Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932871AbdCUOpq (ORCPT ); Tue, 21 Mar 2017 10:45:46 -0400 Received: from foss.arm.com ([217.140.101.70]:53694 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932660AbdCUOpo (ORCPT ); Tue, 21 Mar 2017 10:45:44 -0400 Date: Tue, 21 Mar 2017 14:38:42 +0000 From: Patrick Bellasi To: "Rafael J. Wysocki" Cc: Vincent Guittot , Peter Zijlstra , Linux PM , LKML , Srinivas Pandruvada , Viresh Kumar , Juri Lelli , Joel Fernandes , Morten Rasmussen , Ingo Molnar Subject: Re: [RFC][PATCH v2 2/2] cpufreq: schedutil: Avoid decreasing frequency of busy CPUs Message-ID: <20170321143842.GE11054@e110439-lin> References: <4366682.tsferJN35u@aspire.rjw.lan> <20170321132253.vjp7f72qkubpttmf@hirez.programming.kicks-ass.net> <3429350.K2FUBgvcIK@aspire.rjw.lan> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <3429350.K2FUBgvcIK@aspire.rjw.lan> 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 Content-Length: 5086 Lines: 119 On 21-Mar 15:26, Rafael J. Wysocki wrote: > On Tuesday, March 21, 2017 02:37:08 PM Vincent Guittot wrote: > > On 21 March 2017 at 14:22, Peter Zijlstra wrote: > > > On Tue, Mar 21, 2017 at 09:50:28AM +0100, Vincent Guittot wrote: > > >> On 20 March 2017 at 22:46, Rafael J. Wysocki wrote: > > > > > >> > To work around this issue use the observation that, from the > > >> > schedutil governor's perspective, it does not make sense to decrease > > >> > the frequency of a CPU that doesn't enter idle and avoid decreasing > > >> > the frequency of busy CPUs. > > >> > > >> I don't fully agree with that statement. > > >> If there are 2 runnable tasks on CPU A and scheduler migrates the > > >> waiting task to another CPU B so CPU A is less loaded now, it makes > > >> sense to reduce the OPP. That's even for that purpose that we have > > >> decided to use scheduler metrics in cpufreq governor so we can adjust > > >> OPP immediately when tasks migrate. > > >> That being said, i probably know why you see such OPP switches in your > > >> use case. When we migrate a task, we also migrate/remove its > > >> utilization from CPU. > > >> If the CPU is not overloaded, it means that runnable tasks have all > > >> computation that they need and don't have any reason to use more when > > >> a task migrates to another CPU. so decreasing the OPP makes sense > > >> because the utilzation is decreasing > > >> If the CPU is overloaded, it means that runnable tasks have to share > > >> CPU time and probably don't have all computations that they would like > > >> so when a task migrate, the remaining tasks on the CPU will increase > > >> their utilization and fill space left by the task that has just > > >> migrated. So the CPU's utilization will decrease when a task migrates > > >> (and as a result the OPP) but then its utilization will increase with > > >> remaining tasks running more time as well as the OPP > > >> > > >> So you need to make the difference between this 2 cases: Is a CPU > > >> overloaded or not. You can't really rely on the utilization to detect > > >> that but you could take advantage of the load which take into account > > >> the waiting time of tasks > > > > > > I'm confused. What two cases? You only list the overloaded case, but he > > > > overloaded vs not overloaded use case. > > For the not overloaded case, it makes sense to immediately update to > > OPP to be aligned with the new utilization of the CPU even if it was > > not idle in the past couple of ticks > > Yes, if the OPP (or P-state if you will) can be changed immediately. If it can't, > conditions may change by the time we actually update it and in that case It'd > be better to wait and see IMO. > > In any case, the theory about migrating tasks made sense to me, so below is > what I tested. It works, and besides it has a nice feature that I don't need > to fetch for the timekeeping data. :-) > > I only wonder if we want to do this or only prevent the frequency from > decreasing in the overloaded case? > > --- > kernel/sched/cpufreq_schedutil.c | 8 +++++--- > 1 file changed, 5 insertions(+), 3 deletions(-) > > Index: linux-pm/kernel/sched/cpufreq_schedutil.c > =================================================================== > --- linux-pm.orig/kernel/sched/cpufreq_schedutil.c > +++ linux-pm/kernel/sched/cpufreq_schedutil.c > @@ -61,6 +61,7 @@ struct sugov_cpu { > unsigned long util; > unsigned long max; > unsigned int flags; > + bool overload; > }; > > static DEFINE_PER_CPU(struct sugov_cpu, sugov_cpu); > @@ -207,7 +208,7 @@ static void sugov_update_single(struct u > if (!sugov_should_update_freq(sg_policy, time)) > return; > > - if (flags & SCHED_CPUFREQ_RT_DL) { > + if ((flags & SCHED_CPUFREQ_RT_DL) || this_rq()->rd->overload) { > next_f = policy->cpuinfo.max_freq; Isn't this going to max OPP every time we have more than 1 task in that CPU? In that case it will not fit the case: we have two 10% tasks on that CPU. Previous solution was better IMO, apart from using overloaded instead of overutilized (which is not yet there) :-/ > } else { > sugov_get_util(&util, &max); > @@ -242,7 +243,7 @@ static unsigned int sugov_next_freq_shar > j_sg_cpu->iowait_boost = 0; > continue; > } > - if (j_sg_cpu->flags & SCHED_CPUFREQ_RT_DL) > + if ((j_sg_cpu->flags & SCHED_CPUFREQ_RT_DL) || j_sg_cpu->overload) > return policy->cpuinfo.max_freq; > > j_util = j_sg_cpu->util; > @@ -273,12 +274,13 @@ static void sugov_update_shared(struct u > sg_cpu->util = util; > sg_cpu->max = max; > sg_cpu->flags = flags; > + sg_cpu->overload = this_rq()->rd->overload; > > sugov_set_iowait_boost(sg_cpu, time, flags); > sg_cpu->last_update = time; > > if (sugov_should_update_freq(sg_policy, time)) { > - if (flags & SCHED_CPUFREQ_RT_DL) > + if ((flags & SCHED_CPUFREQ_RT_DL) || sg_cpu->overload) > next_f = sg_policy->policy->cpuinfo.max_freq; > else > next_f = sugov_next_freq_shared(sg_cpu); > -- #include Patrick Bellasi