
+static struct victim spawn_victim(int cpu)
+{
+ struct victim victim = { .pid = -1, .start_fd = -1 };
+ int ready[2], start[2];
+ pid_t parent = getpid();
+ char byte = 1;
+
+ if (pipe(ready))
+ return victim;
+ if (pipe(start)) {
+ close(ready[0]);
+ close(ready[1]);
+ return victim;
+ }
+
+ victim.pid = fork();
+ if (!victim.pid) {
+ cpu_set_t mask;
+
+ close(ready[0]);
+ close(start[1]);
+ if (prctl(PR_SET_PDEATHSIG, SIGKILL) || getppid() != parent)
+ _exit(1);
+ CPU_ZERO(&mask);
+ CPU_SET(cpu, &mask);
+ if (sched_setaffinity(0, sizeof(mask), &mask))
+ _exit(1);
+ if (write(ready[1], &byte, 1) != 1)
+ _exit(1);
+ close(ready[1]);
+ if (read(start[0], &byte, 1) != 1)
+ _exit(1);
+ close(start[0]);
+ for (;;)
+ asm volatile("" ::: "memory");
+ }
+ if (victim.pid < 0) {
+ close(ready[0]);
+ close(ready[1]);
+ close(start[0]);
+ close(start[1]);
+ return victim;
+ }
+
+ close(ready[1]);
+ close(start[0]);
+ if (read(ready[0], &byte, 1) != 1) {
+ close(ready[0]);
+ close(start[1]);
+ kill(victim.pid, SIGKILL);
+ waitpid(victim.pid, NULL, 0);
+ victim.pid = -1;
+ return victim;
+ }
+ close(ready[0]);
+ victim.start_fd = start[1];
+ return victim;
+}
+
+static void stop_victim(struct victim *victim)
+{
+ if (victim->start_fd >= 0)
+ close(victim->start_fd);
+ if (victim->pid > 0) {
+ kill(victim->pid, SIGKILL);
+ waitpid(victim->pid, NULL, 0);
+ }
+}
+
+static bool start_victim(struct victim *victim)
+{
+ char byte = 1;
+
+ if (write(victim->start_fd, &byte, 1) != 1)
+ return false;
+ close(victim->start_fd);
+ victim->start_fd = -1;
+ return true;
+}
+
+static bool wait_for_state(struct kick *skel, u32 wanted)
+{
+ int i;
+
+ for (i = 0; i < WAIT_LOOPS; i++) {
+ if (__atomic_load_n(&skel->bss->state, __ATOMIC_ACQUIRE) == wanted)
+ return true;
+ if (skel->data->uei.kind != EXIT_KIND(SCX_EXIT_NONE))
+ return false;
+ usleep(1000);
+ }
+ return false;
+}
+
+static enum scx_test_status trace_one(struct kick_ctx *ctx, u32 scenario,
+ u64 ops_flags,
+ s32 slice_expiry_override,
+ struct observation *obs)
+{
+ struct bpf_link *ops_link = NULL;
+ struct kick *skel = NULL;
+ struct victim challenger = { .pid = -1, .start_fd = -1 };
+ struct victim victim;
+ enum scx_test_status ret = SCX_TEST_FAIL;
+ int cpu = ctx->target_cpu;
+
+ victim = spawn_victim(cpu);
+ if (victim.pid < 0) {
+ SCX_ERR("Failed to spawn victim");
+ return SCX_TEST_FAIL;
+ }
+ if (scenario == ENQ_BOTH) {
+ challenger = spawn_victim(cpu);
+ if (challenger.pid < 0) {
+ SCX_ERR("Failed to spawn enqueue challenger");
+ goto out;
+ }
+ }
+
+ skel = kick__open();
+ if (!skel) {
+ SCX_ERR("Failed to open scenario %u", scenario);
+ goto out;
+ }
+ SCX_ENUM_INIT(skel);
+ skel->rodata->scenario = scenario;
+ skel->rodata->victim_pid = victim.pid;
+ skel->rodata->challenger_pid = challenger.pid;
+ skel->rodata->target_cpu = cpu;
+ skel->rodata->slice_expiry_override = slice_expiry_override;
+ skel->struct_ops.kick_ops->flags |= ops_flags;
+ if (kick__load(skel)) {
+ SCX_ERR("Failed to load scenario %u", scenario);
+ goto out;
+ }
+
+ bpf_map__set_autoattach(skel->maps.kick_ops, false);
+ if (kick__attach(skel)) {
+ SCX_ERR("Failed to attach __resched_curr tracer");
+ goto out;
+ }
+ skel->bss->state = KICK_STATE_ARMED;
+ ops_link = bpf_map__attach_struct_ops(skel->maps.kick_ops);
+ if (!ops_link) {
+ SCX_ERR("Failed to attach scenario %u", scenario);
+ goto out;
+ }
+ if (!start_victim(&victim)) {
+ SCX_ERR("Failed to start victim");
+ goto out;
+ }
+ if (scenario == ENQ_BOTH) {
+ if (!wait_for_state(skel, KICK_STATE_QUEUED)) {
+ SCX_ERR("Enqueue scenario did not arm");
+ goto out;
+ }
+ if (!start_victim(&challenger)) {
+ SCX_ERR("Failed to start enqueue challenger");
+ goto out;
+ }
+ }
+ if (!wait_for_state(skel, KICK_STATE_DONE)) {
+ SCX_ERR("Scenario %u stopped in state %u, exit kind %d", scenario, skel->bss->state,
+ skel->data->uei.kind);
+ goto out;
+ }
+
+ obs->slice_before = skel->bss->slice_before;
+ obs->slice_at_resched = skel->bss->slice_at_resched;
+ obs->nr_wait_callbacks = skel->bss->nr_wait_callbacks;
+ obs->resched_tif = skel->bss->resched_tif;
+ ret = SCX_TEST_PASS;
+out:
+ stop_victim(&challenger);
+ stop_victim(&victim);
+ if (ops_link)
+ bpf_link__destroy(ops_link);
+ if (skel)
+ kick__destroy(skel);
+ return ret;
+}
+
+static bool observation_valid(const struct observation *obs)
+{
+ return obs->slice_before > 0 && !obs->slice_at_resched;
+}
+
+static int active_lazy_mode(void)
+{
+ char buf[128];
+ FILE *file;
+
+ file = fopen("/sys/kernel/debug/sched/preempt", "r");
+ if (!file)
+ return -1;
+ if (!fgets(buf, sizeof(buf), file)) {
+ fclose(file);
+ return -1;
+ }
+ fclose(file);
+
+ if (strstr(buf, "(lazy)"))
+ return 1;
+ if (strstr(buf, "(full)"))
+ return 0;
+ return -1;
+}
+
+static enum scx_test_status setup_immediate(void **ctx)
+{
+ if (!enum_supported("scx_kick_flags", "SCX_KICK_PREEMPT")) {
+ printf("SKIP: SCX_KICK_PREEMPT is not supported\n");
+ return SCX_TEST_SKIP;
+ }
+ return setup_controller(ctx);
+}
+
+static enum scx_test_status setup_lazy(void **ctx)
+{
+ if (!enum_supported("scx_kick_flags", "SCX_KICK_PREEMPT_LAZY")) {
+ printf("SKIP: SCX_KICK_PREEMPT_LAZY is not supported\n");
+ return SCX_TEST_SKIP;
+ }
+ return setup_immediate(ctx);
+}
+
+static enum scx_test_status setup_tick(void **ctx)
+{
+ if (!enum_supported("scx_ops_flags", "SCX_OPS_LAZY_SLICE_EXPIRY")) {
+ printf("SKIP: SCX_OPS_LAZY_SLICE_EXPIRY is not supported\n");
+ return SCX_TEST_SKIP;
+ }
+ return setup_lazy(ctx);
+}
+
+static enum scx_test_status setup_coalesce(void **ctx)
+{
+ if (!enum_supported("scx_enq_flags", "SCX_ENQ_PREEMPT_LAZY")) {
+ printf("SKIP: SCX_ENQ_PREEMPT_LAZY is not supported\n");
+ return SCX_TEST_SKIP;
+ }
+ return setup_lazy(ctx);
+}
+
+static enum scx_test_status setup_invalid(void **ctx)
+{
+ return setup_lazy(ctx);
+}
+
+static enum scx_test_status run_immediate(void *ctx)
+{
+ struct observation obs;
+ enum scx_test_status status;
+
+ status = trace_one(ctx, KICK_IMMEDIATE, 0, -1, &obs);
+ SCX_EQ(status, SCX_TEST_PASS);
+ SCX_ASSERT(observation_valid(&obs));
+ return SCX_TEST_PASS;
+}
+
+static enum scx_test_status run_lazy(void *ctx)
+{
+ struct observation immediate, lazy;
+ enum scx_test_status status;
+ int lazy_mode;
+
+ status = trace_one(ctx, KICK_IMMEDIATE, 0, -1, &immediate);
+ SCX_EQ(status, SCX_TEST_PASS);
+ SCX_ASSERT(observation_valid(&immediate));
+ status = trace_one(ctx, KICK_LAZY, 0, -1, &lazy);
+ SCX_EQ(status, SCX_TEST_PASS);
+ SCX_ASSERT(observation_valid(&lazy));
+
+ lazy_mode = active_lazy_mode();
+ if (lazy_mode > 0)
+ SCX_FAIL_IF(lazy.resched_tif == immediate.resched_tif,
+ "Lazy mode used immediate TIF %d", lazy.resched_tif);
+ else if (!lazy_mode)
+ SCX_EQ(lazy.resched_tif, immediate.resched_tif);
+ else
+ printf("INFO: preemption mode unavailable; lazy TIF was %d, immediate TIF was %d\n",
+ lazy.resched_tif, immediate.resched_tif);
+
+ return SCX_TEST_PASS;
+}
+
+static enum scx_test_status run_coalesce(void *ctx)
+{
+ struct observation immediate, lazy_first, immediate_first;
+ struct observation plain_first, lazy_then_plain;
+ struct observation both, lazy_wait, enq_both;
+ enum scx_test_status status;
+
+ status = trace_one(ctx, KICK_IMMEDIATE, 0, -1, &immediate);
+ SCX_EQ(status, SCX_TEST_PASS);
+ SCX_ASSERT(observation_valid(&immediate));
+ status = trace_one(ctx, KICK_LAZY_THEN_IMMEDIATE, 0, -1,
+ &lazy_first);
+ SCX_EQ(status, SCX_TEST_PASS);
+ SCX_ASSERT(observation_valid(&lazy_first));
+ status = trace_one(ctx, KICK_IMMEDIATE_THEN_LAZY, 0, -1,
+ &immediate_first);
+ SCX_EQ(status, SCX_TEST_PASS);
+ SCX_ASSERT(observation_valid(&immediate_first));
+ SCX_EQ(lazy_first.resched_tif, immediate.resched_tif);
+ SCX_EQ(immediate_first.resched_tif, immediate.resched_tif);
+
+ /*
+ * A plain kick in the same batch doesn't clear the slice by itself.
