From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dietmar Eggemann Subject: Re: [PATCH 1/2] sched/fair: move cpufreq hook to update_cfs_rq_load_avg() Date: Mon, 28 Mar 2016 20:30:46 +0200 Message-ID: <56F97856.4040804@arm.com> References: <1458606068-7476-1-git-send-email-smuckle@linaro.org> <56F91D56.4020007@arm.com> <56F95D10.4070400@linaro.org> Mime-Version: 1.0 Content-Type: text/plain; charset="windows-1252"; format=flowed Content-Transfer-Encoding: 7bit Return-path: Received: from mail-am1on0095.outbound.protection.outlook.com ([157.56.112.95]:25846 "EHLO emea01-am1-obe.outbound.protection.outlook.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752879AbcC1UFK (ORCPT ); Mon, 28 Mar 2016 16:05:10 -0400 In-Reply-To: <56F95D10.4070400@linaro.org> Sender: linux-pm-owner@vger.kernel.org List-Id: linux-pm@vger.kernel.org To: Steve Muckle , Peter Zijlstra , Ingo Molnar Cc: linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org, "Rafael J. Wysocki" , Vincent Guittot , Morten Rasmussen , Juri Lelli , Patrick Bellasi , Michael Turquette 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