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Date: Thu, 3 Nov 2022 13:44:12 +0100 From: Peter Zijlstra <peterz@...radead.org> To: Chen Yu <yu.c.chen@...el.com> Cc: Vincent Guittot <vincent.guittot@...aro.org>, Tim Chen <tim.c.chen@...el.com>, Mel Gorman <mgorman@...hsingularity.net>, Juri Lelli <juri.lelli@...hat.com>, Rik van Riel <riel@...riel.com>, Aaron Lu <aaron.lu@...el.com>, Abel Wu <wuyun.abel@...edance.com>, K Prateek Nayak <kprateek.nayak@....com>, Yicong Yang <yangyicong@...ilicon.com>, "Gautham R . Shenoy" <gautham.shenoy@....com>, Ingo Molnar <mingo@...hat.com>, Dietmar Eggemann <dietmar.eggemann@....com>, Steven Rostedt <rostedt@...dmis.org>, Ben Segall <bsegall@...gle.com>, Daniel Bristot de Oliveira <bristot@...hat.com>, Valentin Schneider <vschneid@...hat.com>, Hillf Danton <hdanton@...a.com>, Honglei Wang <wanghonglei@...ichuxing.com>, Len Brown <len.brown@...el.com>, Chen Yu <yu.chen.surf@...il.com>, linux-kernel@...r.kernel.org Subject: Re: [RFC PATCH v2 1/2] sched/fair: Introduce short duration task check On Sun, Oct 23, 2022 at 11:32:31PM +0800, Chen Yu wrote: > + if (sched_feat(SIS_SHORT) && !prev->on_rq) { > + /* > + * sum_exec_runtime has been updated in update_curr() > + * because we reach here via dequeue. > + */ > + this_dur_avg = se->sum_exec_runtime - se->prev_sum_runtime_vol; > + /* > + * Record the accumulated runtime when task voluntarily > + * switches out. End of old duration period, a new period > + * starts. > + */ > + se->prev_sum_runtime_vol = se->sum_exec_runtime; > + > + last_dur_avg = se->dur_avg; > + delta = this_dur_avg - last_dur_avg; > + /* consider large change to avoid frequent update */ > + if (abs(delta) >= sysctl_sched_min_granularity) { > + /* > + * If it is the first time the task starts to > + * record dur_avg, discard the initial value 0. > + * Otherwise, calculate the EWMA. > + */ > + if (unlikely(!this_dur_avg)) > + se->dur_avg = this_dur_avg; > + else > + update_avg(&se->dur_avg, this_dur_avg); > + } > + } This seems excessively convoluted; what's wrong with something like: if (sched_feat(SIS_SHORT) && !prev->on_rq) { u64 this_dur = se->sum_exec_runtime - se->prev_sum_exec_runtime_vol; se->prev_sum_exec_runtime_vol = se->sum_exec_runtime; update_avg(&se->dur_avg, this_dur); } All that other stuff just makes it unreadable and probably slower.
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