From: Rik van Riel <riel@redhat.com>

Date: Fri, 23 Jun 2017 12:55:27 -0400

Subject: [PATCH] sched/numa: Override part of migrate_degrades_locality() when

 idle balancing

References: bnc#1060662

Patch-mainline: v4.12.1

Git-commit: 739294fb03f590401bbd7faa6d31a507e3ffada5

commit 739294fb03f590401bbd7faa6d31a507e3ffada5 upstream.

Several tests in the NAS benchmark seem to run a lot slower with

NUMA balancing enabled, than with NUMA balancing disabled. The

slower run time corresponds with increased idle time.

Overriding the final test of migrate_degrades_locality (but still

doing the other NUMA tests first) seems to improve performance

of those benchmarks.

Reported-by: Jirka Hladky <jhladky@redhat.com>

Signed-off-by: Rik van Riel <riel@redhat.com>

Cc: Linus Torvalds <torvalds@linux-foundation.org>

Cc: Mel Gorman <mgorman@suse.de>

Cc: Mike Galbraith <efault@gmx.de>

Cc: Peter Zijlstra <peterz@infradead.org>

Cc: Thomas Gleixner <tglx@linutronix.de>

Cc: linux-kernel@vger.kernel.org

Link: http://lkml.kernel.org/r/20170623165530.22514-2-riel@redhat.com

Signed-off-by: Ingo Molnar <mingo@kernel.org>

Signed-off-by: Mel Gorman <mgorman@techsingularity.net>

Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Signed-off-by: Jiri Slaby <jslaby@suse.cz>

---

 kernel/sched/fair.c | 4 ++++

 1 file changed, 4 insertions(+)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c

index 2c89ad8a3eba..58f2228f4820 100644

--- a/kernel/sched/fair.c

+++ b/kernel/sched/fair.c

@@ -6661,6 +6661,10 @@ static int migrate_degrades_locality(struct task_struct *p, struct lb_env *env)

 	if (dst_nid == p->numa_preferred_nid)

 		return 0;

+	/* Leaving a core idle is often worse than degrading locality. */

+	if (env->idle != CPU_NOT_IDLE)

+		return -1;

+

 	if (numa_group) {

 		src_faults = group_faults(p, src_nid);

 		dst_faults = group_faults(p, dst_nid);

-- 

2.14.2