linux-kernel - Re: [PATCH v3 4/4] sched: adjust sleeper credit for SCHED

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Date:   Tue, 24 Aug 2021 16:16:24 +0800
From:   Jiang Biao <benbjiang@...il.com>
To:     Josh Don <joshdon@...gle.com>
Cc:     Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Paul Turner <pjt@...gle.com>,
        Oleg Rombakh <olegrom@...gle.com>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Steve Sistare <steven.sistare@...cle.com>,
        Tejun Heo <tj@...nel.org>, Rik van Riel <riel@...riel.com>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 4/4] sched: adjust sleeper credit for SCHED_IDLE entities

Hi,

On Fri, 20 Aug 2021 at 09:06, Josh Don <joshdon@...gle.com> wrote:
>
> Give reduced sleeper credit to SCHED_IDLE entities. As a result, woken
> SCHED_IDLE entities will take longer to preempt normal entities.
>
> The benefit of this change is to make it less likely that a newly woken
> SCHED_IDLE entity will preempt a short-running normal entity before it
> blocks.
>
> We still give a small sleeper credit to SCHED_IDLE entities, so that
> idle<->idle competition retains some fairness.
>
> Example: With HZ=1000, spawned four threads affined to one cpu, one of
> which was set to SCHED_IDLE. Without this patch, wakeup latency for the
> SCHED_IDLE thread was ~1-2ms, with the patch the wakeup latency was
> ~5ms.
>
> Signed-off-by: Josh Don <joshdon@...gle.com>
Tried to push a similar patch before, but failed. :)
https://lkml.org/lkml/2020/8/20/1773
Please pick my Reviewed-by if you don't mind,
Reviewed-by: Jiang Biao <benbjiang@...cent.com>

> ---
>  kernel/sched/fair.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 31f40aa005b9..aa9c046d2aab 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -4230,7 +4230,12 @@ place_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int initial)
>
>         /* sleeps up to a single latency don't count. */
>         if (!initial) {
> -               unsigned long thresh = sysctl_sched_latency;
> +               unsigned long thresh;
> +
> +               if (se_is_idle(se))
> +                       thresh = sysctl_sched_min_granularity;
> +               else
> +                       thresh = sysctl_sched_latency;
>
>                 /*
>                  * Halve their sleep time's effect, to allow
> --
> 2.33.0.rc2.250.ged5fa647cd-goog
>