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Date: Mon, 28 Mar 2016 20:30:46 +0200 From: Dietmar Eggemann <dietmar.eggemann@....com> To: Steve Muckle <steve.muckle@...aro.org>, Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com> CC: <linux-kernel@...r.kernel.org>, <linux-pm@...r.kernel.org>, "Rafael J. Wysocki" <rafael@...nel.org>, Vincent Guittot <vincent.guittot@...aro.org>, Morten Rasmussen <morten.rasmussen@....com>, Juri Lelli <Juri.Lelli@....com>, Patrick Bellasi <patrick.bellasi@....com>, Michael Turquette <mturquette@...libre.com> Subject: Re: [PATCH 1/2] sched/fair: move cpufreq hook to update_cfs_rq_load_avg() On 03/28/2016 06:34 PM, Steve Muckle wrote: > Hi Dietmar, > > On 03/28/2016 05:02 AM, Dietmar Eggemann wrote: >> Hi Steve, >> >> these patches fall into the bucket of 'optimization of updating the >> value only if the root cfs_rq util has changed' as discussed in '[PATCH >> 5/8] sched/cpufreq: pass sched class into cpufreq_update_util' of Mike >> T's current series '[PATCH 0/8] schedutil enhancements', right? > > I would say just the second patch is an optimization. The first and > third patches cover additional paths in CFS where the hook should be > called but currently is not, which I think is a correctness issue. Not disagreeing here but I don't know if this level of accuracy is really needed. I mean we currently miss updates in enqueue_task_fair()->enqueue_entity()->enqueue_entity_load_avg() and idle_balance()/rebalance_domains()->update_blocked_averages() but there are plenty of call sides of update_load_avg(se, ...) with '&rq_of(cfs_rq_of(se))->cfs == cfs_rq_of(se)'. The question for me is does schedutil work better with this new, more accurate signal? IMO, not receiving a bunch of consecutive cpufreq_update_util's w/ the same 'util' value is probably a good thing, unless we see the interaction with RT/DL class as mentioned by Sai. Here an agreement on the design for the 'capacity vote aggregation from CFS/RT/DL' would help to clarify. >> I wonder if it makes sense to apply them before a proper 'capacity vote >> aggregation from CFS/RT/DL' has been agreed upon? > > Getting the right call sites for the hook in CFS should be orthogonal to > the sched class vote aggregation IMO. Hopefully :-) [...] Cheers, -- Dietmar
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