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Groups > linux.kernel > #1605546
| From | Patrick Bellasi <patrick.bellasi@arm.com> |
|---|---|
| Newsgroups | linux.kernel |
| Subject | Re: [RFC][PATCH v2 2/2] cpufreq: schedutil: Avoid decreasing frequency of busy CPUs |
| Date | 2017-03-21 13:00 +0100 |
| Message-ID | <tnqCe-2Qk-17@gated-at.bofh.it> (permalink) |
| References | <tmJnz-6kS-3@gated-at.bofh.it> <tmJnz-6kS-7@gated-at.bofh.it> <tndvk-2mG-19@gated-at.bofh.it> <tnnO1-Sm-1@gated-at.bofh.it> |
| Organization | linux.* mail to news gateway |
On 21-Mar 09:50, Vincent Guittot wrote:
> On 20 March 2017 at 22:46, Rafael J. Wysocki <rjw@rjwysocki.net> wrote:
> > From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> >
> > The way the schedutil governor uses the PELT metric causes it to
> > underestimate the CPU utilization in some cases.
> >
> > That can be easily demonstrated by running kernel compilation on
> > a Sandy Bridge Intel processor, running turbostat in parallel with
> > it and looking at the values written to the MSR_IA32_PERF_CTL
> > register. Namely, the expected result would be that when all CPUs
> > were 100% busy, all of them would be requested to run in the maximum
> > P-state, but observation shows that this clearly isn't the case.
> > The CPUs run in the maximum P-state for a while and then are
> > requested to run slower and go back to the maximum P-state after
> > a while again. That causes the actual frequency of the processor to
> > visibly oscillate below the sustainable maximum in a jittery fashion
> > which clearly is not desirable.
> >
> > 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
Right, we can use "overloaded" for the time being until we push the
"overutilized" bits.
[...]
> > +#ifdef CONFIG_NO_HZ_COMMON
> > +static bool sugov_cpu_is_busy(struct sugov_cpu *sg_cpu)
> > +{
> > + unsigned long idle_calls = tick_nohz_get_idle_calls();
> > + bool ret = idle_calls == sg_cpu->saved_idle_calls;
Vincent: are you proposing something like this?
+ if (this_rq()->rd->overload)
+ return false;
> > +
> > + sg_cpu->saved_idle_calls = idle_calls;
> > + return ret;
> > +}
> > +#else
> > +static inline bool sugov_cpu_is_busy(struct sugov_cpu *sg_cpu) { return false; }
> > +#endif /* CONFIG_NO_HZ_COMMON */
> > +
> > +static void sugov_update_commit(struct sugov_cpu *sg_cpu,
> > + struct sugov_policy *sg_policy,
> > + u64 time, unsigned int next_freq)
> > {
> > struct cpufreq_policy *policy = sg_policy->policy;
> >
> > + if (sugov_cpu_is_busy(sg_cpu) && next_freq < sg_policy->next_freq)
> > + next_freq = sg_policy->next_freq;
> > +
> > if (policy->fast_switch_enabled) {
> > if (sg_policy->next_freq == next_freq) {
> > trace_cpu_frequency(policy->cur, smp_processor_id());
> > @@ -214,7 +234,7 @@ static void sugov_update_single(struct u
> > sugov_iowait_boost(sg_cpu, &util, &max);
> > next_f = get_next_freq(sg_policy, util, max);
> > }
> > - sugov_update_commit(sg_policy, time, next_f);
> > + sugov_update_commit(sg_cpu, sg_policy, time, next_f);
> > }
> >
[...]
