From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753186AbdK3QCk (ORCPT ); Thu, 30 Nov 2017 11:02:40 -0500 Received: from usa-sjc-mx-foss1.foss.arm.com ([217.140.101.70]:56814 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750885AbdK3QCj (ORCPT ); Thu, 30 Nov 2017 11:02:39 -0500 Date: Thu, 30 Nov 2017 16:02:34 +0000 From: Patrick Bellasi To: Juri Lelli Cc: linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org, Ingo Molnar , Peter Zijlstra , "Rafael J . Wysocki" , Viresh Kumar , Vincent Guittot , Dietmar Eggemann , Morten Rasmussen , Todd Kjos , Joel Fernandes Subject: Re: [PATCH v3 6/6] cpufreq: schedutil: ignore sugov kthreads Message-ID: <20171130160234.GG31247@e110439-lin> References: <20171130114723.29210-1-patrick.bellasi@arm.com> <20171130114723.29210-7-patrick.bellasi@arm.com> <20171130134155.GF9903@localhost.localdomain> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20171130134155.GF9903@localhost.localdomain> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 30-Nov 14:41, Juri Lelli wrote: > Hi, > > On 30/11/17 11:47, Patrick Bellasi wrote: > > In system where multiple CPUs shares the same frequency domain a small > > workload on a CPU can still be subject to frequency spikes, generated by > > the activation of the sugov's kthread. > > > > Since the sugov kthread is a special RT task, which goal is just that to > > activate a frequency transition, it does not make sense for it to bias > > the schedutil's frequency selection policy. > > > > This patch exploits the information related to the current task to silently > > ignore cpufreq_update_this_cpu() calls, coming from the RT scheduler, while > > the sugov kthread is running. > > > > Signed-off-by: Patrick Bellasi > > Reviewed-by: Dietmar Eggemann > > Cc: Ingo Molnar > > Cc: Peter Zijlstra > > Cc: Rafael J. Wysocki > > Cc: Viresh Kumar > > Cc: linux-kernel@vger.kernel.org > > Cc: linux-pm@vger.kernel.org > > > > --- > > Changes from v2: > > - rebased on v4.15-rc1 > > - moved at the end of the stack since considered more controversial > > Changes from v1: > > - move check before policy spinlock (JuriL) > > > > Change-Id: I4d749458229b6496dd24a8c357be42cd35a739fd > > --- > > kernel/sched/cpufreq_schedutil.c | 8 ++++++++ > > 1 file changed, 8 insertions(+) > > > > diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c > > index 3eea8884e61b..a93ad5b0c40d 100644 > > --- a/kernel/sched/cpufreq_schedutil.c > > +++ b/kernel/sched/cpufreq_schedutil.c > > @@ -270,6 +270,10 @@ static void sugov_update_single(struct update_util_data *hook, u64 time, > > bool rt_mode; > > bool busy; > > > > + /* Skip updates generated by sugov kthreads */ > > + if (unlikely(current == sg_policy->thread)) > > + return; > > + > > sugov_set_iowait_boost(sg_cpu, time, flags); > > sg_cpu->last_update = time; > > > > @@ -356,6 +360,10 @@ static void sugov_update_shared(struct update_util_data *hook, u64 time, > > unsigned int next_f; > > bool rt_mode; > > > > + /* Skip updates generated by sugov kthreads */ > > + if (unlikely(current == sg_policy->thread)) > > + return; > > + > > raw_spin_lock(&sg_policy->update_lock); > > > > sugov_get_util(&util, &max, sg_cpu->cpu); > > If the DL changes (which I shall post again as soon as tip/sched/core is > bumped up to 4.15-rc1) get in first, this is going to be useless (as the > DL kthread gets ignored by the scheduling class itself). But, this looks > good to me "in the meantime". Just to better understand, you mean that the DL kthread does not send out schedutil updates? If that's the case I agree we can discard this patch... that's also one of the reasons why I move it at the end of this series. > Reviewed-by: Juri Lelli > > Best, > > Juri -- #include Patrick Bellasi