+ * The lazy preemption must still expire it, and the plain kick must
+ * still reschedule immediately, whichever came first.
+ */
+ status = trace_one(ctx, KICK_PLAIN_THEN_LAZY, 0, -1,
+ &plain_first);
+ SCX_EQ(status, SCX_TEST_PASS);
+ SCX_ASSERT(observation_valid(&plain_first));
+ status = trace_one(ctx, KICK_LAZY_THEN_PLAIN, 0, -1,
+ &lazy_then_plain);
+ SCX_EQ(status, SCX_TEST_PASS);
+ SCX_ASSERT(observation_valid(&lazy_then_plain));
+ SCX_EQ(plain_first.resched_tif, immediate.resched_tif);
+ SCX_EQ(lazy_then_plain.resched_tif, immediate.resched_tif);
+
+ /* Immediate kick and WAIT both take precedence over lazy preemption. */
+ status = trace_one(ctx, KICK_BOTH, 0, -1, &both);
+ SCX_EQ(status, SCX_TEST_PASS);
+ SCX_ASSERT(observation_valid(&both));
+ status = trace_one(ctx, KICK_LAZY_WAIT, 0, -1, &lazy_wait);
+ SCX_EQ(status, SCX_TEST_PASS);
+ SCX_ASSERT(observation_valid(&lazy_wait));
+ SCX_EQ(both.resched_tif, immediate.resched_tif);
+ SCX_EQ(lazy_wait.resched_tif, immediate.resched_tif);
+ SCX_GT(lazy_wait.nr_wait_callbacks, 0);
+
+ /* Immediate enqueue preemption likewise takes precedence over lazy. */
+ status = trace_one(ctx, ENQ_BOTH, 0, -1, &enq_both);
+ SCX_EQ(status, SCX_TEST_PASS);
+ SCX_ASSERT(observation_valid(&enq_both));
+ SCX_EQ(enq_both.resched_tif, immediate.resched_tif);
+ return SCX_TEST_PASS;
+}
+
+/*
+ * A slice running out at the tick reschedules immediately by default and
+ * lazily with SCX_OPS_LAZY_SLICE_EXPIRY, the way fair.c expires a slice.
+ */
+static enum scx_test_status run_tick(void *ctx)
+{
+ struct observation immediate, lazy, force_lazy, force_immediate;
+ enum scx_test_status status;
+ u64 lazy_flag;
+ int lazy_mode;
+ bool found;
+
+ found = __COMPAT_read_enum("scx_ops_flags", "SCX_OPS_LAZY_SLICE_EXPIRY",
+ &lazy_flag);
+ SCX_ASSERT(found);
+ status = trace_one(ctx, TICK_EXPIRY, 0, -1, &immediate);
+ SCX_EQ(status, SCX_TEST_PASS);
+ SCX_ASSERT(observation_valid(&immediate));
+ status = trace_one(ctx, TICK_EXPIRY, lazy_flag, -1, &lazy);
+ SCX_EQ(status, SCX_TEST_PASS);
+ SCX_ASSERT(observation_valid(&lazy));
+ status = trace_one(ctx, TICK_EXPIRY, 0, 1, &force_lazy);
+ SCX_EQ(status, SCX_TEST_PASS);
+ SCX_ASSERT(observation_valid(&force_lazy));
+ status = trace_one(ctx, TICK_EXPIRY, lazy_flag, 0,
+ &force_immediate);
+ SCX_EQ(status, SCX_TEST_PASS);
+ SCX_ASSERT(observation_valid(&force_immediate));
+
+ lazy_mode = active_lazy_mode();
+ if (lazy_mode > 0)
+ SCX_FAIL_IF(lazy.resched_tif == immediate.resched_tif,
+ "Lazy slice expiry used immediate TIF %d", lazy.resched_tif);
+ else if (!lazy_mode)
+ SCX_EQ(lazy.resched_tif, immediate.resched_tif);
+ else
+ printf("INFO: preemption mode unavailable; lazy TIF was %d, immediate TIF was %d\n",
+ lazy.resched_tif, immediate.resched_tif);
+ SCX_EQ(force_lazy.resched_tif, lazy.resched_tif);
+ SCX_EQ(force_immediate.resched_tif, immediate.resched_tif);
+
+ return SCX_TEST_PASS;
+}
+
+static enum scx_test_status invalid_one(struct kick_ctx *ctx, u32 scenario)
+{
+ struct bpf_link *ops_link = NULL;
+ struct kick *skel = NULL;
+ struct victim victim;
+ enum scx_test_status ret = SCX_TEST_FAIL;
+ int cpu = ctx->target_cpu;
+ int i;
+
+ victim = spawn_victim(cpu);
+ if (victim.pid < 0)
+ return SCX_TEST_FAIL;
+
+ skel = kick__open();
+ if (!skel)
+ goto out;
+ SCX_ENUM_INIT(skel);
+ skel->rodata->scenario = scenario;
+ if (kick__load(skel))
+ goto out;
+ ops_link = bpf_map__attach_struct_ops(skel->maps.kick_ops);
+ if (!ops_link || !start_victim(&victim))
+ goto out;
+
+ for (i = 0; i < WAIT_LOOPS; i++) {
+ if (skel->data->uei.kind == EXIT_KIND(SCX_EXIT_ERROR)) {
+ ret = SCX_TEST_PASS;
+ break;
+ }
+ usleep(1000);
+ }
+out:
+ stop_victim(&victim);
+ if (ops_link)
+ bpf_link__destroy(ops_link);
+ if (skel)
+ kick__destroy(skel);
+ return ret;
+}
+
+static enum scx_test_status run_invalid(void *ctx)
+{
+ enum scx_test_status status;
+ u32 scenario;
+
+ for (scenario = INVALID_KICK_IDLE;
+ scenario <= INVALID_KICK_UNKNOWN; scenario++) {
+ status = invalid_one(ctx, scenario);
+ SCX_EQ(status, SCX_TEST_PASS);
+ }
+ return SCX_TEST_PASS;
+}
+
+static struct scx_test kick_immediate = {
+ .name = "kick_immediate",
+ .description = "Trace immediate kick slice expiration and rescheduling",
+ .setup = setup_immediate,
+ .run = run_immediate,
+ .cleanup = cleanup_controller,
+};
+
+static struct scx_test kick_lazy = {
+ .name = "kick_lazy",
+ .description = "Trace lazy kick slice expiration and rescheduling",
+ .setup = setup_lazy,
+ .run = run_lazy,
+ .cleanup = cleanup_controller,
+};
+
+static struct scx_test kick_coalesce = {
+ .name = "kick_coalesce",
+ .description = "Verify lazy preemption coalesces with immediate requests",
+ .setup = setup_coalesce,
+ .run = run_coalesce,
+ .cleanup = cleanup_controller,
+};
+
+static struct scx_test kick_tick = {
+ .name = "kick_tick",
+ .description = "Trace slice expiry at the tick, immediate and lazy",
+ .setup = setup_tick,
+ .run = run_tick,
+ .cleanup = cleanup_controller,
+};
+
+static struct scx_test kick_invalid = {
+ .name = "kick_invalid",
+ .description = "Verify invalid kick flag combinations fail",
+ .setup = setup_invalid,
+ .run = run_invalid,
+ .cleanup = cleanup_controller,
+};
+
+__attribute__((constructor))
+static void register_kick_tests(void)
+{
+ scx_test_register(&kick_immediate);
+ scx_test_register(&kick_lazy);
+ scx_test_register(&kick_coalesce);
+ scx_test_register(&kick_tick);
+ scx_test_register(&kick_invalid);
+}
diff --git a/tools/testing/selftests/sched_ext/nohz_tick.bpf.c b/tools/testing/selftests/sched_ext/nohz_tick.bpf.c
index 6998c5dd6bcb9..96ba1524ca384 100644
--- a/tools/testing/selftests/sched_ext/nohz_tick.bpf.c
+++ b/tools/testing/selftests/sched_ext/nohz_tick.bpf.c
@@ -9,10 +9,23 @@
char _license[] SEC("license") = "GPL";
const volatile s32 test_cpu;
-bool finite_phase;
+enum nohz_phase {
+ NOHZ_PHASE_INF,
+ NOHZ_PHASE_FINITE,
+ NOHZ_PHASE_LAZY_ENQ,
+ NOHZ_PHASE_LAZY_KICK,
+};
+
+u32 phase;
+s32 victim_pid;
+s32 challenger_pid;
+s32 trigger_pid;
u64 nr_inf_running;
u64 nr_finite_running;
u64 nr_finite_ticks;
+u64 nr_lazy_victim_running;
+u64 nr_lazy_enq_running;
+u64 nr_lazy_kick_running;
UEI_DEFINE(uei);
@@ -24,9 +37,31 @@ s32 BPF_STRUCT_OPS(nohz_tick_select_cpu, struct task_struct *p, s32 prev_cpu,
void BPF_STRUCT_OPS(nohz_tick_enqueue, struct task_struct *p, u64 enq_flags)
{
- u64 slice = finite_phase ? 1000000ULL : SCX_SLICE_INF;
+ u64 slice;
+ u64 dsq_id = SCX_DSQ_GLOBAL;
+
+ switch (phase) {
+ case NOHZ_PHASE_INF:
+ slice = SCX_SLICE_INF;
+ break;
+ case NOHZ_PHASE_FINITE:
+ slice = 1000000ULL;
+ break;
+ case NOHZ_PHASE_LAZY_ENQ:
+ case NOHZ_PHASE_LAZY_KICK:
+ dsq_id = SCX_DSQ_LOCAL;
+ slice = p->pid == victim_pid ? SCX_SLICE_INF : SCX_SLICE_DFL;
+ if (phase == NOHZ_PHASE_LAZY_ENQ && p->pid == challenger_pid)
+ enq_flags |= SCX_ENQ_PREEMPT_LAZY;
+ break;
+ default:
+ slice = SCX_SLICE_DFL;
+ break;
+ }
- scx_bpf_dsq_insert(p, SCX_DSQ_GLOBAL, slice, enq_flags);
+ scx_bpf_dsq_insert(p, dsq_id, slice, enq_flags);
+ if (phase == NOHZ_PHASE_LAZY_KICK && p->pid == trigger_pid)
+ scx_bpf_kick_cpu(test_cpu, SCX_KICK_PREEMPT_LAZY);
if (enq_flags & SCX_ENQ_LAST)
scx_bpf_kick_cpu(test_cpu, SCX_KICK_IDLE);
}
@@ -36,15 +71,22 @@ void BPF_STRUCT_OPS(nohz_tick_running, struct task_struct *p)