--
#include <best/regards.h>
Patrick Bellasi
Back to linux.kernel | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread
[PATCH 0/2] cpufreq: schedutil: Fix and optimization "Rafael J. Wysocki" <rjw@rjwysocki.net> - 2017-03-19 14:50 +0100
[PATCH 1/2] cpufreq: schedutil: Fix per-CPU structure initialization in sugov_start() "Rafael J. Wysocki" <rjw@rjwysocki.net> - 2017-03-19 14:50 +0100
Re: [PATCH 1/2] cpufreq: schedutil: Fix per-CPU structure initialization in sugov_start() Viresh Kumar <viresh.kumar@linaro.org> - 2017-03-20 04:30 +0100
Re: [PATCH 1/2] cpufreq: schedutil: Fix per-CPU structure initialization in sugov_start() "Rafael J. Wysocki" <rjw@rjwysocki.net> - 2017-03-20 13:50 +0100
[RFC][PATCH 2/2] cpufreq: schedutil: Force max frequency on busy CPUs "Rafael J. Wysocki" <rjw@rjwysocki.net> - 2017-03-19 14:50 +0100
Re: [RFC][PATCH 2/2] cpufreq: schedutil: Force max frequency on busy CPUs "Rafael J. Wysocki" <rjw@rjwysocki.net> - 2017-03-19 22:40 +0100
Re: [RFC][PATCH 2/2] cpufreq: schedutil: Force max frequency on busy CPUs "Rafael J. Wysocki" <rjw@rjwysocki.net> - 2017-03-19 22:50 +0100
Re: [RFC][PATCH 2/2] cpufreq: schedutil: Force max frequency on busy CPUs Peter Zijlstra <peterz@infradead.org> - 2017-03-20 12:10 +0100
Re: [RFC][PATCH 2/2] cpufreq: schedutil: Force max frequency on busy CPUs "Rafael J. Wysocki" <rjw@rjwysocki.net> - 2017-03-20 13:50 +0100
Re: [RFC][PATCH 2/2] cpufreq: schedutil: Force max frequency on busy CPUs Viresh Kumar <viresh.kumar@linaro.org> - 2017-03-20 05:00 +0100
Re: [RFC][PATCH 2/2] cpufreq: schedutil: Force max frequency on busy CPUs Vincent Guittot <vincent.guittot@linaro.org> - 2017-03-20 09:30 +0100
Re: [RFC][PATCH 2/2] cpufreq: schedutil: Force max frequency on busy CPUs Patrick Bellasi <patrick.bellasi@arm.com> - 2017-03-20 13:40 +0100
Re: [RFC][PATCH 2/2] cpufreq: schedutil: Force max frequency on busy CPUs Joel Fernandes <joelaf@google.com> - 2017-03-23 01:00 +0100
Re: [RFC][PATCH 2/2] cpufreq: schedutil: Force max frequency on busy CPUs Vincent Guittot <vincent.guittot@linaro.org> - 2017-03-23 23:10 +0100
Re: [RFC][PATCH 2/2] cpufreq: schedutil: Force max frequency on busy CPUs Joel Fernandes <joelaf@google.com> - 2017-03-25 04:50 +0100
Re: [RFC][PATCH 2/2] cpufreq: schedutil: Force max frequency on busy CPUs Vincent Guittot <vincent.guittot@linaro.org> - 2017-03-27 09:10 +0200
Re: [RFC][PATCH 2/2] cpufreq: schedutil: Force max frequency on busy CPUs "Rafael J. Wysocki" <rjw@rjwysocki.net> - 2017-03-20 14:10 +0100
Re: [RFC][PATCH 2/2] cpufreq: schedutil: Force max frequency on busy CPUs Vincent Guittot <vincent.guittot@linaro.org> - 2017-03-20 14:40 +0100
Re: [RFC][PATCH 2/2] cpufreq: schedutil: Force max frequency on busy CPUs "Rafael J. Wysocki" <rjw@rjwysocki.net> - 2017-03-20 14:30 +0100
Re: [RFC][PATCH 2/2] cpufreq: schedutil: Force max frequency on busy CPUs Peter Zijlstra <peterz@infradead.org> - 2017-03-20 12:50 +0100
Re: [RFC][PATCH 2/2] cpufreq: schedutil: Force max frequency on busy CPUs "Rafael J. Wysocki" <rjw@rjwysocki.net> - 2017-03-20 13:50 +0100
Re: [RFC][PATCH 2/2] cpufreq: schedutil: Force max frequency on busy CPUs Peter Zijlstra <peterz@infradead.org> - 2017-03-20 14:00 +0100
