Messages in this thread | | | Date | Thu, 06 Jul 2017 23:44:09 -0700 | From | Vikram Mulukutla <> | Subject | Re: [PATCH v2 4/6] cpufreq: schedutil: update CFS util only if used |
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On 2017-07-04 10:34, Patrick Bellasi wrote: > Currently the utilization of the FAIR class is collected before locking > the policy. Although that should not be a big issue for most cases, we > also don't really know how much latency there can be between the > utilization reading and its usage. > > Let's get the FAIR utilization right before its usage to be better in > sync with the current status of a CPU. > > Signed-off-by: Patrick Bellasi <patrick.bellasi@arm.com> > Cc: Ingo Molnar <mingo@redhat.com> > Cc: Peter Zijlstra <peterz@infradead.org> > Cc: Rafael J. Wysocki <rafael.j.wysocki@intel.com> > Cc: Viresh Kumar <viresh.kumar@linaro.org> > Cc: linux-kernel@vger.kernel.org > Cc: linux-pm@vger.kernel.org > --- > kernel/sched/cpufreq_schedutil.c | 3 +-- > 1 file changed, 1 insertion(+), 2 deletions(-) > > diff --git a/kernel/sched/cpufreq_schedutil.c > b/kernel/sched/cpufreq_schedutil.c > index 98704d8..df433f1 100644 > --- a/kernel/sched/cpufreq_schedutil.c > +++ b/kernel/sched/cpufreq_schedutil.c > @@ -308,10 +308,9 @@ static void sugov_update_shared(struct > update_util_data *hook, u64 time, > if (unlikely(current == sg_policy->thread)) > return; > > - sugov_get_util(&util, &max); > - > raw_spin_lock(&sg_policy->update_lock); > > + sugov_get_util(&util, &max); > sg_cpu->util = util; > sg_cpu->max = max;
Given that the utilization update hooks are called with the per-cpu rq lock held (for all classes), I don't think PELT utilization can change throughout the lifetime of the cpufreq_update_{util,this_cpu} call? Even with Viresh's remote cpu callback series we'd still have to hold the rq lock across cpufreq_update_util.. what can change today is 'max' (arch_scale_cpu_capacity) when a cpufreq policy is shared, so the patch is still needed for that reason I think?
Thanks, Vikram
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