if (bpf_get_smp_processor_id() != test_cpu)
return;
- if (finite_phase)
+ if (phase == NOHZ_PHASE_FINITE)
__sync_fetch_and_add(&nr_finite_running, 1);
- else
+ else if (phase == NOHZ_PHASE_INF)
__sync_fetch_and_add(&nr_inf_running, 1);
+ else if (p->pid == victim_pid)
+ __sync_fetch_and_add(&nr_lazy_victim_running, 1);
+ else if (phase == NOHZ_PHASE_LAZY_ENQ && p->pid == challenger_pid)
+ __sync_fetch_and_add(&nr_lazy_enq_running, 1);
+ else if (phase == NOHZ_PHASE_LAZY_KICK && p->pid == challenger_pid)
+ __sync_fetch_and_add(&nr_lazy_kick_running, 1);
}
void BPF_STRUCT_OPS(nohz_tick_tick, struct task_struct *p)
{
- if (bpf_get_smp_processor_id() == test_cpu && finite_phase)
+ if (bpf_get_smp_processor_id() == test_cpu &&
+ phase == NOHZ_PHASE_FINITE)
__sync_fetch_and_add(&nr_finite_ticks, 1);
}
@@ -61,5 +103,5 @@ struct sched_ext_ops nohz_tick_ops = {
.tick = (void *)nohz_tick_tick,
.exit = (void *)nohz_tick_exit,
.name = "nohz_tick",
- .timeout_ms = 1000U,
+ .timeout_ms = 5000U,
};
diff --git a/tools/testing/selftests/sched_ext/nohz_tick.c b/tools/testing/selftests/sched_ext/nohz_tick.c
index 028f54391c2ca..acc6510e239ad 100644
--- a/tools/testing/selftests/sched_ext/nohz_tick.c
+++ b/tools/testing/selftests/sched_ext/nohz_tick.c
@@ -28,12 +28,26 @@
#endif
#define MIN_FINITE_TICKS 3
-#define PHASE_TIMEOUT_MS 1000
+#define PHASE_TIMEOUT_MS 5000
struct nohz_tick_ctx {
struct nohz_tick *skel;
cpu_set_t original_mask;
int test_cpu;
+ int housekeeping_cpu;
+ bool lazy_supported;
+};
+
+enum nohz_phase {
+ NOHZ_PHASE_INF,
+ NOHZ_PHASE_FINITE,
+ NOHZ_PHASE_LAZY_ENQ,
+ NOHZ_PHASE_LAZY_KICK,
+};
+
+struct gated_worker {
+ pid_t pid;
+ int start_fd;
};
static int first_allowed_cpu(const cpu_set_t *mask, int first, int last)
@@ -47,20 +61,21 @@ static int first_allowed_cpu(const cpu_set_t *mask, int first, int last)
return -1;
}
-static int find_nohz_full_cpu(const cpu_set_t *allowed)
+static int read_nohz_full_mask(cpu_set_t *mask)
{
char buf[4096], *cur, *end;
FILE *file;
+ int ret = 0;
file = fopen("/sys/devices/system/cpu/nohz_full", "r");
if (!file)
- return -1;
+ return -errno;
if (!fgets(buf, sizeof(buf), file)) {
- fclose(file);
- return -1;
+ ret = ferror(file) ? -errno : -EINVAL;
+ goto out;
}
- fclose(file);
+ CPU_ZERO(mask);
cur = buf;
while (*cur) {
long first, last;
@@ -73,25 +88,30 @@ static int find_nohz_full_cpu(const cpu_set_t *allowed)
errno = 0;
first = strtol(cur, &end, 10);
- if (errno || end == cur || first < 0 || first >= CPU_SETSIZE)
- return -1;
+ if (errno || end == cur || first < 0 || first >= CPU_SETSIZE) {
+ ret = -EINVAL;
+ goto out;
+ }
cur = end;
last = first;
if (*cur == '-') {
cur++;
errno = 0;
last = strtol(cur, &end, 10);
- if (errno || end == cur || last < first)
- return -1;
+ if (errno || end == cur || last < first) {
+ ret = -EINVAL;
+ goto out;
+ }
cur = end;
}
- cpu = first_allowed_cpu(allowed, first, last);
- if (cpu >= 0)
- return cpu;
+ for (cpu = first; cpu <= last && cpu < CPU_SETSIZE; cpu++)
+ CPU_SET(cpu, mask);
}
- return -1;
+out:
+ fclose(file);
+ return ret;
}
static pid_t start_worker(int cpu)
@@ -132,6 +152,87 @@ static void stop_worker(pid_t pid)
waitpid(pid, NULL, 0);
}
+static struct gated_worker spawn_gated_worker(int cpu)
+{
+ struct gated_worker worker = { .pid = -1, .start_fd = -1 };
+ int ready[2], start[2];
+ pid_t parent = getpid();
+ char byte = 1;
+
+ if (pipe(ready))
+ return worker;
+ if (pipe(start)) {
+ close(ready[0]);
+ close(ready[1]);
+ return worker;
+ }
+
+ worker.pid = fork();
+ if (!worker.pid) {
+ struct sched_param param = {};
+ cpu_set_t mask;
+
+ close(ready[0]);
+ close(start[1]);
+ if (prctl(PR_SET_PDEATHSIG, SIGKILL) || getppid() != parent)
+ _exit(1);
+ CPU_ZERO(&mask);
+ CPU_SET(cpu, &mask);
+ if (sched_setaffinity(0, sizeof(mask), &mask))
+ _exit(1);
+ if (sched_setscheduler(0, SCHED_EXT, ¶m))
+ _exit(1);
+ if (write(ready[1], &byte, 1) != 1)
+ _exit(1);
+ close(ready[1]);
+ if (read(start[0], &byte, 1) != 1)
+ _exit(1);
+ close(start[0]);
+ for (;;)
+ asm volatile("" ::: "memory");
+ }
+ if (worker.pid < 0) {
+ close(ready[0]);
+ close(ready[1]);
+ close(start[0]);
+ close(start[1]);
+ return worker;
+ }
+
+ close(ready[1]);
+ close(start[0]);
+ if (read(ready[0], &byte, 1) != 1) {
+ close(ready[0]);
+ close(start[1]);
+ kill(worker.pid, SIGKILL);
+ waitpid(worker.pid, NULL, 0);
+ worker.pid = -1;
+ return worker;
+ }
+ close(ready[0]);
+ worker.start_fd = start[1];
+ return worker;
+}
+
+static bool start_gated_worker(struct gated_worker *worker)
+{
+ char byte = 1;
+
+ if (write(worker->start_fd, &byte, 1) != 1)
+ return false;
+ close(worker->start_fd);
+ worker->start_fd = -1;
+ return true;
+}
+
+static void stop_gated_worker(struct gated_worker *worker)
+{
+ if (worker->start_fd >= 0)
+ close(worker->start_fd);
+ stop_worker(worker->pid);
+ worker->pid = -1;
+}
+
static int pause_worker(pid_t pid)
{
int status;
@@ -162,8 +263,9 @@ static bool wait_for_counter(const u64 *counter, u64 value, int timeout_ms)
static enum scx_test_status setup(void **ctx_ptr)
{
struct nohz_tick_ctx *ctx;
- cpu_set_t controller_mask;
- int cpu;
+ cpu_set_t controller_mask, nohz_full_mask;
+ u64 enum_value;
+ int cpu, i, ret;
ctx = calloc(1, sizeof(*ctx));
SCX_FAIL_IF(!ctx, "Failed to allocate context");
@@ -173,15 +275,27 @@ static enum scx_test_status setup(void **ctx_ptr)
SCX_FAIL("Failed to get affinity (%d)", errno);
}
- cpu = find_nohz_full_cpu(&ctx->original_mask);
- if (cpu < 0) {
+ ret = read_nohz_full_mask(&nohz_full_mask);
+ if (ret) {
+ fprintf(stderr, "SKIP: failed to read NOHZ_FULL mask (%d)\n", ret);
+ free(ctx);
+ return SCX_TEST_SKIP;
+ }
+
+ for (cpu = 0; cpu < CPU_SETSIZE; cpu++)
+ if (CPU_ISSET(cpu, &ctx->original_mask) &&
+ CPU_ISSET(cpu, &nohz_full_mask))
+ break;
+ if (cpu == CPU_SETSIZE) {
fprintf(stderr, "SKIP: no allowed NOHZ_FULL CPU\n");
free(ctx);
return SCX_TEST_SKIP;
}
controller_mask = ctx->original_mask;
- CPU_CLR(cpu, &controller_mask);
+ for (i = 0; i < CPU_SETSIZE; i++)
+ if (CPU_ISSET(i, &nohz_full_mask))
+ CPU_CLR(i, &controller_mask);
if (CPU_COUNT(&controller_mask) == 0) {
fprintf(stderr, "SKIP: no housekeeping CPU available\n");
free(ctx);
@@ -189,6 +303,13 @@ static enum scx_test_status setup(void **ctx_ptr)
}
ctx->test_cpu = cpu;
+ ctx->housekeeping_cpu = first_allowed_cpu(&controller_mask, 0,
+ CPU_SETSIZE - 1);
+ ctx->lazy_supported =
+ __COMPAT_read_enum("scx_enq_flags", "SCX_ENQ_PREEMPT_LAZY",
+ &enum_value) &&
+ __COMPAT_read_enum("scx_kick_flags", "SCX_KICK_PREEMPT_LAZY",
+ &enum_value);
ctx->skel = nohz_tick__open();
if (!ctx->skel) {
free(ctx);
@@ -220,11 +341,15 @@ static enum scx_test_status run(void *ctx_ptr)
struct nohz_tick_ctx *ctx = ctx_ptr;
struct nohz_tick *skel = ctx->skel;
struct bpf_link *link = NULL;
+ struct gated_worker victim = { .pid = -1, .start_fd = -1 };
+ struct gated_worker challenger = { .pid = -1, .start_fd = -1 };
+ struct gated_worker trigger = { .pid = -1, .start_fd = -1 };
enum scx_test_status status = SCX_TEST_FAIL;
pid_t finite_worker = -1;
pid_t inf_worker = -1;
u64 finite_running;
u64 finite_ticks;
+ u64 victim_running;
int ret;
link = bpf_map__attach_struct_ops(skel->maps.nohz_tick_ops);
@@ -260,7 +385,8 @@ static enum scx_test_status run(void *ctx_ptr)
/*
* The next EXT task receives a finite slice and must restart the tick.
