linux-kernel - [PATCH 4.12 22/27] sched/fair: Simplify wake

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Date:   Mon, 10 Jul 2017 19:10:19 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Rik van Riel <riel@...hat.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Mel Gorman <mgorman@...e.de>, Mike Galbraith <efault@....de>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>, jhladky@...hat.com,
        Ingo Molnar <mingo@...nel.org>,
        Mel Gorman <mgorman@...hsingularity.net>
Subject: [PATCH 4.12 22/27] sched/fair: Simplify wake_affine() for the single socket case

4.12-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Rik van Riel <riel@...hat.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@...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: jhladky@...hat.com
Cc: linux-kernel@...r.kernel.org
Link: http://lkml.kernel.org/r/20170623165530.22514-3-riel@redhat.com
Signed-off-by: Ingo Molnar <mingo@...nel.org>
Signed-off-by: Mel Gorman <mgorman@...hsingularity.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.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);