Re: [RFC][PATCH 2/2] cpufreq: schedutil: Force max frequency on busy CPUs Patrick Bellasi <patrick.bellasi@arm.com> - 2017-03-20 14:10 +0100
Re: [RFC][PATCH 2/2] cpufreq: schedutil: Force max frequency on busy CPUs "Rafael J. Wysocki" <rjw@rjwysocki.net> - 2017-03-20 14:40 +0100
Re: [RFC][PATCH 2/2] cpufreq: schedutil: Force max frequency on busy CPUs Patrick Bellasi <patrick.bellasi@arm.com> - 2017-03-20 15:20 +0100
Re: [RFC][PATCH 2/2] cpufreq: schedutil: Force max frequency on busy CPUs "Rafael J. Wysocki" <rjw@rjwysocki.net> - 2017-03-20 14:20 +0100
[RFC][PATCH v2 2/2] cpufreq: schedutil: Avoid decreasing frequency of busy CPUs "Rafael J. Wysocki" <rjw@rjwysocki.net> - 2017-03-20 23:00 +0100
Re: [RFC][PATCH v2 2/2] cpufreq: schedutil: Avoid decreasing frequency of busy CPUs Viresh Kumar <viresh.kumar@linaro.org> - 2017-03-21 07:50 +0100
Re: [RFC][PATCH v2 2/2] cpufreq: schedutil: Avoid decreasing frequency of busy CPUs "Rafael J. Wysocki" <rafael@kernel.org> - 2017-03-21 13:40 +0100
Re: [RFC][PATCH v2 2/2] cpufreq: schedutil: Avoid decreasing frequency of busy CPUs Vincent Guittot <vincent.guittot@linaro.org> - 2017-03-21 10:00 +0100
Re: [RFC][PATCH v2 2/2] cpufreq: schedutil: Avoid decreasing frequency of busy CPUs Patrick Bellasi <patrick.bellasi@arm.com> - 2017-03-21 13:00 +0100
Re: [RFC][PATCH v2 2/2] cpufreq: schedutil: Avoid decreasing frequency of busy CPUs Peter Zijlstra <peterz@infradead.org> - 2017-03-21 14:30 +0100
Re: [RFC][PATCH v2 2/2] cpufreq: schedutil: Avoid decreasing frequency of busy CPUs Vincent Guittot <vincent.guittot@linaro.org> - 2017-03-21 14:40 +0100
Re: [RFC][PATCH v2 2/2] cpufreq: schedutil: Avoid decreasing frequency of busy CPUs Vincent Guittot <vincent.guittot@linaro.org> - 2017-03-21 15:30 +0100
Re: [RFC][PATCH v2 2/2] cpufreq: schedutil: Avoid decreasing frequency of busy CPUs "Rafael J. Wysocki" <rjw@rjwysocki.net> - 2017-03-21 15:40 +0100
Re: [RFC][PATCH v2 2/2] cpufreq: schedutil: Avoid decreasing frequency of busy CPUs Patrick Bellasi <patrick.bellasi@arm.com> - 2017-03-21 15:50 +0100
Re: [RFC][PATCH v2 2/2] cpufreq: schedutil: Avoid decreasing frequency of busy CPUs "Rafael J. Wysocki" <rjw@rjwysocki.net> - 2017-03-21 16:00 +0100
Re: [RFC][PATCH v2 2/2] cpufreq: schedutil: Avoid decreasing frequency of busy CPUs Peter Zijlstra <peterz@infradead.org> - 2017-03-21 16:10 +0100
Re: [RFC][PATCH v2 2/2] cpufreq: schedutil: Avoid decreasing frequency of busy CPUs "Rafael J. Wysocki" <rjw@rjwysocki.net> - 2017-03-21 16:30 +0100
Re: [RFC][PATCH v2 2/2] cpufreq: schedutil: Avoid decreasing frequency of busy CPUs Peter Zijlstra <peterz@infradead.org> - 2017-03-21 18:10 +0100
Re: [RFC][PATCH v2 2/2] cpufreq: schedutil: Avoid decreasing frequency of busy CPUs "Rafael J. Wysocki" <rjw@rjwysocki.net> - 2017-03-21 18:30 +0100
Re: [RFC][PATCH v2 2/2] cpufreq: schedutil: Avoid decreasing frequency of busy CPUs Patrick Bellasi <patrick.bellasi@arm.com> - 2017-03-21 16:10 +0100
Re: [RFC][PATCH v2 2/2] cpufreq: schedutil: Avoid decreasing frequency of busy CPUs Peter Zijlstra <peterz@infradead.org> - 2017-03-21 16:20 +0100
