[PATCH 2/4] sched: simplify wake_affine for single socket case

From: riel
Date: Fri Jun 23 2017 - 12:56:21 EST


From: Rik van Riel <riel@xxxxxxxxxx>

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@xxxxxxxxxx>
---
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