linux-kernel - Re: [PATCH] sched/fair: Rearrange select_task_rq

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Date:   Wed, 25 Apr 2018 10:45:09 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Valentin Schneider <valentin.schneider@....com>,
        Ingo Molnar <mingo@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        linux-kernel@...r.kernel.org,
        Quentin Perret <quentin.perret@....com>,
        c@...ez.programming.kicks-ass.net
Subject: Re: [PATCH] sched/fair: Rearrange select_task_rq_fair() to optimize
 it

On 24-04-18, 14:35, Peter Zijlstra wrote:
> In any case, if there not going to be conflicts here, this all looks
> good.

Thanks Peter.

I also had another patch and wasn't sure if that would be the right
thing to do. The main purpose of this is to avoid calling
sync_entity_load_avg() unnecessarily.

+++ b/kernel/sched/fair.c
@@ -6196,9 +6196,6 @@ static inline int find_idlest_cpu(struct sched_domain *sd, struct task_struct *p
 {
        int new_cpu = cpu;
 
-       if (!cpumask_intersects(sched_domain_span(sd), &p->cpus_allowed))
-               return prev_cpu;
-
        while (sd) {
                struct sched_group *group;
                struct sched_domain *tmp;
@@ -6652,15 +6649,19 @@ select_task_rq_fair(struct task_struct *p, int prev_cpu, int sd_flag, int wake_f
        if (unlikely(sd)) {
                /* Slow path */
 
-               /*
-                * We're going to need the task's util for capacity_spare_wake
-                * in find_idlest_group. Sync it up to prev_cpu's
-                * last_update_time.
-                */
-               if (!(sd_flag & SD_BALANCE_FORK))
-                       sync_entity_load_avg(&p->se);
+               if (!cpumask_intersects(sched_domain_span(sd), &p->cpus_allowed)) {
+                       new_cpu = prev_cpu;
+               } else {
+                       /*
+                        * We're going to need the task's util for
+                        * capacity_spare_wake in find_idlest_group. Sync it up
+                        * to prev_cpu's last_update_time.
+                        */
+                       if (!(sd_flag & SD_BALANCE_FORK))
+                               sync_entity_load_avg(&p->se);
 
-               new_cpu = find_idlest_cpu(sd, p, cpu, prev_cpu, sd_flag);
+                       new_cpu = find_idlest_cpu(sd, p, cpu, prev_cpu, sd_flag);
+               }
        } else if (sd_flag & SD_BALANCE_WAKE) { /* XXX always ? */
                /* Fast path */

-- 
viresh