linux-kernel - [tip:sched/urgent] sched/fair: Fix wake_affine

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Date:   Thu, 7 Sep 2017 01:16:24 -0700
From:   tip-bot for Peter Zijlstra <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     luto@...nel.org, efault@....de, mingo@...nel.org,
        chris@...is-wilson.co.uk, linux-kernel@...r.kernel.org,
        hpa@...or.com, torvalds@...ux-foundation.org, peterz@...radead.org,
        tglx@...utronix.de
Subject: [tip:sched/urgent] sched/fair: Fix wake_affine_llc() balancing
 rules

Commit-ID:  a731ebe6f17bff9e7ca12ef227f9da4d5bdf8425
Gitweb:     http://git.kernel.org/tip/a731ebe6f17bff9e7ca12ef227f9da4d5bdf8425
Author:     Peter Zijlstra <peterz@...radead.org>
AuthorDate: Wed, 6 Sep 2017 12:51:31 +0200
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Thu, 7 Sep 2017 09:29:31 +0200

sched/fair: Fix wake_affine_llc() balancing rules

Chris Wilson reported that the SMT balance rules got the +1 on the
wrong side, resulting in a bias towards the current LLC; which the
load-balancer would then try and undo.

Reported-by: Chris Wilson <chris@...is-wilson.co.uk>
Tested-by: Chris Wilson <chris@...is-wilson.co.uk>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Cc: Andy Lutomirski <luto@...nel.org>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Mike Galbraith <efault@....de>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: linux-kernel@...r.kernel.org
Fixes: 90001d67be2f ("sched/fair: Fix wake_affine() for !NUMA_BALANCING")
Link: http://lkml.kernel.org/r/20170906105131.gqjmaextmn3u6tj2@hirez.programming.kicks-ass.net
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 8d58687..9dd2ce1 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -5435,7 +5435,7 @@ wake_affine_llc(struct sched_domain *sd, struct task_struct *p,
 		return false;
 
 	/* if this cache has capacity, come here */
-	if (this_stats.has_capacity && this_stats.nr_running < prev_stats.nr_running+1)
+	if (this_stats.has_capacity && this_stats.nr_running+1 < prev_stats.nr_running)
 		return true;
 
 	/*