linux-kernel - [PATCH v3 17/57] sched: Simplify yield

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Message-ID: <20230612093538.712217968@infradead.org>
Date:   Mon, 12 Jun 2023 11:07:30 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     torvalds@...ux-foundation.org, keescook@...omium.org,
        gregkh@...uxfoundation.org, pbonzini@...hat.com
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Subject: [PATCH v3 17/57] sched: Simplify yield_to()

Use guards to reduce gotos and simplify control flow.

Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
 kernel/sched/core.c |   73 ++++++++++++++++++++++------------------------------
 1 file changed, 32 insertions(+), 41 deletions(-)

--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -8799,55 +8799,46 @@ int __sched yield_to(struct task_struct
 {
 	struct task_struct *curr = current;
 	struct rq *rq, *p_rq;
-	unsigned long flags;
 	int yielded = 0;
 
-	local_irq_save(flags);
-	rq = this_rq();
+	scoped_guard (irqsave) {
+		rq = this_rq();
 
 again:
-	p_rq = task_rq(p);
-	/*
-	 * If we're the only runnable task on the rq and target rq also
-	 * has only one task, there's absolutely no point in yielding.
-	 */
-	if (rq->nr_running == 1 && p_rq->nr_running == 1) {
-		yielded = -ESRCH;
-		goto out_irq;
-	}
-
-	double_rq_lock(rq, p_rq);
-	if (task_rq(p) != p_rq) {
-		double_rq_unlock(rq, p_rq);
-		goto again;
-	}
-
-	if (!curr->sched_class->yield_to_task)
-		goto out_unlock;
-
-	if (curr->sched_class != p->sched_class)
-		goto out_unlock;
-
-	if (task_on_cpu(p_rq, p) || !task_is_running(p))
-		goto out_unlock;
-
-	yielded = curr->sched_class->yield_to_task(rq, p);
-	if (yielded) {
-		schedstat_inc(rq->yld_count);
+		p_rq = task_rq(p);
 		/*
-		 * Make p's CPU reschedule; pick_next_entity takes care of
-		 * fairness.
+		 * If we're the only runnable task on the rq and target rq also
+		 * has only one task, there's absolutely no point in yielding.
 		 */
-		if (preempt && rq != p_rq)
-			resched_curr(p_rq);
-	}
+		if (rq->nr_running == 1 && p_rq->nr_running == 1)
+			return -ESRCH;
 
-out_unlock:
-	double_rq_unlock(rq, p_rq);
-out_irq:
-	local_irq_restore(flags);
+		guard(double_rq_lock)(rq, p_rq);
+		if (task_rq(p) != p_rq)
+			goto again;
+
+		if (!curr->sched_class->yield_to_task)
+			return 0;
+
+		if (curr->sched_class != p->sched_class)
+			return 0;
+
+		if (task_on_cpu(p_rq, p) || !task_is_running(p))
+			return 0;
+
+		yielded = curr->sched_class->yield_to_task(rq, p);
+		if (yielded) {
+			schedstat_inc(rq->yld_count);
+			/*
+			 * Make p's CPU reschedule; pick_next_entity
+			 * takes care of fairness.
+			 */
+			if (preempt && rq != p_rq)
+				resched_curr(p_rq);
+		}
+	}
 
-	if (yielded > 0)
+	if (yielded)
 		schedule();
 
 	return yielded;