Patch "sched/numa: Override part of migrate_degrades_locality() when idle balancing" has been added to the 4.12-stable tree

This is a note to let you know that I've just added the patch titled

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

to the 4.12-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
sched-numa-override-part-of-migrate_degrades_locality-when-idle-balancing.patch
and it can be found in the queue-4.12 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Rik van Riel <[email protected]>
Date: Fri, 23 Jun 2017 12:55:27 -0400
Subject: sched/numa: Override part of migrate_degrades_locality() when idle balancing

From: Rik van Riel <[email protected]>

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.

---
 kernel/sched/fair.c |    4 ++++
 1 file changed, 4 insertions(+)

@@ -6661,6 +6661,10 @@ static int migrate_degrades_locality(str
 	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);

Patches currently in stable-queue which might be from [email protected] are

queue-4.12/sched-numa-hide-numa_wake_affine-from-up-build.patch queue-4.12/sched-numa-use-down_read_trylock-for-the-mmap_sem.patch queue-4.12/sched-core-implement-new-approach-to-scale-select_idle_cpu.patch queue-4.12/sched-fair-remove-effective_load.patch queue-4.12/sched-numa-implement-numa-node-level-wake_affine.patch queue-4.12/sched-fair-simplify-wake_affine-for-the-single-socket-case.patch queue-4.12/sched-fair-cpumask-export-for_each_cpu_wrap.patch queue-4.12/sched-numa-override-part-of-migrate_degrades_locality-when-idle-balancing.patch