Patch "sched/fair: Simplify wake_affine() for the single socket case" has been added to the 4.12-stable tree

Patch "sched/fair: Simplify wake_affine() for the single socket case" has been added to the 4.12-stable tree

[gregkh]

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

    sched/fair: Simplify wake_affine() for the single socket case

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-fair-simplify-wake_affine-for-the-single-socket-case.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 <stable@vger.kernel.org> know about it.


>From 7d894e6e34a5cdd12309c7e4a3f830277ad4b7bf Mon Sep 17 00:00:00 2001
From: Rik van Riel <riel@redhat.com>
Date: Fri, 23 Jun 2017 12:55:28 -0400
Subject: sched/fair: Simplify wake_affine() for the single socket case

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

commit 7d894e6e34a5cdd12309c7e4a3f830277ad4b7bf upstream.

Then 'this_cpu' and 'prev_cpu' are in the same socket, select_idle_sibling()
will do its thing regardless of the return value of wake_affine().

Just return true and don't look at all the other things.

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: jhladky@redhat.com
Cc: linux-kernel@vger.kernel.org
Link: http://lkml.kernel.org/r/20170623165530.22514-3-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>

---
 kernel/sched/fair.c |   13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -5399,6 +5399,13 @@ static int wake_affine(struct sched_doma
 	this_load = target_load(this_cpu, idx);
 
 	/*
+	 * Common case: CPUs are in the same socket, and select_idle_sibling()
+	 * will do its thing regardless of what we return:
+	 */
+	if (cpus_share_cache(prev_cpu, this_cpu))
+		return true;
+
+	/*
 	 * If sync wakeup then subtract the (maximum possible)
 	 * effect of the currently running task from the load
 	 * of the current CPU:
@@ -5986,11 +5993,15 @@ select_task_rq_fair(struct task_struct *
 
 	if (affine_sd) {
 		sd = NULL; /* Prefer wake_affine over balance flags */
-		if (cpu != prev_cpu && wake_affine(affine_sd, p, prev_cpu, sync))
+		if (cpu == prev_cpu)
+			goto pick_cpu;
+
+		if (wake_affine(affine_sd, p, prev_cpu, sync))
 			new_cpu = cpu;
 	}
 
 	if (!sd) {
+ pick_cpu:
 		if (sd_flag & SD_BALANCE_WAKE) /* XXX always ? */
 			new_cpu = select_idle_sibling(p, prev_cpu, new_cpu);
 


Patches currently in stable-queue which might be from riel@redhat.com 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