From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756516AbdLPCgr (ORCPT ); Fri, 15 Dec 2017 21:36:47 -0500 Received: from cloudserver094114.home.net.pl ([79.96.170.134]:42936 "EHLO cloudserver094114.home.net.pl" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756090AbdLPCgo (ORCPT ); Fri, 15 Dec 2017 21:36:44 -0500 From: "Rafael J. Wysocki" To: Patrick Bellasi Cc: linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org, Ingo Molnar , Peter Zijlstra , "Rafael J . Wysocki" , Viresh Kumar , Vincent Guittot , Paul Turner , Dietmar Eggemann , Morten Rasmussen , Juri Lelli , Todd Kjos , Joel Fernandes Subject: Re: [PATCH v2 4/4] sched/cpufreq_schedutil: use util_est for OPP selection Date: Sat, 16 Dec 2017 03:35:58 +0100 Message-ID: <1730241.78TPuThRce@aspire.rjw.lan> In-Reply-To: <20171205171018.9203-5-patrick.bellasi@arm.com> References: <20171205171018.9203-1-patrick.bellasi@arm.com> <20171205171018.9203-5-patrick.bellasi@arm.com> MIME-Version: 1.0 Content-Transfer-Encoding: 7Bit Content-Type: text/plain; charset="us-ascii" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tuesday, December 5, 2017 6:10:18 PM CET Patrick Bellasi wrote: > When schedutil looks at the CPU utilization, the current PELT value for > that CPU is returned straight away. In certain scenarios this can have > undesired side effects and delays on frequency selection. > > For example, since the task utilization is decayed at wakeup time, a > long sleeping big task newly enqueued does not add immediately a > significant contribution to the target CPU. This introduces some latency > before schedutil will be able to detect the best frequency required by > that task. > > Moreover, the PELT signal build-up time is function of the current > frequency, because of the scale invariant load tracking support. Thus, > starting from a lower frequency, the utilization build-up time will > increase even more and further delays the selection of the actual > frequency which better serves the task requirements. > > In order to reduce these kind of latencies, this patch integrates the > usage of the CPU's estimated utilization in the sugov_get_util function. > > The estimated utilization of a CPU is defined to be the maximum between > its PELT's utilization and the sum of the estimated utilization of each > currently RUNNABLE task on that CPU. > This allows to properly represent the expected utilization of a CPU which, > for example, has just got a big task running after a long sleep period, > and ultimately it allows to select the best frequency to run a task > right after it wakes up. > > Signed-off-by: Patrick Bellasi > Reviewed-by: Brendan Jackman > Reviewed-by: Dietmar Eggemann > Cc: Ingo Molnar > Cc: Peter Zijlstra > Cc: Rafael J. Wysocki > Cc: Viresh Kumar > Cc: Paul Turner > Cc: Vincent Guittot > Cc: Morten Rasmussen > Cc: Dietmar Eggemann > Cc: linux-kernel@vger.kernel.org > Cc: linux-pm@vger.kernel.org > > --- > Changes v1->v2: > - rebase on top of v4.15-rc2 > - tested that overhauled PELT code does not affect the util_est > --- > kernel/sched/cpufreq_schedutil.c | 6 +++++- > 1 file changed, 5 insertions(+), 1 deletion(-) > > diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c > index 2f52ec0f1539..465430d99440 100644 > --- a/kernel/sched/cpufreq_schedutil.c > +++ b/kernel/sched/cpufreq_schedutil.c > @@ -183,7 +183,11 @@ static void sugov_get_util(unsigned long *util, unsigned long *max, int cpu) > > cfs_max = arch_scale_cpu_capacity(NULL, cpu); > > - *util = min(rq->cfs.avg.util_avg, cfs_max); > + *util = rq->cfs.avg.util_avg; I would use a local variable here. That *util everywhere looks a bit dirtyish. > + if (sched_feat(UTIL_EST)) > + *util = max(*util, rq->cfs.util_est_runnable); > + *util = min(*util, cfs_max); > + > *max = cfs_max; > } > >