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Date: Fri, 9 Oct 2020 17:33:14 +0800 From: jun qian <qianjun.kernel@...il.com> To: Peter Zijlstra <peterz@...radead.org> Cc: mingo@...hat.com, Vincent Guittot <vincent.guittot@...aro.org>, juri.lelli@...hat.com, linux-kernel@...r.kernel.org, dietmar.eggemann@....com, rostedt@...dmis.org, Benjamin Segall <bsegall@...gle.com>, mgorman@...e.de, Yafang Shao <laoar.shao@...il.com> Subject: Re: [PATCH 1/1] sched/fair: Fix the wrong sched_stat_wait time jun qian <qianjun.kernel@...il.com> 于2020年9月30日周三 下午9:08写道: > > Peter Zijlstra <peterz@...radead.org> 于2020年9月30日周三 下午5:57写道: > > > > On Wed, Sep 30, 2020 at 05:16:29PM +0800, jun qian wrote: > > > Peter Zijlstra <peterz@...radead.org> 于2020年9月30日周三 下午4:20写道: > > > > > > > > On Wed, Sep 30, 2020 at 10:47:12AM +0800, qianjun.kernel@...il.com wrote: > > > > > From: jun qian <qianjun.kernel@...il.com> > > > > > > > > > > When the sched_schedstat changes from 0 to 1, some sched se maybe > > > > > already in the runqueue, the se->statistics.wait_start will be 0. > > > > > So it will let the (rq_of(cfs_rq)) - se->statistics.wait_start) > > > > > wrong. We need to avoid this scenario. > > > > > > > > Is this really the only problem there? Did you do a full audit of that > > > > schedstat nonsense? > > > > > > > > > > Did you mean that the sched_stat_xxx's xxx_start(sched_stat_sleep > > > sched_stat_iowait sched_stat_blocked > > > sched_stat_runtime) may be also depend the schedstat_enabled? > > > > Yeah, this runtime schedstat_enabled thing is fairly recent, it used to > > be an always on/off kinda thing. > > > > At the time we figured inconsistencies from dynamically > > enabling/disabling it were okay, it's just stats after all. > > > > But if you now want to 'fix' that, then a full audit might be nice. > > > > > I have searched the codes, and found that these sched_stat_xxx's > > > xxx_start don't depend the schedstat_enabled > > > except the wait_start. > > > > OK, so you did the audit and only found this one issue? That's good > > Changelog material :-) > > > > I found another problem, when the sched_schedstat changes from 1 to 0, > the sched se > which is already in the runqueue, the statistics.wait_start already > has a value. At this moment > sched_schedstat changes from 0 to 1 again, the (rq_of(cfs_rq)) - > se->statistics.wait_start) > will not be 0 and the wait time will be bigger than the real one. So > we need to modify the patch > to resolve the problem with this scenario. > hi Peter I have sent another patch to improve the accuracy of sched_stat_wait statistics. I have no good idea to solve the another problem what i described up, but the new patch can improve the accuracy. Thanks > So I really need a full audit might, :-) > > Thanks > > > Thanks!
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