linux-kernel - [tip:sched/core] sched: Set skip_clock_update in yield_task

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Date:	Tue, 6 Dec 2011 01:51:09 -0800
From:	tip-bot for Mike Galbraith <mgalbraith@...e.de>
To:	linux-tip-commits@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, mgalbraith@...e.de, hpa@...or.com,
	mingo@...hat.com, a.p.zijlstra@...llo.nl, efault@....de,
	tglx@...utronix.de, mingo@...e.hu
Subject: [tip:sched/core] sched: Set skip_clock_update in yield_task_fair()

Commit-ID:  916671c08b7808aebec87cc56c85788e665b3c6b
Gitweb:     http://git.kernel.org/tip/916671c08b7808aebec87cc56c85788e665b3c6b
Author:     Mike Galbraith <mgalbraith@...e.de>
AuthorDate: Tue, 22 Nov 2011 15:21:26 +0100
Committer:  Ingo Molnar <mingo@...e.hu>
CommitDate: Tue, 6 Dec 2011 09:06:24 +0100

sched: Set skip_clock_update in yield_task_fair()

This is another case where we are on our way to schedule(),
so can save a useless clock update and resulting microscopic
vruntime update.

Signed-off-by: Mike Galbraith <efault@....de>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
Link: http://lkml.kernel.org/r/1321971686.6855.18.camel@marge.simson.net
Signed-off-by: Ingo Molnar <mingo@...e.hu>
---
 kernel/sched/core.c |    7 +++++++
 kernel/sched/fair.c |    6 ++++++
 2 files changed, 13 insertions(+), 0 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index ca8fd44..db313c3 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -4547,6 +4547,13 @@ again:
 		 */
 		if (preempt && rq != p_rq)
 			resched_task(p_rq->curr);
+	} else {
+		/*
+		 * We might have set it in task_yield_fair(), but are
+		 * not going to schedule(), so don't want to skip
+		 * the next update.
+		 */
+		rq->skip_clock_update = 0;
 	}
 
 out:
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 8e534a0..81ccb81 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -3075,6 +3075,12 @@ static void yield_task_fair(struct rq *rq)
 		 * Update run-time statistics of the 'current'.
 		 */
 		update_curr(cfs_rq);
+		/*
+		 * Tell update_rq_clock() that we've just updated,
+		 * so we don't do microscopic update in schedule()
+		 * and double the fastpath cost.
+		 */
+		 rq->skip_clock_update = 1;
 	}
 
 	set_skip_buddy(se);
--
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