[PATCH 6/9] sched/fair: Simplify wake_affine() for the single socket case

[Mel Gorman <mgorman@techsingularity.net>]

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>
---
 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 bbf45ed4a370..c82ac75547d5 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -5399,6 +5399,13 @@ 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:
@@ -6012,11 +6019,15 @@ 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);
 
-- 
2.13.1