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References: <20230222080314.2146-1-xuewen.yan@unisoc.com>
In-Reply-To: <20230222080314.2146-1-xuewen.yan@unisoc.com>
From:   Xuewen Yan <xuewen.yan94@gmail.com>
Date:   Mon, 27 Feb 2023 09:51:55 +0800
Message-ID: <CAB8ipk-+i98-RyWvYnz+OVyf8d=GR5zE2s7++q9t5-Geo4UFhw@mail.gmail.com>
Subject: Re: [RFC PATCH] sched/fair: update the vruntime to be max vruntime
 when yield
To:     Xuewen Yan <xuewen.yan@unisoc.com>
Cc:     vincent.guittot@linaro.org, mingo@redhat.com, peterz@infradead.org,
        juri.lelli@redhat.com, dietmar.eggemann@arm.com,
        rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de,
        bristot@redhat.com, vschneid@redhat.com, qyousef@layalina.io,
        linux-kernel@vger.kernel.org, ke.wang@unisoc.com,
        zhaoyang.huang@unisoc.com
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Hi all

Looking forward to your comments.

Thanks=EF=BC=81

On Wed, Feb 22, 2023 at 4:21 PM Xuewen Yan <xuewen.yan@unisoc.com> wrote:
>
> When task call the sched_yield, cfs would set the cfs's skip buddy.
> If there is no other task call the sched_yield syscall, the task would
> always be skiped when there are tasks in rq. As a result, the task's
> vruntime would not be updated for long time, and the cfs's min_vruntime
> is almost not updated.
> When this scenario happens, when the yield task had wait for a long time,
> and other tasks run a long time, once there is other task call the sched_=
yield,
> the cfs's skip_buddy is covered, at this time, the first task can run nor=
mally,
> but the task's vruntime is small, as a result, the task would always run,
> because other task's vruntime is big. This would lead to other tasks can =
not
> run for a long time.
> In order to mitigate this, update the yield_task's vruntime to be cfs's m=
ax vruntime.
> This way, the cfs's min vruntime can be updated as the process running.
>
> Signed-off-by: Xuewen Yan <xuewen.yan@unisoc.com>
> ---
>  kernel/sched/fair.c | 16 +++++++++++++---
>  1 file changed, 13 insertions(+), 3 deletions(-)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index ff4dbbae3b10..a9ff1921fc07 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -670,7 +670,6 @@ static struct sched_entity *__pick_next_entity(struct=
 sched_entity *se)
>         return __node_2_se(next);
>  }
>
> -#ifdef CONFIG_SCHED_DEBUG
>  struct sched_entity *__pick_last_entity(struct cfs_rq *cfs_rq)
>  {
>         struct rb_node *last =3D rb_last(&cfs_rq->tasks_timeline.rb_root)=
;
> @@ -681,6 +680,7 @@ struct sched_entity *__pick_last_entity(struct cfs_rq=
 *cfs_rq)
>         return __node_2_se(last);
>  }
>
> +#ifdef CONFIG_SCHED_DEBUG
>  /**************************************************************
>   * Scheduling class statistics methods:
>   */
> @@ -7751,8 +7751,18 @@ static void set_next_buddy(struct sched_entity *se=
)
>
>  static void set_skip_buddy(struct sched_entity *se)
>  {
> -       for_each_sched_entity(se)
> -               cfs_rq_of(se)->skip =3D se;
> +       for_each_sched_entity(se) {
> +               struct sched_entity *last;
> +               struct cfs_rq *cfs_rq =3D cfs_rq_of(se);
> +
> +               last =3D __pick_last_entity(cfs_rq);
> +               if (last) {
> +                       se->vruntime =3D last->vruntime;
> +                       update_min_vruntime(cfs_rq);
> +               }
> +
> +               cfs_rq->skip =3D se;
> +       }
>  }
>
>  /*
> --
> 2.25.1
>