[tip:sched/core] sched: Call select_idle_sibling() when not affine_sd

[tip-bot for Rik van Riel <tipbot@zytor.com>]

Commit-ID:  8bf21433f38b020c3d8a3805d1d7fb73d7b40c01
Gitweb:     http://git.kernel.org/tip/8bf21433f38b020c3d8a3805d1d7fb73d7b40c01
Author:     Rik van Riel <riel@redhat.com>
AuthorDate: Wed, 14 May 2014 11:40:37 -0400
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Thu, 22 May 2014 11:16:28 +0200

sched: Call select_idle_sibling() when not affine_sd

On smaller systems, the top level sched domain will be an affine
domain, and select_idle_sibling is invoked for every SD_WAKE_AFFINE
wakeup. This seems to be working well.

On larger systems, with the node distance between far away NUMA nodes
being > RECLAIM_DISTANCE, select_idle_sibling is only called if the
waker and the wakee are on nodes less than RECLAIM_DISTANCE apart.

This patch leaves in place the policy of not pulling the task across
nodes on such systems, while fixing the issue that select_idle_sibling
is not called at all in certain circumstances.

The code will look for an idle CPU in the same CPU package as the
CPU where the task ran previously.

Signed-off-by: Rik van Riel <riel@redhat.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Cc: morten.rasmussen@arm.com
Cc: george.mccollister@gmail.com
Cc: ktkhai@parallels.com
Cc: Mel Gorman <mgorman@suse.de>
Cc: Mike Galbraith <umgwanakikbuti@gmail.com>
Link: http://lkml.kernel.org/r/20140514114037.2d93266f@annuminas.surriel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 kernel/sched/fair.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index dd3fa14..429164d 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -4473,10 +4473,10 @@ select_task_rq_fair(struct task_struct *p, int prev_cpu, int sd_flag, int wake_f
 			sd = tmp;
 	}
 
-	if (affine_sd) {
-		if (cpu != prev_cpu && wake_affine(affine_sd, p, sync))
-			prev_cpu = cpu;
+	if (affine_sd && cpu != prev_cpu && wake_affine(affine_sd, p, sync))
+		prev_cpu = cpu;
 
+	if (sd_flag & SD_BALANCE_WAKE) {
 		new_cpu = select_idle_sibling(p, prev_cpu);
 		goto unlock;
 	}