[RFC][PATCH] sched/ext: Split curr|donor references properly

[John Stultz <jstultz@google.com>]

With proxy-exec, we want to do the accounting against the donor
most of the time. Without proxy-exec, there should be no
difference as the rq->donor and rq->curr are the same.

So rework the logic to reference the rq->donor where appropriate.

Also add donor info to scx_dump_state()

Since CONFIG_SCHED_PROXY_EXEC currently depends on
!CONFIG_SCHED_CLASS_EXT, this should have no effect
(other then the extra donor output in scx_dump_state),
but this is one step needed to eventually remove that
constraint for proxy-exec.

Just wanted to send this out for early review prior to LPC.

Feedback or thoughts would be greatly appreciated!

Signed-off-by: John Stultz <jstultz@google.com>
---
Cc: Joel Fernandes <joelaf@google.com>
Cc: Qais Yousef <qyousef@layalina.io>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Vincent Guittot <vincent.guittot@linaro.org>
Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc: Valentin Schneider <vschneid@redhat.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Ben Segall <bsegall@google.com>
Cc: Zimuzo Ezeozue <zezeozue@google.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Will Deacon <will@kernel.org>
Cc: Waiman Long <longman@redhat.com>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: "Paul E. McKenney" <paulmck@kernel.org>
Cc: Metin Kaya <Metin.Kaya@arm.com>
Cc: Xuewen Yan <xuewen.yan94@gmail.com>
Cc: K Prateek Nayak <kprateek.nayak@amd.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Daniel Lezcano <daniel.lezcano@linaro.org>
Cc: Tejun Heo <tj@kernel.org>
Cc: David Vernet <void@manifault.com>
Cc: Andrea Righi <arighi@nvidia.com>
Cc: Changwoo Min <changwoo@igalia.com>
Cc: sched-ext@lists.linux.dev
Cc: kernel-team@android.com
---
 kernel/sched/ext.c | 31 +++++++++++++++++--------------
 1 file changed, 17 insertions(+), 14 deletions(-)

diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c
index 05f5a49e9649a..446091cba4429 100644
--- a/kernel/sched/ext.c
+++ b/kernel/sched/ext.c
@@ -938,17 +938,17 @@ static void touch_core_sched_dispatch(struct rq *rq, struct task_struct *p)
 
 static void update_curr_scx(struct rq *rq)
 {
-	struct task_struct *curr = rq->curr;
+	struct task_struct *donor = rq->donor;
 	s64 delta_exec;
 
 	delta_exec = update_curr_common(rq);
 	if (unlikely(delta_exec <= 0))
 		return;
 
-	if (curr->scx.slice != SCX_SLICE_INF) {
-		curr->scx.slice -= min_t(u64, curr->scx.slice, delta_exec);
-		if (!curr->scx.slice)
-			touch_core_sched(rq, curr);
+	if (donor->scx.slice != SCX_SLICE_INF) {
+		donor->scx.slice -= min_t(u64, donor->scx.slice, delta_exec);
+		if (!donor->scx.slice)
+			touch_core_sched(rq, donor);
 	}
 }
 
@@ -1090,14 +1090,14 @@ static void dispatch_enqueue(struct scx_sched *sch, struct scx_dispatch_q *dsq,
 		struct rq *rq = container_of(dsq, struct rq, scx.local_dsq);
 		bool preempt = false;
 
-		if ((enq_flags & SCX_ENQ_PREEMPT) && p != rq->curr &&
-		    rq->curr->sched_class == &ext_sched_class) {
-			rq->curr->scx.slice = 0;
+		if ((enq_flags & SCX_ENQ_PREEMPT) && p != rq->donor &&
+		    rq->donor->sched_class == &ext_sched_class) {
+			rq->donor->scx.slice = 0;
 			preempt = true;
 		}
 
 		if (preempt || sched_class_above(&ext_sched_class,
-						 rq->curr->sched_class))
+						 rq->donor->sched_class))
 			resched_curr(rq);
 	} else {
 		raw_spin_unlock(&dsq->lock);
@@ -2001,7 +2001,7 @@ static void dispatch_to_local_dsq(struct scx_sched *sch, struct rq *rq,
 		}
 
 		/* if the destination CPU is idle, wake it up */
-		if (sched_class_above(p->sched_class, dst_rq->curr->sched_class))
+		if (sched_class_above(p->sched_class, dst_rq->donor->sched_class))
 			resched_curr(dst_rq);
 	}
 
@@ -2424,7 +2424,7 @@ static struct task_struct *first_local_task(struct rq *rq)
 static struct task_struct *
 do_pick_task_scx(struct rq *rq, struct rq_flags *rf, bool force_scx)
 {
-	struct task_struct *prev = rq->curr;
+	struct task_struct *prev = rq->donor;
 	bool keep_prev, kick_idle = false;
 	struct task_struct *p;
 
@@ -3093,7 +3093,7 @@ int scx_check_setscheduler(struct task_struct *p, int policy)
 #ifdef CONFIG_NO_HZ_FULL
 bool scx_can_stop_tick(struct rq *rq)
 {
-	struct task_struct *p = rq->curr;
+	struct task_struct *p = rq->donor;
 
 	if (scx_rq_bypassing(rq))
 		return false;
@@ -4587,6 +4587,9 @@ static void scx_dump_state(struct scx_exit_info *ei, size_t dump_len)
 		dump_line(&ns, "          curr=%s[%d] class=%ps",
 			  rq->curr->comm, rq->curr->pid,
 			  rq->curr->sched_class);
+		dump_line(&ns, "          donor=%s[%d] class=%ps",
+			  rq->donor->comm, rq->donor->pid,
+			  rq->donor->sched_class);
 		if (!cpumask_empty(rq->scx.cpus_to_kick))
 			dump_line(&ns, "  cpus_to_kick   : %*pb",
 				  cpumask_pr_args(rq->scx.cpus_to_kick));
@@ -5426,7 +5429,7 @@ static bool kick_one_cpu(s32 cpu, struct rq *this_rq, unsigned long *ksyncs)
 	unsigned long flags;
 
 	raw_spin_rq_lock_irqsave(rq, flags);
-	cur_class = rq->curr->sched_class;
+	cur_class = rq->donor->sched_class;
 
 	/*
 	 * During CPU hotplug, a CPU may depend on kicking itself to make
@@ -5438,7 +5441,7 @@ static bool kick_one_cpu(s32 cpu, struct rq *this_rq, unsigned long *ksyncs)
 	    !sched_class_above(cur_class, &ext_sched_class)) {
 		if (cpumask_test_cpu(cpu, this_scx->cpus_to_preempt)) {
 			if (cur_class == &ext_sched_class)
-				rq->curr->scx.slice = 0;
+				rq->donor->scx.slice = 0;
 			cpumask_clear_cpu(cpu, this_scx->cpus_to_preempt);
 		}
 
-- 
2.52.0.223.gf5cc29aaa4-goog