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

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Date:   Tue, 19 Feb 2019 10:15:14 +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

PING

禹舟键 <ufo19890607@...il.com> 于2019年2月12日周二 上午11:14写道：
>
> 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 :/