Messages in this thread | | | From | Joel Fernandes <> | Date | Thu, 6 Jul 2017 22:58:31 -0700 | Subject | Re: [PATCH v2 4/6] cpufreq: schedutil: update CFS util only if used |
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On Tue, Jul 4, 2017 at 10:34 AM, Patrick Bellasi <patrick.bellasi@arm.com> 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;
Is your concern that there will we spinlock contention before calling sugov_get_util?
If that's the case, with your patch it seems to me such contention (and hence spinning) itself could cause the utilization to be inflated - thus calling sugov_get_util after acquiring the lock will not be as accurate as before. In that case it seems to me its better to let sugov_get_util be called before acquiring the lock (as before).
thanks,
-Joel
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