linux-kernel - Re: [PATCH] sched/fair: Simplify the code of should_we

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Date:   Tue, 14 Apr 2020 09:25:00 +0200
From:   Vincent Guittot <vincent.guittot@...aro.org>
To:     Peng Wang <rocking@...ux.alibaba.com>
Cc:     Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>, uri.lelli@...hat.com,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] sched/fair: Simplify the code of should_we_balance()

On Sat, 11 Apr 2020 at 11:21, Peng Wang <rocking@...ux.alibaba.com> wrote:
>
> We only consider group_balance_cpu() after there is no idle
> cpu. So, just do comparison before return at these two cases.
>
> Signed-off-by: Peng Wang <rocking@...ux.alibaba.com>

With the small fix in the comment below
Reviewed-by: Vincent Guittot <vincent.guittot@...aro.org>

> ---
>  kernel/sched/fair.c | 16 +++++-----------
>  1 file changed, 5 insertions(+), 11 deletions(-)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 1ea3ddd..81b2c647 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -9413,7 +9413,7 @@ static int active_load_balance_cpu_stop(void *data);
>  static int should_we_balance(struct lb_env *env)
>  {
>         struct sched_group *sg = env->sd->groups;
> -       int cpu, balance_cpu = -1;
> +       int cpu;
>
>         /*
>          * Ensure the balancing environment is consistent; can happen
> @@ -9434,18 +9434,12 @@ static int should_we_balance(struct lb_env *env)
>                 if (!idle_cpu(cpu))
>                         continue;
>
> -               balance_cpu = cpu;
> -               break;
> +               /* Are we the first idle CPU? */
> +               return cpu == env->dst_cpu;
>         }
>
> -       if (balance_cpu == -1)
> -               balance_cpu = group_balance_cpu(sg);
> -
> -       /*
> -        * First idle CPU or the first CPU(busiest) in this sched group
> -        * is eligible for doing load balancing at this and above domains.
> -        */
> -       return balance_cpu == env->dst_cpu;
> +       /* Are we the first balance CPU of this group? */

/* Are we the first CPU of this group ? */

> +       return group_balance_cpu(sg) == env->dst_cpu;
>  }
>
>  /*
> --
> 2.9.5
>