Re: [RFC][PATCH v2 2/2] cpufreq: schedutil: Avoid decreasing frequency of busy CPUs Patrick Bellasi <patrick.bellasi@arm.com> - 2017-03-21 20:30 +0100
Re: [RFC][PATCH v2 2/2] cpufreq: schedutil: Avoid decreasing frequency of busy CPUs "Rafael J. Wysocki" <rjw@rjwysocki.net> - 2017-03-21 16:10 +0100
Re: [RFC][PATCH v2 2/2] cpufreq: schedutil: Avoid decreasing frequency of busy CPUs Peter Zijlstra <peterz@infradead.org> - 2017-03-21 16:10 +0100
Re: [RFC][PATCH v2 2/2] cpufreq: schedutil: Avoid decreasing frequency of busy CPUs Patrick Bellasi <patrick.bellasi@arm.com> - 2017-03-21 15:40 +0100
Re: [RFC][PATCH v2 2/2] cpufreq: schedutil: Avoid decreasing frequency of busy CPUs Peter Zijlstra <peterz@infradead.org> - 2017-03-21 16:00 +0100
Re: [RFC][PATCH v2 2/2] cpufreq: schedutil: Avoid decreasing frequency of busy CPUs Peter Zijlstra <peterz@infradead.org> - 2017-03-21 16:00 +0100
Re: [RFC][PATCH v2 2/2] cpufreq: schedutil: Avoid decreasing frequency of busy CPUs Vincent Guittot <vincent.guittot@linaro.org> - 2017-03-21 18:10 +0100
Re: [RFC][PATCH v2 2/2] cpufreq: schedutil: Avoid decreasing frequency of busy CPUs Vincent Guittot <vincent.guittot@linaro.org> - 2017-03-21 18:10 +0100
Re: [RFC][PATCH v2 2/2] cpufreq: schedutil: Avoid decreasing frequency of busy CPUs Patrick Bellasi <patrick.bellasi@arm.com> - 2017-03-21 13:00 +0100
[RFC][PATCH v3 2/2] cpufreq: schedutil: Avoid reducing frequency of busy CPUs prematurely "Rafael J. Wysocki" <rjw@rjwysocki.net> - 2017-03-22 00:20 +0100
Re: [RFC][PATCH v3 2/2] cpufreq: schedutil: Avoid reducing frequency of busy CPUs prematurely Peter Zijlstra <peterz@infradead.org> - 2017-03-22 10:30 +0100
Re: [RFC][PATCH v3 2/2] cpufreq: schedutil: Avoid reducing frequency of busy CPUs prematurely Viresh Kumar <viresh.kumar@linaro.org> - 2017-03-22 11:10 +0100
Re: [RFC][PATCH v3 2/2] cpufreq: schedutil: Avoid reducing frequency of busy CPUs prematurely Joel Fernandes <joelaf@google.com> - 2017-03-23 02:10 +0100
Re: [RFC][PATCH v3 2/2] cpufreq: schedutil: Avoid reducing frequency of busy CPUs prematurely Sai Gurrappadi <sgurrappadi@nvidia.com> - 2017-03-23 20:30 +0100
Re: [RFC][PATCH v3 2/2] cpufreq: schedutil: Avoid reducing frequency of busy CPUs prematurely Sai Gurrappadi <sgurrappadi@nvidia.com> - 2017-03-23 22:00 +0100
Re: [RFC][PATCH v3 2/2] cpufreq: schedutil: Avoid reducing frequency of busy CPUs prematurely "Rafael J. Wysocki" <rafael@kernel.org> - 2017-03-24 02:40 +0100
Re: [RFC][PATCH v3 2/2] cpufreq: schedutil: Avoid reducing frequency of busy CPUs prematurely Sai Gurrappadi <sgurrappadi@nvidia.com> - 2017-03-24 20:20 +0100
Re: [RFC][PATCH v3 2/2] cpufreq: schedutil: Avoid reducing frequency of busy CPUs prematurely Sai Gurrappadi <sgurrappadi@nvidia.com> - 2017-03-25 02:20 +0100
Re: [RFC][PATCH v3 2/2] cpufreq: schedutil: Avoid reducing frequency of busy CPUs prematurely "Rafael J. Wysocki" <rafael@kernel.org> - 2017-03-25 02:40 +0100
Re: [RFC][PATCH v3 2/2] cpufreq: schedutil: Avoid reducing frequency of busy CPUs prematurely Vincent Guittot <vincent.guittot@linaro.org> - 2017-03-27 09:20 +0200
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