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From:   =?UTF-8?B?56a56Iif6ZSu?= <ufo19890607@gmail.com>
Date:   Tue, 12 Feb 2019 11:14:10 +0800
Message-ID: <CAHCio2ggaG9gCB642=GgwfM2iCRm+ZcAp0HGqevJtVrRmnKPUA@mail.gmail.com>
Subject: Re: [PATCH] sched/debug: Show intergroup and hierarchy sum wait time
 of a task group
To:     Peter Zijlstra <peterz@infradead.org>
Cc:     mingo@redhat.com,
        =?UTF-8?B?546L6LSH?= <yun.wang@linux.alibaba.com>,
        Wind Yu <yuzhoujian@didichuxing.com>,
        linux-kernel@vger.kernel.org
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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@infradead.org> =E4=BA=8E2019=E5=B9=B42=E6=9C=887=E6=
=97=A5=E5=91=A8=E5=9B=9B =E4=B8=8A=E5=8D=881:19=E5=86=99=E9=81=93=EF=BC=9A
>
> On Wed, Jan 23, 2019 at 05:46:56PM +0800, ufo19890607@gmail.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 =3D cfs_rq_of(se);
> > +
> > +             if (cfs_rq->tg !=3D &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 :/