linux-kernel - [PATCH 3/4] sched: Comment on why sync wakeups try to run on the current CPU

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Message-Id: <20171218094327.19562-4-mgorman@techsingularity.net>
Date:   Mon, 18 Dec 2017 09:43:26 +0000
From:   Mel Gorman <mgorman@...hsingularity.net>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Ingo Molnar <mingo@...hat.com>,
        Matt Fleming <matt@...eblueprint.co.uk>,
        Mel Gorman <mgorman@...hsingularity.net>,
        LKML <linux-kernel@...r.kernel.org>
Subject: [PATCH 3/4] sched: Comment on why sync wakeups try to run on the current CPU

The sync wakeup logic in wake_affine_idle deserves a short description.

Signed-off-by: Mel Gorman <mgorman@...hsingularity.net>
---
 kernel/sched/fair.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 392e08b364bd..95b1145bc38d 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -5737,6 +5737,11 @@ wake_affine_idle(int this_cpu, int prev_cpu, int sync)
 static int
 wake_affine_sync(int this_cpu, int sync)
 {
+	/*
+	 * Consider stacking tasks if it's a sync wakeup and there is only
+	 * one task on the runqueue. sync wakesups are expected to sleep
+	 * either immediately or shortly after the wakeup.
+	 */
 	if (sync && cpu_rq(this_cpu)->nr_running == 1)
 		return this_cpu;
 
-- 
2.15.0