linux-kernel - Re: [PATCH v2 03/13] sched/fair: Optimize find_idlest

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Message-ID: <CAKfTPtCp7Yo-whLTqp4+SCGp-mGztLZV8+LncvT1cWepKWST9w@mail.gmail.com>
Date:	Wed, 13 Jul 2016 14:20:24 +0200
From:	Vincent Guittot <vincent.guittot@...aro.org>
To:	Morten Rasmussen <morten.rasmussen@....com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	"mingo@...hat.com" <mingo@...hat.com>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	Yuyang Du <yuyang.du@...el.com>, mgalbraith@...e.de,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 03/13] sched/fair: Optimize find_idlest_cpu() when
 there is no choice

On 22 June 2016 at 19:03, Morten Rasmussen <morten.rasmussen@....com> wrote:
> In the current find_idlest_group()/find_idlest_cpu() search we end up
> calling find_idlest_cpu() in a sched_group containing only one cpu in
> the end. Checking idle-states becomes pointless when there is no
> alternative, so bail out instead.
>
> cc: Ingo Molnar <mingo@...hat.com>
> cc: Peter Zijlstra <peterz@...radead.org>
>
> Signed-off-by: Morten Rasmussen <morten.rasmussen@....com>
> ---
>  kernel/sched/fair.c | 4 ++++
>  1 file changed, 4 insertions(+)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index eec8e29104f9..216db302e87d 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -5123,6 +5123,10 @@ find_idlest_cpu(struct sched_group *group, struct task_struct *p, int this_cpu)
>         int shallowest_idle_cpu = -1;
>         int i;
>
> +       /* Check if we have any choice */
> +       if (group->group_weight == 1)
> +               return cpumask_first(sched_group_cpus(group));
> +
>         /* Traverse only the allowed CPUs */
>         for_each_cpu_and(i, sched_group_cpus(group), tsk_cpus_allowed(p)) {
>                 if (idle_cpu(i)) {

FWIW, you can add my Acked-by: : Vincent Guittot <vincent.guittot@...aro.org>

> --
> 1.9.1
>