linux-kernel - [PATCH] sched: release buddies on yield

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Date:	Tue, 11 Nov 2008 11:52:33 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Lin Ming <ming.m.lin@...el.com>
Cc:	Mike Galbraith <efault@....de>,
	"Zhang, Yanmin" <yanmin_zhang@...ux.intel.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Dhaval Giani <dhaval@...ux.vnet.ibm.com>,
	Miao Xie <miaox@...fujitsu.com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...e.hu>
Subject: [PATCH] sched: release buddies on yield

Clear buddies on yield, so that the buddy rules don't schedule them
despite them being placed right-most.

This fixed a performance regression with yield-happy binary JVMs.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
Tested-by: Lin Ming <ming.m.lin@...el.com>
---
 kernel/sched_fair.c |   17 ++++++++++++-----
 1 files changed, 12 insertions(+), 5 deletions(-)

diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index 51aa3e1..98345e4 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -716,6 +716,15 @@ enqueue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int wakeup)
 		__enqueue_entity(cfs_rq, se);
 }
 
+static void clear_buddies(struct cfs_rq *cfs_rq, struct sched_entity *se)
+{
+	if (cfs_rq->last == se)
+		cfs_rq->last = NULL;
+
+	if (cfs_rq->next == se)
+		cfs_rq->next = NULL;
+}
+
 static void
 dequeue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int sleep)
 {
@@ -738,11 +747,7 @@ dequeue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int sleep)
 #endif
 	}
 
-	if (cfs_rq->last == se)
-		cfs_rq->last = NULL;
-
-	if (cfs_rq->next == se)
-		cfs_rq->next = NULL;
+	clear_buddies(cfs_rq, se);
 
 	if (se != cfs_rq->curr)
 		__dequeue_entity(cfs_rq, se);
@@ -977,6 +982,8 @@ static void yield_task_fair(struct rq *rq)
 	if (unlikely(cfs_rq->nr_running == 1))
 		return;
 
+	clear_buddies(cfs_rq, se);
+
 	if (likely(!sysctl_sched_compat_yield) && curr->policy != SCHED_BATCH) {
 		update_rq_clock(rq);
 		/*

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