*/
- __atomic_store_n(&skel->bss->finite_phase, true, __ATOMIC_RELEASE);
+ __atomic_store_n(&skel->bss->phase, NOHZ_PHASE_FINITE,
+ __ATOMIC_RELEASE);
finite_worker = start_worker(ctx->test_cpu);
if (finite_worker < 0) {
SCX_ERR("Failed to start finite-slice worker (%d)", errno);
@@ -308,7 +434,87 @@ static enum scx_test_status run(void *ctx_ptr)
finite_ticks));
goto out;
}
+ stop_worker(finite_worker);
+ finite_worker = -1;
+ stop_worker(inf_worker);
+ inf_worker = -1;
+ if (!ctx->lazy_supported)
+ goto check_exit;
+
+ /*
+ * A lazy local enqueue must restart the tick after clearing the slice of
+ * an infinite-slice task on a full-dynticks CPU.
+ */
+ __atomic_store_n(&skel->bss->phase, NOHZ_PHASE_LAZY_ENQ,
+ __ATOMIC_RELEASE);
+ victim = spawn_gated_worker(ctx->test_cpu);
+ challenger = spawn_gated_worker(ctx->test_cpu);
+ if (victim.pid < 0 || challenger.pid < 0) {
+ SCX_ERR("Failed to spawn lazy-enqueue workers");
+ goto out;
+ }
+ skel->bss->victim_pid = victim.pid;
+ skel->bss->challenger_pid = challenger.pid;
+ if (!start_gated_worker(&victim) ||
+ !wait_for_counter(&skel->bss->nr_lazy_victim_running, 1,
+ PHASE_TIMEOUT_MS)) {
+ SCX_ERR("Lazy-enqueue victim was not scheduled");
+ goto out;
+ }
+ usleep(100000);
+
+ if (!start_gated_worker(&challenger) ||
+ !wait_for_counter(&skel->bss->nr_lazy_enq_running, 1,
+ PHASE_TIMEOUT_MS)) {
+ SCX_ERR("Lazy enqueue made no progress on CPU %d", ctx->test_cpu);
+ goto out;
+ }
+ stop_gated_worker(&challenger);
+ stop_gated_worker(&victim);
+
+ /* Repeat with a lazy kick delivered from a housekeeping CPU. */
+ __atomic_store_n(&skel->bss->phase, NOHZ_PHASE_LAZY_KICK,
+ __ATOMIC_RELEASE);
+ victim = spawn_gated_worker(ctx->test_cpu);
+ challenger = spawn_gated_worker(ctx->test_cpu);
+ trigger = spawn_gated_worker(ctx->housekeeping_cpu);
+ if (victim.pid < 0 || challenger.pid < 0 || trigger.pid < 0) {
+ SCX_ERR("Failed to spawn lazy-kick workers");
+ goto out;
+ }
+ skel->bss->victim_pid = victim.pid;
+ skel->bss->challenger_pid = challenger.pid;
+ skel->bss->trigger_pid = trigger.pid;
+ victim_running = __atomic_load_n(&skel->bss->nr_lazy_victim_running,
+ __ATOMIC_RELAXED);
+ if (!start_gated_worker(&victim) ||
+ !wait_for_counter(&skel->bss->nr_lazy_victim_running,
+ victim_running + 1,
+ PHASE_TIMEOUT_MS)) {
+ SCX_ERR("Lazy-kick victim was not scheduled");
+ goto out;
+ }
+ if (!start_gated_worker(&challenger)) {
+ SCX_ERR("Failed to start lazy-kick challenger");
+ goto out;
+ }
+ usleep(100000);
+ if (__atomic_load_n(&skel->bss->nr_lazy_kick_running,
+ __ATOMIC_RELAXED)) {
+ SCX_ERR("Lazy-kick challenger ran before the kick");
+ goto out;
+ }
+ if (!start_gated_worker(&trigger) ||
+ !wait_for_counter(&skel->bss->nr_lazy_kick_running, 1,
+ PHASE_TIMEOUT_MS)) {
+ SCX_ERR("Lazy kick made no progress on CPU %d", ctx->test_cpu);
+ goto out;
+ }
+ stop_gated_worker(&trigger);
+ stop_gated_worker(&challenger);
+ stop_gated_worker(&victim);
+check_exit:
if (skel->data->uei.kind != EXIT_KIND(SCX_EXIT_NONE)) {
SCX_ERR("Scheduler exited unexpectedly (kind=%llu code=%lld)",
(unsigned long long)skel->data->uei.kind,
@@ -321,6 +527,9 @@ static enum scx_test_status run(void *ctx_ptr)
(unsigned long long)skel->bss->nr_finite_ticks);
status = SCX_TEST_PASS;
out:
+ stop_gated_worker(&trigger);
+ stop_gated_worker(&challenger);
+ stop_gated_worker(&victim);
stop_worker(finite_worker);
stop_worker(inf_worker);
if (link)
--
2.55.0
^ permalink raw reply [flat|nested] 8+ messages in thread
* [PATCH 2/2] selftests/sched_ext: Add lazy preemption tests
2026-09-14 14:44 [PATCHSET v3 sched_ext/for-7.4] sched_ext: Add lazy preemption support Andrea Righi
@ 2026-09-14 14:44 ` Andrea Righi
0 siblings, 0 replies; 8+ messages in thread
From: Andrea Righi @ 2026-09-14 14:44 UTC (permalink / raw)
To: Tejun Heo, David Vernet, Changwoo Min
Cc: Emil Tsalapatis, sched-ext, linux-kernel
Add trace-based coverage for immediate and lazy preemption. An fexit
probe on __resched_curr() records the requested TIF and the current task
slice, while the stopping callback verifies that the task reaches a
scheduling boundary.
Exercise kick requests individually, in both orders and combined in one
call. Verify that immediate preemption and WAIT take precedence over
lazy preemption, and that combining immediate and lazy enqueue
preemption follows the same rule. Also test overriding the expiry
default in both directions through scx_bpf_task_set_slice_expiry().
Extend the NO_HZ_FULL test with infinite-slice victims. Verify that lazy
enqueue and kick requests restart a stopped tick and make forward
progress. Keep invalid kick flag coverage and skip modes not exposed by
the running kernel.
