linux-kernel - [PATCH 2/4] sched: simplify wake

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Date:   Fri, 23 Jun 2017 12:55:28 -0400
From:   riel@...hat.com
To:     linux-kernel@...r.kernel.org
Cc:     jhladky@...hat.com, mingo@...nel.org, mgorman@...e.de,
        peterz@...radead.org
Subject: [PATCH 2/4] sched: simplify wake_affine for single socket case

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

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

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 2180c8591e16..949de24e36bd 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -5373,6 +5373,13 @@ static int wake_affine(struct sched_domain *sd, struct task_struct *p,
 	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:
@@ -5960,11 +5967,15 @@ select_task_rq_fair(struct task_struct *p, int prev_cpu, int sd_flag, int wake_f
 
 	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);
 
-- 
2.9.4