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Date: Thu, 18 Aug 2016 22:03:13 -0700 From: Steve Muckle <steve.muckle@...aro.org> To: Wanpeng Li <kernellwp@...il.com> Cc: Steve Muckle <steve.muckle@...aro.org>, Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, Linux PM list <linux-pm@...r.kernel.org>, "Rafael J . Wysocki" <rafael@...nel.org>, Vincent Guittot <vincent.guittot@...aro.org>, Morten Rasmussen <morten.rasmussen@....com>, Dietmar Eggemann <dietmar.eggemann@....com>, Juri Lelli <Juri.Lelli@....com>, Patrick Bellasi <patrick.bellasi@....com> Subject: Re: [PATCH] sched: fix incorrect PELT values on SMT On Fri, Aug 19, 2016 at 10:30:36AM +0800, Wanpeng Li wrote: > 2016-08-19 9:55 GMT+08:00 Steve Muckle <steve.muckle@...aro.org>: > > PELT scales its util_sum and util_avg values via > > arch_scale_cpu_capacity(). If that function is passed the CPU's sched > > domain then it will reduce the scaling capacity if SD_SHARE_CPUCAPACITY > > is set. PELT does not pass in the sd however. The other caller of > > arch_scale_cpu_capacity, update_cpu_capacity(), does. This means > > util_sum and util_avg scale beyond the CPU capacity on SMT. > > > > On an Intel i7-3630QM for example rq->cpu_capacity_orig is 589 but > > util_avg scales up to 1024. > > > > Fix this by passing in the sd in __update_load_avg() as well. > > I believe we notice this at least several months ago. > https://lkml.org/lkml/2016/5/25/228 Glad to see I'm not alone in thinking this is an issue. It causes an issue with schedutil, effectively doubling the apparent demand on SMT. I don't know the load balance code well enough offhand to say whether it's an issue there. cheers, Steve
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