Signed-off-by: Andrea Righi <arighi@nvidia.com>
---
tools/testing/selftests/sched_ext/Makefile | 1 +
tools/testing/selftests/sched_ext/kick.bpf.c | 166 ++++++
tools/testing/selftests/sched_ext/kick.c | 530 ++++++++++++++++++
.../selftests/sched_ext/nohz_tick.bpf.c | 56 +-
tools/testing/selftests/sched_ext/nohz_tick.c | 195 ++++++-
5 files changed, 939 insertions(+), 9 deletions(-)
create mode 100644 tools/testing/selftests/sched_ext/kick.bpf.c
create mode 100644 tools/testing/selftests/sched_ext/kick.c
diff --git a/tools/testing/selftests/sched_ext/Makefile b/tools/testing/selftests/sched_ext/Makefile
index 5f5dd9ab903ae..c4ec9b21a4c2a 100644
--- a/tools/testing/selftests/sched_ext/Makefile
+++ b/tools/testing/selftests/sched_ext/Makefile
@@ -172,6 +172,7 @@ auto-test-targets := \
exit \
hotplug \
init_enable_count \
+ kick \
maximal \
maybe_null \
minimal \
diff --git a/tools/testing/selftests/sched_ext/kick.bpf.c b/tools/testing/selftests/sched_ext/kick.bpf.c
new file mode 100644
index 0000000000000..03ddc44faf5c4
--- /dev/null
+++ b/tools/testing/selftests/sched_ext/kick.bpf.c
@@ -0,0 +1,166 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (c) 2026 NVIDIA CORPORATION & AFFILIATES
+ */
+#include <scx/common.bpf.h>
+
+char _license[] SEC("license") = "GPL";
+
+enum kick_scenario {
+ KICK_IMMEDIATE,
+ KICK_LAZY,
+ KICK_LAZY_THEN_IMMEDIATE,
+ KICK_IMMEDIATE_THEN_LAZY,
+ KICK_PLAIN_THEN_LAZY,
+ KICK_LAZY_THEN_PLAIN,
+ KICK_BOTH,
+ KICK_LAZY_WAIT,
+ ENQ_BOTH,
+ TICK_EXPIRY,
+ INVALID_KICK_IDLE,
+ INVALID_KICK_UNKNOWN,
+};
+
+enum kick_state {
+ KICK_STATE_IDLE,
+ KICK_STATE_ARMED,
+ KICK_STATE_QUEUED,
+ KICK_STATE_RESCHED,
+ KICK_STATE_DONE,
+};
+
+const volatile u32 scenario;
+const volatile s32 victim_pid;
+const volatile s32 target_cpu;
+const volatile s32 slice_expiry_override = -1;
+
+u32 state;
+u64 slice_before;
+u64 slice_at_resched;
+s32 resched_tif;
+
+UEI_DEFINE(uei);
+
+static bool is_trace_scenario(void)
+{
+ return scenario <= TICK_EXPIRY;
+}
+
+void BPF_STRUCT_OPS(kick_enqueue, struct task_struct *p, u64 enq_flags)
+{
+ switch (scenario) {
+ case ENQ_BOTH:
+ if (p->pid == victim_pid) {
+ scx_bpf_dsq_insert(p, SCX_DSQ_GLOBAL, SCX_SLICE_INF,
+ enq_flags);
+ } else if (state == KICK_STATE_QUEUED) {
+ scx_bpf_dsq_insert(p, SCX_DSQ_LOCAL, SCX_SLICE_DFL,
+ enq_flags | SCX_ENQ_PREEMPT |
+ SCX_ENQ_PREEMPT_LAZY);
+ } else {
+ scx_bpf_dsq_insert(p, SCX_DSQ_GLOBAL, SCX_SLICE_DFL,
+ enq_flags);
+ }
+ return;
+ case INVALID_KICK_IDLE:
+ scx_bpf_kick_cpu(scx_bpf_task_cpu(p), SCX_KICK_PREEMPT_LAZY | SCX_KICK_IDLE);
+ break;
+ case INVALID_KICK_UNKNOWN:
+ scx_bpf_kick_cpu(scx_bpf_task_cpu(p), 1LLU << 63);
+ break;
+ }
+
+ scx_bpf_dsq_insert(p, SCX_DSQ_GLOBAL, SCX_SLICE_DFL, enq_flags);
+}
+
+static void set_slice_expiry_override(struct task_struct *p)
+{
+ if (p->pid == victim_pid && slice_expiry_override >= 0)
+ scx_bpf_task_set_slice_expiry(p, slice_expiry_override);
+}
+
+void BPF_STRUCT_OPS(kick_running, struct task_struct *p)
+{
+ if (!is_trace_scenario() || p->pid != victim_pid)
+ return;
+ set_slice_expiry_override(p);
+ if (__sync_val_compare_and_swap(&state, KICK_STATE_ARMED, KICK_STATE_QUEUED) !=
+ KICK_STATE_ARMED)
+ return;
+
+ slice_before = p->scx.slice;
+
+ switch (scenario) {
+ case KICK_IMMEDIATE:
+ scx_bpf_kick_cpu(target_cpu, SCX_KICK_PREEMPT);
+ break;
+ case KICK_LAZY:
+ scx_bpf_kick_cpu(target_cpu, SCX_KICK_PREEMPT_LAZY);
+ break;
+ case KICK_LAZY_THEN_IMMEDIATE:
+ scx_bpf_kick_cpu(target_cpu, SCX_KICK_PREEMPT_LAZY);
+ scx_bpf_kick_cpu(target_cpu, SCX_KICK_PREEMPT);
+ break;
+ case KICK_IMMEDIATE_THEN_LAZY:
+ scx_bpf_kick_cpu(target_cpu, SCX_KICK_PREEMPT);
+ scx_bpf_kick_cpu(target_cpu, SCX_KICK_PREEMPT_LAZY);
+ break;
+ case KICK_PLAIN_THEN_LAZY:
+ scx_bpf_kick_cpu(target_cpu, 0);
+ scx_bpf_kick_cpu(target_cpu, SCX_KICK_PREEMPT_LAZY);
+ break;
+ case KICK_LAZY_THEN_PLAIN:
+ scx_bpf_kick_cpu(target_cpu, SCX_KICK_PREEMPT_LAZY);
+ scx_bpf_kick_cpu(target_cpu, 0);
+ break;
+ case KICK_BOTH:
+ scx_bpf_kick_cpu(target_cpu, SCX_KICK_PREEMPT |
+ SCX_KICK_PREEMPT_LAZY);
+ break;
+ case KICK_LAZY_WAIT:
+ scx_bpf_kick_cpu(target_cpu, SCX_KICK_PREEMPT_LAZY |
+ SCX_KICK_WAIT);
+ break;
+ case ENQ_BOTH:
+ /* The userspace controller wakes a competing task. */
+ break;
+ case TICK_EXPIRY:
+ /* no kick: the slice runs out at the tick */
+ break;
+ }
+}
+
+SEC("fexit/__resched_curr")
+int BPF_PROG(kick_need_resched, struct rq *rq, int tif)
+{
+ struct task_struct *task = BPF_CORE_READ(rq, curr);
+
+ if (!task || BPF_CORE_READ(task, pid) != victim_pid ||
+ BPF_CORE_READ(rq, cpu) != target_cpu || state != KICK_STATE_QUEUED)
+ return 0;
+
+ slice_at_resched = BPF_CORE_READ(task, scx.slice);
+ resched_tif = tif;
+ state = KICK_STATE_RESCHED;
+ return 0;
+}
+
+void BPF_STRUCT_OPS(kick_stopping, struct task_struct *p, bool runnable)
+{
+ if (p->pid == victim_pid && state == KICK_STATE_RESCHED)
+ state = KICK_STATE_DONE;
+}
+
+void BPF_STRUCT_OPS(kick_exit, struct scx_exit_info *ei)
+{
+ UEI_RECORD(uei, ei);
+}
+
+SEC(".struct_ops.link")
+struct sched_ext_ops kick_ops = {
+ .enqueue = (void *)kick_enqueue,
+ .running = (void *)kick_running,
+ .stopping = (void *)kick_stopping,
+ .exit = (void *)kick_exit,
+ .name = "kick",
+};
diff --git a/tools/testing/selftests/sched_ext/kick.c b/tools/testing/selftests/sched_ext/kick.c
new file mode 100644
index 0000000000000..b7af2683c2728
--- /dev/null
+++ b/tools/testing/selftests/sched_ext/kick.c
@@ -0,0 +1,530 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (c) 2026 NVIDIA CORPORATION & AFFILIATES
+ */
+#define _GNU_SOURCE
+#include <bpf/bpf.h>
+#include <linux/sched.h>
+#include <sched.h>
+#include <signal.h>
+#include <stdio.h>
+#include <string.h>
+#include <sys/prctl.h>
+#include <sys/wait.h>
+#include <unistd.h>
+#include <scx/common.h>
+
+#include "kick.bpf.skel.h"
+#include "scx_test.h"
+
+#define WAIT_LOOPS 3000
+
+enum kick_scenario {
+ KICK_IMMEDIATE,
+ KICK_LAZY,
+ KICK_LAZY_THEN_IMMEDIATE,
+ KICK_IMMEDIATE_THEN_LAZY,
+ KICK_PLAIN_THEN_LAZY,
+ KICK_LAZY_THEN_PLAIN,
+ KICK_BOTH,
+ KICK_LAZY_WAIT,
+ ENQ_BOTH,
+ TICK_EXPIRY,
+ INVALID_KICK_IDLE,
+ INVALID_KICK_UNKNOWN,
+};
+
+enum kick_state {
+ KICK_STATE_IDLE,
+ KICK_STATE_ARMED,
+ KICK_STATE_QUEUED,
+ KICK_STATE_RESCHED,
+ KICK_STATE_DONE,
+};
+
+struct victim {
+ pid_t pid;
+ int start_fd;
+};
+
+struct observation {
+ u64 slice_before;
+ u64 slice_at_resched;
+ s32 resched_tif;
+};
+
+static bool enum_supported(const char *type, const char *name)
+{
+ u64 value;
+
+ return __COMPAT_read_enum(type, name, &value);
+}
+
+static int pick_target_cpu(void)
+{
+ cpu_set_t mask;
+ int cpu;
+
+ if (sched_getaffinity(0, sizeof(mask), &mask))
+ return -1;
+
+ for (cpu = 0; cpu < CPU_SETSIZE; cpu++)
+ if (CPU_ISSET(cpu, &mask))
+ return cpu;
+
+ return -1;
+}
+
+static struct victim spawn_victim(int cpu)
+{
+ struct victim victim = { .pid = -1, .start_fd = -1 };
+ int ready[2], start[2];
+ pid_t parent = getpid();
+ char byte = 1;
+
+ if (pipe(ready))
+ return victim;
+ if (pipe(start)) {
+ close(ready[0]);
+ close(ready[1]);
+ return victim;
+ }
+
+ victim.pid = fork();
+ if (!victim.pid) {
+ cpu_set_t mask;
+
+ close(ready[0]);
+ close(start[1]);
+ if (prctl(PR_SET_PDEATHSIG, SIGKILL) || getppid() != parent)
+ _exit(1);
+ CPU_ZERO(&mask);
+ CPU_SET(cpu, &mask);
+ if (sched_setaffinity(0, sizeof(mask), &mask))
+ _exit(1);
+ if (write(ready[1], &byte, 1) != 1)
+ _exit(1);
+ close(ready[1]);
+ if (read(start[0], &byte, 1) != 1)
+ _exit(1);
+ close(start[0]);
+ for (;;)
+ asm volatile("" ::: "memory");
+ }
+ if (victim.pid < 0) {
+ close(ready[0]);
+ close(ready[1]);
+ close(start[0]);
+ close(start[1]);
+ return victim;
+ }
+
+ close(ready[1]);
+ close(start[0]);
+ if (read(ready[0], &byte, 1) != 1) {
+ close(ready[0]);
+ close(start[1]);
