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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 selftests 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 kick: PASSED: 6 SKIPPED: 0 FAILED: 0 $ vng -a "preempt=lazy nohz_full=8-15" -- tools/testing/selftests/sched_ext/runner -t nohz_tick nohz_tick: CPU 8 received 7 finite-slice ticks PASSED: 1 SKIPPED: 0 FAILED: 0 Changes in v4: - Preserve SCX_KICK_WAIT synchronization when it is combined with SCX_KICK_PREEMPT_LAZY (Sashiko). - Restore the scheduler tick dependency when ops.tick() lazily expires an infinite slice, ensuring the request is promoted by a later tick (Sashiko). - kselftest: verify that the deferred SCX_KICK_WAIT callback runs (Sashiko). - kselftest: keep the kick test controller off the victim CPU and skip cleanly when a second allowed CPU is unavailable (Sashiko). - kselftest: select the nohz_tick controller from allowed housekeeping CPUs outside the NOHZ_FULL mask and skip when the required topology is unavailable. - Link to v3: https://lore.kernel.org/r/20260914144620.2032614-1-arighi@nvidia.com Changes in v3: - Avoid redundant rq clock updates when restoring the tick dependency and use the pinned rq lock helpers for lazy kick delivery (Sashiko). - Set PR_SET_PDEATHSIG for the indefinitely spinning kick test workers so they don't survive unexpected test-runner exit (Sashiko). - Wait for a delta in nr_lazy_victim_running instead of an absolute count that may include reschedules from the previous phase (Sashiko). - Increase the nohz_tick scheduler watchdog and phase timeouts to tolerate scheduling delays in oversubscribed test VMs. - Link to v2: https://lore.kernel.org/r/20260914084955.1798562-1-arighi@nvidia.com 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 | 153 +++++- 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 | 182 +++++++ tools/testing/selftests/sched_ext/kick.c | 608 ++++++++++++++++++++++ tools/testing/selftests/sched_ext/nohz_tick.bpf.c | 56 +- tools/testing/selftests/sched_ext/nohz_tick.c | 249 ++++++++- 14 files changed, 1273 insertions(+), 67 deletions(-) create mode 100644 tools/testing/selftests/sched_ext/kick.bpf.c create mode 100644 tools/testing/selftests/sched_ext/kick.c