linux-kernel - [PATCH] sched: resched proper CPU on yield

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Date:	Tue,  1 Mar 2011 16:28:21 -0800
From:	Venkatesh Pallipadi <venki@...gle.com>
To:	Mike Galbraith <efault@....de>, Rik van Riel <riel@...hat.com>,
	a.p.zijlstra@...llo.nl
Cc:	mingo@...hat.com, hpa@...or.com, linux-kernel@...r.kernel.org,
	mtosatti@...hat.com, tglx@...utronix.de, mingo@...e.hu,
	Venkatesh Pallipadi <venki@...gle.com>
Subject: [PATCH] sched: resched proper CPU on yield_to

yield_to_task_fair() has code to resched the CPU of yielding task when the
intention is to resched the CPU of the task that is being yielded to.

Change here fixes the problem and also makes the resched conditional on
rq != p_rq.

I don't have a setup to test this code path. So, this is only compile tested
right now.

Signed-off-by: Venkatesh Pallipadi <venki@...gle.com>
---
 kernel/sched.c      |    9 ++++++++-
 kernel/sched_fair.c |    4 ----
 2 files changed, 8 insertions(+), 5 deletions(-)

diff --git a/kernel/sched.c b/kernel/sched.c
index 5fb5aa2..afdbd09 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -5495,8 +5495,15 @@ again:
 		goto out;
 
 	yielded = curr->sched_class->yield_to_task(rq, p, preempt);
-	if (yielded)
+	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_task(p_rq->curr);
+	}
 
 out:
 	double_rq_unlock(rq, p_rq);
diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index 36e8f02..1b1c780 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -2001,10 +2001,6 @@ static bool yield_to_task_fair(struct rq *rq, struct task_struct *p, bool preemp
 	/* Tell the scheduler that we'd really like pse to run next. */
 	set_next_buddy(se);
 
-	/* Make p's CPU reschedule; pick_next_entity takes care of fairness. */
-	if (preempt)
-		resched_task(rq->curr);
-
 	yield_task_fair(rq);
 
 	return true;
-- 
1.7.3.1

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