+ kill(victim.pid, SIGKILL);
+ waitpid(victim.pid, NULL, 0);
+ victim.pid = -1;
+ return victim;
+ }
+ close(ready[0]);
+ victim.start_fd = start[1];
+ return victim;
+}
+
+static void stop_victim(struct victim *victim)
+{
+ if (victim->start_fd >= 0)
+ close(victim->start_fd);
+ if (victim->pid > 0) {
+ kill(victim->pid, SIGKILL);
+ waitpid(victim->pid, NULL, 0);
+ }
+}
+
+static bool start_victim(struct victim *victim)
+{
+ char byte = 1;
+
+ if (write(victim->start_fd, &byte, 1) != 1)
+ return false;
+ close(victim->start_fd);
+ victim->start_fd = -1;
+ return true;
+}
+
+static bool wait_for_state(struct kick *skel, u32 wanted)
+{
+ int i;
+
+ for (i = 0; i < WAIT_LOOPS; i++) {
+ if (__atomic_load_n(&skel->bss->state, __ATOMIC_ACQUIRE) == wanted)
+ return true;
+ if (skel->data->uei.kind != EXIT_KIND(SCX_EXIT_NONE))
+ return false;
+ usleep(1000);
+ }
+ return false;
+}
+
+static enum scx_test_status trace_one(u32 scenario, u64 ops_flags,
+ s32 slice_expiry_override,
+ struct observation *obs)
+{
+ struct bpf_link *ops_link = NULL;
+ struct kick *skel = NULL;
+ struct victim challenger = { .pid = -1, .start_fd = -1 };
+ struct victim victim;
+ enum scx_test_status ret = SCX_TEST_FAIL;
+ int cpu = pick_target_cpu();
+
+ if (cpu < 0) {
+ SCX_ERR("No available CPU");
+ return SCX_TEST_FAIL;
+ }
+ victim = spawn_victim(cpu);
+ if (victim.pid < 0) {
+ SCX_ERR("Failed to spawn victim");
+ return SCX_TEST_FAIL;
+ }
+ if (scenario == ENQ_BOTH) {
+ challenger = spawn_victim(cpu);
+ if (challenger.pid < 0) {
+ SCX_ERR("Failed to spawn enqueue challenger");
+ goto out;
+ }
+ }
+
+ skel = kick__open();
+ if (!skel) {
+ SCX_ERR("Failed to open scenario %u", scenario);
+ goto out;
+ }
+ SCX_ENUM_INIT(skel);
+ skel->rodata->scenario = scenario;
+ skel->rodata->victim_pid = victim.pid;
+ skel->rodata->target_cpu = cpu;
+ skel->rodata->slice_expiry_override = slice_expiry_override;
+ skel->struct_ops.kick_ops->flags |= ops_flags;
+ if (kick__load(skel)) {
+ SCX_ERR("Failed to load scenario %u", scenario);
+ goto out;
+ }
+
+ bpf_map__set_autoattach(skel->maps.kick_ops, false);
+ if (kick__attach(skel)) {
+ SCX_ERR("Failed to attach __resched_curr tracer");
+ goto out;
+ }
+ skel->bss->state = KICK_STATE_ARMED;
+ ops_link = bpf_map__attach_struct_ops(skel->maps.kick_ops);
+ if (!ops_link) {
+ SCX_ERR("Failed to attach scenario %u", scenario);
+ goto out;
+ }
+ if (!start_victim(&victim)) {
+ SCX_ERR("Failed to start victim");
+ goto out;
+ }
+ if (scenario == ENQ_BOTH) {
+ if (!wait_for_state(skel, KICK_STATE_QUEUED)) {
+ SCX_ERR("Enqueue scenario did not arm");
+ goto out;
+ }
+ if (!start_victim(&challenger)) {
+ SCX_ERR("Failed to start enqueue challenger");
+ goto out;
+ }
+ }
+ if (!wait_for_state(skel, KICK_STATE_DONE)) {
+ SCX_ERR("Scenario %u stopped in state %u, exit kind %d", scenario, skel->bss->state,
+ skel->data->uei.kind);
+ goto out;
+ }
+
+ obs->slice_before = skel->bss->slice_before;
+ obs->slice_at_resched = skel->bss->slice_at_resched;
+ obs->resched_tif = skel->bss->resched_tif;
+ ret = SCX_TEST_PASS;
+out:
+ stop_victim(&challenger);
+ stop_victim(&victim);
+ if (ops_link)
+ bpf_link__destroy(ops_link);
+ if (skel)
+ kick__destroy(skel);
+ return ret;
+}
+
+static bool observation_valid(const struct observation *obs)
+{
+ return obs->slice_before > 0 && !obs->slice_at_resched;
+}
+
+static int active_lazy_mode(void)
+{
+ char buf[128];
+ FILE *file;
+
+ file = fopen("/sys/kernel/debug/sched/preempt", "r");
+ if (!file)
+ return -1;
+ if (!fgets(buf, sizeof(buf), file)) {
+ fclose(file);
+ return -1;
+ }
+ fclose(file);
+
+ if (strstr(buf, "(lazy)"))
+ return 1;
+ if (strstr(buf, "(full)"))
+ return 0;
+ return -1;
+}
+
+static enum scx_test_status setup_immediate(void **ctx)
+{
+ if (!enum_supported("scx_kick_flags", "SCX_KICK_PREEMPT")) {
+ printf("SKIP: SCX_KICK_PREEMPT is not supported\n");
+ return SCX_TEST_SKIP;
+ }
+ return SCX_TEST_PASS;
+}
+
+static enum scx_test_status setup_lazy(void **ctx)
+{
+ if (!enum_supported("scx_kick_flags", "SCX_KICK_PREEMPT_LAZY")) {
+ printf("SKIP: SCX_KICK_PREEMPT_LAZY is not supported\n");
+ return SCX_TEST_SKIP;
+ }
+ return setup_immediate(ctx);
+}
+
+static enum scx_test_status setup_tick(void **ctx)
+{
+ if (!enum_supported("scx_ops_flags", "SCX_OPS_LAZY_SLICE_EXPIRY")) {
+ printf("SKIP: SCX_OPS_LAZY_SLICE_EXPIRY is not supported\n");
+ return SCX_TEST_SKIP;
+ }
+ return setup_lazy(ctx);
+}
+
+static enum scx_test_status setup_coalesce(void **ctx)
+{
+ if (!enum_supported("scx_enq_flags", "SCX_ENQ_PREEMPT_LAZY")) {
+ printf("SKIP: SCX_ENQ_PREEMPT_LAZY is not supported\n");
+ return SCX_TEST_SKIP;
+ }
+ return setup_lazy(ctx);
+}
+
+static enum scx_test_status setup_invalid(void **ctx)
+{
+ return setup_lazy(ctx);
+}
+
+static enum scx_test_status run_immediate(void *ctx)
+{
+ struct observation obs;
+
+ SCX_EQ(trace_one(KICK_IMMEDIATE, 0, -1, &obs), SCX_TEST_PASS);
+ SCX_ASSERT(observation_valid(&obs));
+ return SCX_TEST_PASS;
+}
+
+static enum scx_test_status run_lazy(void *ctx)
+{
+ struct observation immediate, lazy;
+ int lazy_mode;
+
+ SCX_EQ(trace_one(KICK_IMMEDIATE, 0, -1, &immediate), SCX_TEST_PASS);
+ SCX_EQ(trace_one(KICK_LAZY, 0, -1, &lazy), SCX_TEST_PASS);
+ SCX_ASSERT(observation_valid(&immediate));
+ SCX_ASSERT(observation_valid(&lazy));
+
+ lazy_mode = active_lazy_mode();
+ if (lazy_mode > 0)
+ SCX_FAIL_IF(lazy.resched_tif == immediate.resched_tif,
+ "Lazy mode used immediate TIF %d", lazy.resched_tif);
+ else if (!lazy_mode)
+ SCX_EQ(lazy.resched_tif, immediate.resched_tif);
+ else
+ printf("INFO: preemption mode unavailable; lazy TIF was %d, immediate TIF was %d\n",
+ lazy.resched_tif, immediate.resched_tif);
+
+ return SCX_TEST_PASS;
+}
+
+static enum scx_test_status run_coalesce(void *ctx)
+{
+ struct observation immediate, lazy_first, immediate_first;
+ struct observation plain_first, lazy_then_plain;
+ struct observation both, lazy_wait, enq_both;
+
+ SCX_EQ(trace_one(KICK_IMMEDIATE, 0, -1, &immediate), SCX_TEST_PASS);
+ SCX_EQ(trace_one(KICK_LAZY_THEN_IMMEDIATE, 0, -1, &lazy_first), SCX_TEST_PASS);
+ SCX_EQ(trace_one(KICK_IMMEDIATE_THEN_LAZY, 0, -1, &immediate_first), SCX_TEST_PASS);
+ SCX_ASSERT(observation_valid(&lazy_first));
+ SCX_ASSERT(observation_valid(&immediate_first));
+ SCX_EQ(lazy_first.resched_tif, immediate.resched_tif);
+ SCX_EQ(immediate_first.resched_tif, immediate.resched_tif);
+
+ /*
+ * A plain kick in the same batch doesn't clear the slice by itself.
+ * The lazy preemption must still expire it, and the plain kick must
+ * still reschedule immediately, whichever came first.
+ */
+ SCX_EQ(trace_one(KICK_PLAIN_THEN_LAZY, 0, -1, &plain_first), SCX_TEST_PASS);
+ SCX_EQ(trace_one(KICK_LAZY_THEN_PLAIN, 0, -1, &lazy_then_plain), SCX_TEST_PASS);
+ SCX_ASSERT(observation_valid(&plain_first));
+ SCX_ASSERT(observation_valid(&lazy_then_plain));
+ SCX_EQ(plain_first.resched_tif, immediate.resched_tif);
+ SCX_EQ(lazy_then_plain.resched_tif, immediate.resched_tif);
+
+ /* Immediate kick and WAIT both take precedence over lazy preemption. */
+ SCX_EQ(trace_one(KICK_BOTH, 0, -1, &both), SCX_TEST_PASS);
+ SCX_EQ(trace_one(KICK_LAZY_WAIT, 0, -1, &lazy_wait), SCX_TEST_PASS);
+ SCX_ASSERT(observation_valid(&both));
+ SCX_ASSERT(observation_valid(&lazy_wait));
+ SCX_EQ(both.resched_tif, immediate.resched_tif);
+ SCX_EQ(lazy_wait.resched_tif, immediate.resched_tif);
+
+ /* Immediate enqueue preemption likewise takes precedence over lazy. */
+ SCX_EQ(trace_one(ENQ_BOTH, 0, -1, &enq_both), SCX_TEST_PASS);
+ SCX_ASSERT(observation_valid(&enq_both));
+ SCX_EQ(enq_both.resched_tif, immediate.resched_tif);
+ return SCX_TEST_PASS;
+}
+
+/*
+ * A slice running out at the tick reschedules immediately by default and
+ * lazily with SCX_OPS_LAZY_SLICE_EXPIRY, the way fair.c expires a slice.
