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Subject[tip:sched/core] sched/fair: Simplify wake_affine() for the single socket case
Commit-ID:  7d894e6e34a5cdd12309c7e4a3f830277ad4b7bf
Gitweb: http://git.kernel.org/tip/7d894e6e34a5cdd12309c7e4a3f830277ad4b7bf
Author: Rik van Riel <riel@redhat.com>
AuthorDate: Fri, 23 Jun 2017 12:55:28 -0400
Committer: Ingo Molnar <mingo@kernel.org>
CommitDate: Sat, 24 Jun 2017 08:57:52 +0200

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

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>
---
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 6e0c052..fe19016 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -5420,6 +5420,13 @@ 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:
@@ -6007,11 +6014,15 @@ 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);

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