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>

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 6e0c052..fe19016 100644 (file)
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -5419,6 +5419,13 @@ static int wake_affine(struct sched_domain *sd, struct task_struct *p,
        load      = source_load(prev_cpu, idx);
        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
@@ -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);