+ */
+static enum scx_test_status run_tick(void *ctx)
+{
+ struct observation immediate, lazy, force_lazy, force_immediate;
+ u64 lazy_flag;
+ int lazy_mode;
+
+ SCX_ASSERT(__COMPAT_read_enum("scx_ops_flags", "SCX_OPS_LAZY_SLICE_EXPIRY", &lazy_flag));
+ SCX_EQ(trace_one(TICK_EXPIRY, 0, -1, &immediate), SCX_TEST_PASS);
+ SCX_EQ(trace_one(TICK_EXPIRY, lazy_flag, -1, &lazy), SCX_TEST_PASS);
+ SCX_EQ(trace_one(TICK_EXPIRY, 0, 1, &force_lazy), SCX_TEST_PASS);
+ SCX_EQ(trace_one(TICK_EXPIRY, lazy_flag, 0, &force_immediate), SCX_TEST_PASS);
+ SCX_ASSERT(observation_valid(&immediate));
+ SCX_ASSERT(observation_valid(&lazy));
+ SCX_ASSERT(observation_valid(&force_lazy));
+ SCX_ASSERT(observation_valid(&force_immediate));
+
+ lazy_mode = active_lazy_mode();
+ if (lazy_mode > 0)
+ SCX_FAIL_IF(lazy.resched_tif == immediate.resched_tif,
+ "Lazy slice expiry used immediate TIF %d", lazy.resched_tif);
+ else if (!lazy_mode)
+ SCX_EQ(lazy.resched_tif, immediate.resched_tif);
+ else
+ printf("INFO: preemption mode unavailable; lazy TIF was %d, immediate TIF was %d\n",
+ lazy.resched_tif, immediate.resched_tif);
+ SCX_EQ(force_lazy.resched_tif, lazy.resched_tif);
+ SCX_EQ(force_immediate.resched_tif, immediate.resched_tif);
+
+ return SCX_TEST_PASS;
+}
+
+static enum scx_test_status invalid_one(u32 scenario)
+{
+ struct bpf_link *ops_link = NULL;
+ struct kick *skel = NULL;
+ struct victim victim;
+ enum scx_test_status ret = SCX_TEST_FAIL;
+ int cpu = pick_target_cpu();
+ int i;
+
+ if (cpu < 0)
+ return SCX_TEST_FAIL;
+ victim = spawn_victim(cpu);
+ if (victim.pid < 0)
+ return SCX_TEST_FAIL;
+
+ skel = kick__open();
+ if (!skel)
+ goto out;
+ SCX_ENUM_INIT(skel);
+ skel->rodata->scenario = scenario;
+ if (kick__load(skel))
+ goto out;
+ ops_link = bpf_map__attach_struct_ops(skel->maps.kick_ops);
+ if (!ops_link || !start_victim(&victim))
+ goto out;
+
+ for (i = 0; i < WAIT_LOOPS; i++) {
+ if (skel->data->uei.kind == EXIT_KIND(SCX_EXIT_ERROR)) {
+ ret = SCX_TEST_PASS;
+ break;
+ }
+ usleep(1000);
+ }
+out:
+ stop_victim(&victim);
+ if (ops_link)
+ bpf_link__destroy(ops_link);
+ if (skel)
+ kick__destroy(skel);
+ return ret;
+}
+
+static enum scx_test_status run_invalid(void *ctx)
+{
+ u32 scenario;
+
+ for (scenario = INVALID_KICK_IDLE; scenario <= INVALID_KICK_UNKNOWN; scenario++)
+ SCX_EQ(invalid_one(scenario), SCX_TEST_PASS);
+ return SCX_TEST_PASS;
+}
+
+static struct scx_test kick_immediate = {
+ .name = "kick_immediate",
+ .description = "Trace immediate kick slice expiration and rescheduling",
+ .setup = setup_immediate,
+ .run = run_immediate,
+};
+
+static struct scx_test kick_lazy = {
+ .name = "kick_lazy",
+ .description = "Trace lazy kick slice expiration and rescheduling",
+ .setup = setup_lazy,
+ .run = run_lazy,
+};
+
+static struct scx_test kick_coalesce = {
+ .name = "kick_coalesce",
+ .description = "Verify lazy preemption coalesces with immediate requests",
+ .setup = setup_coalesce,
+ .run = run_coalesce,
+};
+
+static struct scx_test kick_tick = {
+ .name = "kick_tick",
+ .description = "Trace slice expiry at the tick, immediate and lazy",
+ .setup = setup_tick,
+ .run = run_tick,
+};
+
+static struct scx_test kick_invalid = {
+ .name = "kick_invalid",
+ .description = "Verify invalid kick flag combinations fail",
+ .setup = setup_invalid,
+ .run = run_invalid,
+};
+
+__attribute__((constructor))
+static void register_kick_tests(void)
+{
+ scx_test_register(&kick_immediate);
+ scx_test_register(&kick_lazy);
+ scx_test_register(&kick_coalesce);
+ scx_test_register(&kick_tick);
+ scx_test_register(&kick_invalid);
+}
diff --git a/tools/testing/selftests/sched_ext/nohz_tick.bpf.c b/tools/testing/selftests/sched_ext/nohz_tick.bpf.c
index 6998c5dd6bcb9..96ba1524ca384 100644
--- a/tools/testing/selftests/sched_ext/nohz_tick.bpf.c
+++ b/tools/testing/selftests/sched_ext/nohz_tick.bpf.c
@@ -9,10 +9,23 @@
char _license[] SEC("license") = "GPL";
const volatile s32 test_cpu;
-bool finite_phase;
+enum nohz_phase {
+ NOHZ_PHASE_INF,
+ NOHZ_PHASE_FINITE,
+ NOHZ_PHASE_LAZY_ENQ,
+ NOHZ_PHASE_LAZY_KICK,
+};
+
+u32 phase;
+s32 victim_pid;
+s32 challenger_pid;
+s32 trigger_pid;
u64 nr_inf_running;
u64 nr_finite_running;
u64 nr_finite_ticks;
+u64 nr_lazy_victim_running;
+u64 nr_lazy_enq_running;
+u64 nr_lazy_kick_running;
UEI_DEFINE(uei);
@@ -24,9 +37,31 @@ s32 BPF_STRUCT_OPS(nohz_tick_select_cpu, struct task_struct *p, s32 prev_cpu,
void BPF_STRUCT_OPS(nohz_tick_enqueue, struct task_struct *p, u64 enq_flags)
{
- u64 slice = finite_phase ? 1000000ULL : SCX_SLICE_INF;
+ u64 slice;
+ u64 dsq_id = SCX_DSQ_GLOBAL;
+
+ switch (phase) {
+ case NOHZ_PHASE_INF:
+ slice = SCX_SLICE_INF;
+ break;
+ case NOHZ_PHASE_FINITE:
+ slice = 1000000ULL;
+ break;
+ case NOHZ_PHASE_LAZY_ENQ:
+ case NOHZ_PHASE_LAZY_KICK:
+ dsq_id = SCX_DSQ_LOCAL;
+ slice = p->pid == victim_pid ? SCX_SLICE_INF : SCX_SLICE_DFL;
+ if (phase == NOHZ_PHASE_LAZY_ENQ && p->pid == challenger_pid)
+ enq_flags |= SCX_ENQ_PREEMPT_LAZY;
+ break;
+ default:
+ slice = SCX_SLICE_DFL;
+ break;
+ }
- scx_bpf_dsq_insert(p, SCX_DSQ_GLOBAL, slice, enq_flags);
+ scx_bpf_dsq_insert(p, dsq_id, slice, enq_flags);
+ if (phase == NOHZ_PHASE_LAZY_KICK && p->pid == trigger_pid)
+ scx_bpf_kick_cpu(test_cpu, SCX_KICK_PREEMPT_LAZY);
if (enq_flags & SCX_ENQ_LAST)
scx_bpf_kick_cpu(test_cpu, SCX_KICK_IDLE);
}
@@ -36,15 +71,22 @@ void BPF_STRUCT_OPS(nohz_tick_running, struct task_struct *p)
if (bpf_get_smp_processor_id() != test_cpu)
return;
- if (finite_phase)
+ if (phase == NOHZ_PHASE_FINITE)
__sync_fetch_and_add(&nr_finite_running, 1);
- else
+ else if (phase == NOHZ_PHASE_INF)
__sync_fetch_and_add(&nr_inf_running, 1);
+ else if (p->pid == victim_pid)
+ __sync_fetch_and_add(&nr_lazy_victim_running, 1);
+ else if (phase == NOHZ_PHASE_LAZY_ENQ && p->pid == challenger_pid)
+ __sync_fetch_and_add(&nr_lazy_enq_running, 1);
+ else if (phase == NOHZ_PHASE_LAZY_KICK && p->pid == challenger_pid)
+ __sync_fetch_and_add(&nr_lazy_kick_running, 1);
}
void BPF_STRUCT_OPS(nohz_tick_tick, struct task_struct *p)
{
- if (bpf_get_smp_processor_id() == test_cpu && finite_phase)
+ if (bpf_get_smp_processor_id() == test_cpu &&
+ phase == NOHZ_PHASE_FINITE)
__sync_fetch_and_add(&nr_finite_ticks, 1);
}
@@ -61,5 +103,5 @@ struct sched_ext_ops nohz_tick_ops = {
.tick = (void *)nohz_tick_tick,
.exit = (void *)nohz_tick_exit,
.name = "nohz_tick",
- .timeout_ms = 1000U,
+ .timeout_ms = 5000U,
};
diff --git a/tools/testing/selftests/sched_ext/nohz_tick.c b/tools/testing/selftests/sched_ext/nohz_tick.c
index 028f54391c2ca..6fd74fd629b85 100644
--- a/tools/testing/selftests/sched_ext/nohz_tick.c
+++ b/tools/testing/selftests/sched_ext/nohz_tick.c
@@ -28,12 +28,26 @@
#endif
#define MIN_FINITE_TICKS 3
-#define PHASE_TIMEOUT_MS 1000
+#define PHASE_TIMEOUT_MS 5000
struct nohz_tick_ctx {
struct nohz_tick *skel;
cpu_set_t original_mask;
int test_cpu;
+ int housekeeping_cpu;
+ bool lazy_supported;
+};
+
+enum nohz_phase {
+ NOHZ_PHASE_INF,
+ NOHZ_PHASE_FINITE,
+ NOHZ_PHASE_LAZY_ENQ,
+ NOHZ_PHASE_LAZY_KICK,
+};
+
+struct gated_worker {
+ pid_t pid;
+ int start_fd;
};
static int first_allowed_cpu(const cpu_set_t *mask, int first, int last)
@@ -132,6 +146,87 @@ static void stop_worker(pid_t pid)
waitpid(pid, NULL, 0);
}
+static struct gated_worker spawn_gated_worker(int cpu)
+{
+ struct gated_worker worker = { .pid = -1, .start_fd = -1 };
+ int ready[2], start[2];
+ pid_t parent = getpid();
