linux-kernel - [tip:sched/core] sched/numa: Override part of migrate_degrades

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Date:   Sat, 24 Jun 2017 00:22:16 -0700
From:   tip-bot for Rik van Riel <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     jhladky@...hat.com, linux-kernel@...r.kernel.org,
        torvalds@...ux-foundation.org, peterz@...radead.org,
        mingo@...nel.org, tglx@...utronix.de, efault@....de,
        riel@...hat.com, hpa@...or.com, mgorman@...e.de
Subject: [tip:sched/core] sched/numa: Override part of
 migrate_degrades_locality() when idle balancing

Commit-ID:  739294fb03f590401bbd7faa6d31a507e3ffada5
Gitweb:     http://git.kernel.org/tip/739294fb03f590401bbd7faa6d31a507e3ffada5
Author:     Rik van Riel <riel@...hat.com>
AuthorDate: Fri, 23 Jun 2017 12:55:27 -0400
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Sat, 24 Jun 2017 08:57:46 +0200

sched/numa: Override part of migrate_degrades_locality() when idle balancing

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@...hat.com>
Signed-off-by: Rik van Riel <riel@...hat.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Mel Gorman <mgorman@...e.de>
Cc: Mike Galbraith <efault@....de>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: linux-kernel@...r.kernel.org
Link: http://lkml.kernel.org/r/20170623165530.22514-2-riel@redhat.com
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 kernel/sched/fair.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 694c258..6e0c052 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6688,6 +6688,10 @@ 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);