linux-kernel - Re: [PATCH v2] sched/fair: merge same code in enqueue_task

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Date:   Wed, 13 Dec 2023 09:24:36 +0100
From:   Vincent Guittot <vincent.guittot@...aro.org>
To:     Abel Wu <wuyun.abel@...edance.com>
Cc:     WangJinchao <wangjinchao@...sion.com>,
        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>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Valentin Schneider <vschneid@...hat.com>,
        linux-kernel@...r.kernel.org, stone.xulei@...sion.com
Subject: Re: [PATCH v2] sched/fair: merge same code in enqueue_task_fair

On Wed, 13 Dec 2023 at 09:19, Abel Wu <wuyun.abel@...edance.com> wrote:
>
> Hi Jinchao,
>
> On 12/13/23 3:12 PM, WangJinchao Wrote:
> > The code below is duplicated in two for loops and need to be
> >     consolidated
>
> It doesn't need to, but it can actually bring some benefit from
> the point of view of text size, especially in warehouse-scale
> computers where icache is extremely contended.
>
> add/remove: 0/0 grow/shrink: 0/1 up/down: 0/-56 (-56)
> Function                                     old     new   delta
> enqueue_task_fair                            936     880     -56
> Total: Before=64899, After=64843, chg -0.09%
>
> >
> > Signed-off-by: WangJinchao <wangjinchao@...sion.com>
> > ---
> >   kernel/sched/fair.c | 31 ++++++++-----------------------
> >   1 file changed, 8 insertions(+), 23 deletions(-)
> >
> > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> > index d7a3c63a2171..e1373bfd4f2e 100644
> > --- a/kernel/sched/fair.c
> > +++ b/kernel/sched/fair.c
> > @@ -6681,30 +6681,15 @@ enqueue_task_fair(struct rq *rq, struct task_struct *p, int flags)
> >               cpufreq_update_util(rq, SCHED_CPUFREQ_IOWAIT);
> >
> >       for_each_sched_entity(se) {
> > -             if (se->on_rq)
> > -                     break;
> >               cfs_rq = cfs_rq_of(se);
> > -             enqueue_entity(cfs_rq, se, flags);
> > -
> > -             cfs_rq->h_nr_running++;
> > -             cfs_rq->idle_h_nr_running += idle_h_nr_running;
> > -
> > -             if (cfs_rq_is_idle(cfs_rq))
> > -                     idle_h_nr_running = 1;
> > -
> > -             /* end evaluation on encountering a throttled cfs_rq */
> > -             if (cfs_rq_throttled(cfs_rq))
> > -                     goto enqueue_throttle;
> > -
> > -             flags = ENQUEUE_WAKEUP;
> > -     }
> > -
> > -     for_each_sched_entity(se) {
> > -             cfs_rq = cfs_rq_of(se);
> > -
> > -             update_load_avg(cfs_rq, se, UPDATE_TG);
> > -             se_update_runnable(se);
> > -             update_cfs_group(se);
> > +             if (se->on_rq) {
> > +                     update_load_avg(cfs_rq, se, UPDATE_TG);
> > +                     se_update_runnable(se);
> > +                     update_cfs_group(se);
> > +             } else {
> > +                     enqueue_entity(cfs_rq, se, flags);
> > +                     flags = ENQUEUE_WAKEUP;
> > +             }
> >
> >               cfs_rq->h_nr_running++;
> >               cfs_rq->idle_h_nr_running += idle_h_nr_running;
>
> I have no strong opinon about this 'cleanup', but the same pattern
> can also be found in dequeue_task_fair() and I think it would be
> better get them synchronized.

I agree, I don't see any benefit from this change

>
> Thanks,
>         Abel