linux-kernel - Re: [PATCH] sched/debug: Show intergroup and hierarchy sum wait time of a task group

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Message-ID: <CAHCio2ggaG9gCB642=GgwfM2iCRm+ZcAp0HGqevJtVrRmnKPUA@mail.gmail.com>
Date:   Tue, 12 Feb 2019 11:14:10 +0800
From:   禹舟键 <ufo19890607@...il.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     mingo@...hat.com,
        王贇 <yun.wang@...ux.alibaba.com>,
        Wind Yu <yuzhoujian@...ichuxing.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] sched/debug: Show intergroup and hierarchy sum wait time
 of a task group

Hi, Peter
I think hierarchy wait time for task groups is worth accounting
despite with a little extra overhead. Because we can evaluate task
groups' condition with a more direct metric. We cannot get the real
situation just with some general metrics, like idle or loadavg, since
their value is decreased with the elapse of time. So, I think general
metrics cannot satisify the request for task groups.

Thanks
Yuzhoujian


Peter Zijlstra <peterz@...radead.org> 于2019年2月7日周四 上午1:19写道：
>
> On Wed, Jan 23, 2019 at 05:46:56PM +0800, ufo19890607@...il.com wrote:
> > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> > index e2ff4b6..35e89ca 100644
> > --- a/kernel/sched/fair.c
> > +++ b/kernel/sched/fair.c
> > @@ -858,6 +858,19 @@ static void update_curr_fair(struct rq *rq)
> >  }
> >
> >  static inline void
> > +update_hierarchy_wait_sum(struct sched_entity *se,
> > +                     u64 delta_wait)
> > +{
> > +     for_each_sched_entity(se) {
> > +             struct cfs_rq *cfs_rq = cfs_rq_of(se);
> > +
> > +             if (cfs_rq->tg != &root_task_group)
> > +                     __schedstat_add(cfs_rq->hierarchy_wait_sum,
> > +                                     delta_wait);
> > +     }
> > +}
> > +
> > +static inline void
> >  update_stats_wait_end(struct cfs_rq *cfs_rq, struct sched_entity *se)
> >  {
> >       struct task_struct *p;
> > @@ -880,6 +893,7 @@ static void update_curr_fair(struct rq *rq)
> >                       return;
> >               }
> >               trace_sched_stat_wait(p, delta);
> > +             update_hierarchy_wait_sum(se, delta);
> >       }
> >
> >       __schedstat_set(se->statistics.wait_max,
>
> The problem I have with this is that it will make schedstats even more
> expensive :/