linux-kernel - Re: [PATCH] sched/fair: avoid vruntime compensation for SCHED

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Date:   Thu, 20 Aug 2020 14:51:06 +0200
From:   Vincent Guittot <vincent.guittot@...aro.org>
To:     Jiang Biao <benbjiang@...il.com>
Cc:     Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.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>,
        Jiang Biao <benbjiang@...cent.com>
Subject: Re: [PATCH] sched/fair: avoid vruntime compensation for SCHED_IDLE task

On Thu, 20 Aug 2020 at 14:00, Jiang Biao <benbjiang@...il.com> wrote:
>
> From: Jiang Biao <benbjiang@...cent.com>
>
> Vruntime compensation has been down in place_entity() to
> boot the waking procedure for fair tasks. There is no need to

s/boot/boost/ ?

> do that for SCHED_IDLE task actually.
>
> Not compensating vruntime for SCHED_IDLE task could make
> SCHED_IDLE task more harmless for normal tasks.
>
> Signed-off-by: Jiang Biao <benbjiang@...cent.com>
> ---
>  kernel/sched/fair.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 1a68a0536add..adff77676a0a 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -4115,7 +4115,7 @@ place_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int initial)
>                 vruntime += sched_vslice(cfs_rq, se);
>
>         /* sleeps up to a single latency don't count. */
> -       if (!initial) {
> +       if (!initial && likely(!task_has_idle_policy(task_of(se)))) {

What if se is not a task ?

>                 unsigned long thresh = sysctl_sched_latency;
>
>                 /*
> --
> 2.21.0
>