+ char byte = 1;
+
+ if (pipe(ready))
+ return worker;
+ if (pipe(start)) {
+ close(ready[0]);
+ close(ready[1]);
+ return worker;
+ }
+
+ worker.pid = fork();
+ if (!worker.pid) {
+ struct sched_param param = {};
+ cpu_set_t mask;
+
+ close(ready[0]);
+ close(start[1]);
+ if (prctl(PR_SET_PDEATHSIG, SIGKILL) || getppid() != parent)
+ _exit(1);
+ CPU_ZERO(&mask);
+ CPU_SET(cpu, &mask);
+ if (sched_setaffinity(0, sizeof(mask), &mask))
+ _exit(1);
+ if (sched_setscheduler(0, SCHED_EXT, ¶m))
+ _exit(1);
+ if (write(ready[1], &byte, 1) != 1)
+ _exit(1);
+ close(ready[1]);
+ if (read(start[0], &byte, 1) != 1)
+ _exit(1);
+ close(start[0]);
+ for (;;)
+ asm volatile("" ::: "memory");
+ }
+ if (worker.pid < 0) {
+ close(ready[0]);
+ close(ready[1]);
+ close(start[0]);
+ close(start[1]);
+ return worker;
+ }
+
+ close(ready[1]);
+ close(start[0]);
+ if (read(ready[0], &byte, 1) != 1) {
+ close(ready[0]);
+ close(start[1]);
+ kill(worker.pid, SIGKILL);
+ waitpid(worker.pid, NULL, 0);
+ worker.pid = -1;
+ return worker;
+ }
+ close(ready[0]);
+ worker.start_fd = start[1];
+ return worker;
+}
+
+static bool start_gated_worker(struct gated_worker *worker)
+{
+ char byte = 1;
+
+ if (write(worker->start_fd, &byte, 1) != 1)
+ return false;
+ close(worker->start_fd);
+ worker->start_fd = -1;
+ return true;
+}
+
+static void stop_gated_worker(struct gated_worker *worker)
+{
+ if (worker->start_fd >= 0)
+ close(worker->start_fd);
+ stop_worker(worker->pid);
+ worker->pid = -1;
+}
+
static int pause_worker(pid_t pid)
{
int status;
@@ -163,6 +258,7 @@ static enum scx_test_status setup(void **ctx_ptr)
{
struct nohz_tick_ctx *ctx;
cpu_set_t controller_mask;
+ u64 enum_value;
int cpu;
ctx = calloc(1, sizeof(*ctx));
@@ -189,6 +285,13 @@ static enum scx_test_status setup(void **ctx_ptr)
}
ctx->test_cpu = cpu;
+ ctx->housekeeping_cpu = first_allowed_cpu(&controller_mask, 0,
+ CPU_SETSIZE - 1);
+ ctx->lazy_supported =
+ __COMPAT_read_enum("scx_enq_flags", "SCX_ENQ_PREEMPT_LAZY",
+ &enum_value) &&
+ __COMPAT_read_enum("scx_kick_flags", "SCX_KICK_PREEMPT_LAZY",
+ &enum_value);
ctx->skel = nohz_tick__open();
if (!ctx->skel) {
free(ctx);
@@ -220,11 +323,15 @@ static enum scx_test_status run(void *ctx_ptr)
struct nohz_tick_ctx *ctx = ctx_ptr;
struct nohz_tick *skel = ctx->skel;
struct bpf_link *link = NULL;
+ struct gated_worker victim = { .pid = -1, .start_fd = -1 };
+ struct gated_worker challenger = { .pid = -1, .start_fd = -1 };
+ struct gated_worker trigger = { .pid = -1, .start_fd = -1 };
enum scx_test_status status = SCX_TEST_FAIL;
pid_t finite_worker = -1;
pid_t inf_worker = -1;
u64 finite_running;
u64 finite_ticks;
+ u64 victim_running;
int ret;
link = bpf_map__attach_struct_ops(skel->maps.nohz_tick_ops);
@@ -260,7 +367,8 @@ static enum scx_test_status run(void *ctx_ptr)
/*
* The next EXT task receives a finite slice and must restart the tick.
*/
- __atomic_store_n(&skel->bss->finite_phase, true, __ATOMIC_RELEASE);
+ __atomic_store_n(&skel->bss->phase, NOHZ_PHASE_FINITE,
+ __ATOMIC_RELEASE);
finite_worker = start_worker(ctx->test_cpu);
if (finite_worker < 0) {
SCX_ERR("Failed to start finite-slice worker (%d)", errno);
@@ -308,7 +416,87 @@ static enum scx_test_status run(void *ctx_ptr)
finite_ticks));
goto out;
}
+ stop_worker(finite_worker);
+ finite_worker = -1;
+ stop_worker(inf_worker);
+ inf_worker = -1;
+ if (!ctx->lazy_supported)
+ goto check_exit;
+
+ /*
+ * A lazy local enqueue must restart the tick after clearing the slice of
+ * an infinite-slice task on a full-dynticks CPU.
+ */
+ __atomic_store_n(&skel->bss->phase, NOHZ_PHASE_LAZY_ENQ,
+ __ATOMIC_RELEASE);
+ victim = spawn_gated_worker(ctx->test_cpu);
+ challenger = spawn_gated_worker(ctx->test_cpu);
+ if (victim.pid < 0 || challenger.pid < 0) {
+ SCX_ERR("Failed to spawn lazy-enqueue workers");
+ goto out;
+ }
+ skel->bss->victim_pid = victim.pid;
+ skel->bss->challenger_pid = challenger.pid;
+ if (!start_gated_worker(&victim) ||
+ !wait_for_counter(&skel->bss->nr_lazy_victim_running, 1,
+ PHASE_TIMEOUT_MS)) {
+ SCX_ERR("Lazy-enqueue victim was not scheduled");
+ goto out;
+ }
+ usleep(100000);
+
+ if (!start_gated_worker(&challenger) ||
+ !wait_for_counter(&skel->bss->nr_lazy_enq_running, 1,
+ PHASE_TIMEOUT_MS)) {
+ SCX_ERR("Lazy enqueue made no progress on CPU %d", ctx->test_cpu);
+ goto out;
+ }
+ stop_gated_worker(&challenger);
+ stop_gated_worker(&victim);
+
+ /* Repeat with a lazy kick delivered from a housekeeping CPU. */
+ __atomic_store_n(&skel->bss->phase, NOHZ_PHASE_LAZY_KICK,
+ __ATOMIC_RELEASE);
+ victim = spawn_gated_worker(ctx->test_cpu);
+ challenger = spawn_gated_worker(ctx->test_cpu);
+ trigger = spawn_gated_worker(ctx->housekeeping_cpu);
+ if (victim.pid < 0 || challenger.pid < 0 || trigger.pid < 0) {
+ SCX_ERR("Failed to spawn lazy-kick workers");
+ goto out;
+ }
+ skel->bss->victim_pid = victim.pid;
+ skel->bss->challenger_pid = challenger.pid;
+ skel->bss->trigger_pid = trigger.pid;
+ victim_running = __atomic_load_n(&skel->bss->nr_lazy_victim_running,
+ __ATOMIC_RELAXED);
+ if (!start_gated_worker(&victim) ||
+ !wait_for_counter(&skel->bss->nr_lazy_victim_running,
+ victim_running + 1,
+ PHASE_TIMEOUT_MS)) {
+ SCX_ERR("Lazy-kick victim was not scheduled");
+ goto out;
+ }
+ if (!start_gated_worker(&challenger)) {
+ SCX_ERR("Failed to start lazy-kick challenger");
+ goto out;
+ }
+ usleep(100000);
+ if (__atomic_load_n(&skel->bss->nr_lazy_kick_running,
+ __ATOMIC_RELAXED)) {
+ SCX_ERR("Lazy-kick challenger ran before the kick");
+ goto out;
+ }
+ if (!start_gated_worker(&trigger) ||
+ !wait_for_counter(&skel->bss->nr_lazy_kick_running, 1,
+ PHASE_TIMEOUT_MS)) {
+ SCX_ERR("Lazy kick made no progress on CPU %d", ctx->test_cpu);
+ goto out;
+ }
+ stop_gated_worker(&trigger);
+ stop_gated_worker(&challenger);
+ stop_gated_worker(&victim);
+check_exit:
if (skel->data->uei.kind != EXIT_KIND(SCX_EXIT_NONE)) {
SCX_ERR("Scheduler exited unexpectedly (kind=%llu code=%lld)",
(unsigned long long)skel->data->uei.kind,
@@ -321,6 +509,9 @@ static enum scx_test_status run(void *ctx_ptr)
(unsigned long long)skel->bss->nr_finite_ticks);
status = SCX_TEST_PASS;
out:
+ stop_gated_worker(&trigger);
+ stop_gated_worker(&challenger);
+ stop_gated_worker(&victim);
stop_worker(finite_worker);
stop_worker(inf_worker);
if (link)
--
2.55.0
^ permalink raw reply [flat|nested] 8+ messages in thread
end of thread, other threads:[~2026-09-15 19:46 UTC | newest]
Thread overview: 8+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2026-09-14 8:47 [PATCHSET v2 sched_ext/for-7.4] sched_ext: Add lazy preemption support Andrea Righi
2026-09-14 8:47 ` [PATCH 1/2] " Andrea Righi
2026-09-14 8:47 ` [PATCH 2/2] selftests/sched_ext: Add lazy preemption tests Andrea Righi
2026-09-14 14:55 ` Cheng-Yang Chou
2026-09-15 13:35 ` Andrea Righi
2026-09-14 14:44 [PATCHSET v3 sched_ext/for-7.4] sched_ext: Add lazy preemption support Andrea Righi
2026-09-14 14:44 ` [PATCH 2/2] selftests/sched_ext: Add lazy preemption tests Andrea Righi
2026-09-15 9:00 [PATCHSET v4 sched_ext/for-7.4] sched_ext: Add lazy preemption support Andrea Righi
2026-09-15 9:00 ` [PATCH 2/2] selftests/sched_ext: Add lazy preemption tests Andrea Righi
2026-09-15 19:45 [PATCHSET v5 sched_ext/for-7.4] sched_ext: Add lazy preemption support Andrea Righi
2026-09-15 19:45 ` [PATCH 2/2] selftests/sched_ext: Add lazy preemption tests Andrea Righi
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