linux-kernel - [patch 6/6] sched: set skip_clock_update in yield_task

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Date:	Fri, 18 Nov 2011 16:23:26 +0100
From:	Mike Galbraith <efault@....de>
To:	Suresh Siddha <suresh.b.siddha@...el.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...e.hu>, Paul Turner <pjt@...gle.com>
Subject: [patch 6/6] 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>

---
 kernel/sched.c      |    8 +++++++-
 kernel/sched_fair.c |    6 ++++++
 2 files changed, 13 insertions(+), 1 deletion(-)

Index: linux-3.2.git/kernel/sched.c
===================================================================
--- linux-3.2.git.orig/kernel/sched.c
+++ linux-3.2.git/kernel/sched.c
@@ -5838,7 +5838,13 @@ 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:
 	double_rq_unlock(rq, p_rq);
Index: linux-3.2.git/kernel/sched_fair.c
===================================================================
--- linux-3.2.git.orig/kernel/sched_fair.c
+++ linux-3.2.git/kernel/sched_fair.c
@@ -2688,6 +2688,12 @@ static void yield_task_fair(struct rq *r
 		 * 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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