linux-kernel - [tip:sched/core] sched/numa: Fix off-by-one in capacity check

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Date:	Tue, 12 Aug 2014 07:53:05 -0700
From:	tip-bot for Rik van Riel <tipbot@...or.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, riel@...hat.com, hpa@...or.com,
	mingo@...nel.org, torvalds@...ux-foundation.org,
	peterz@...radead.org, tglx@...utronix.de
Subject: [tip:sched/core] sched/numa: Fix off-by-one in capacity check

Commit-ID:  b932c03c34f3b03c7364c06aa8cae5b74609fc41
Gitweb:     http://git.kernel.org/tip/b932c03c34f3b03c7364c06aa8cae5b74609fc41
Author:     Rik van Riel <riel@...hat.com>
AuthorDate: Mon, 4 Aug 2014 13:23:27 -0400
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Tue, 12 Aug 2014 12:48:22 +0200

sched/numa: Fix off-by-one in capacity check

Commit a43455a1d572daf7b730fe12eb747d1e17411365 ensures that
task_numa_migrate will call task_numa_compare on the preferred
node all the time, even when the preferred node has no free capacity.

This could lead to a performance regression if nr_running == capacity
on both the source and the destination node. This can be avoided by
also checking for nr_running == capacity on the source node, which is
one stricter than checking .has_free_capacity.

Signed-off-by: Rik van Riel <riel@...hat.com>
Signed-off-by: Peter Zijlstra <peterz@...radead.org>
Cc: mgorman@...e.de
Cc: vincent.guittot@...aro.org
Cc: Morten.Rasmussen@....com
Cc: nicolas.pitre@...aro.org
Cc: efault@....de
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Link: http://lkml.kernel.org/r/1407173008-9334-2-git-send-email-riel@redhat.com
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 kernel/sched/fair.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index df1ed17..e1cf419 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -1206,7 +1206,7 @@ static void task_numa_compare(struct task_numa_env *env,
 
 	if (!cur) {
 		/* Is there capacity at our destination? */
-		if (env->src_stats.has_free_capacity &&
+		if (env->src_stats.nr_running <= env->src_stats.task_capacity &&
 		    !env->dst_stats.has_free_capacity)
 			goto unlock;
 
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