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Groups > linux.kernel > #1605699
| From | "Rafael J. Wysocki" <rjw@rjwysocki.net> |
|---|---|
| Newsgroups | linux.kernel |
| Subject | Re: [RFC][PATCH v2 2/2] cpufreq: schedutil: Avoid decreasing frequency of busy CPUs |
| Date | 2017-03-21 16:10 +0100 |
| Message-ID | <tntA7-4ZS-47@gated-at.bofh.it> (permalink) |
| References | <tmJnz-6kS-3@gated-at.bofh.it> <tntgJ-4Dp-11@gated-at.bofh.it> <tntqq-4H9-25@gated-at.bofh.it> |
| Organization | linux.* mail to news gateway |
On Tuesday, March 21, 2017 03:46:07 PM Rafael J. Wysocki wrote:
> On Tuesday, March 21, 2017 02:38:42 PM Patrick Bellasi wrote:
> > 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 <peterz@infradead.org> wrote:
> > > > > On Tue, Mar 21, 2017 at 09:50:28AM +0100, Vincent Guittot wrote:
> > > > >> On 20 March 2017 at 22:46, Rafael J. Wysocki <rjw@rjwysocki.net> 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.
>
> Good point.
>
> > Previous solution was better IMO, apart from using overloaded instead
> > of overutilized (which is not yet there) :-/
>
> OK, so the one below works too.
Admittedly, we could check the idle condition and the overload flag at the same
time, though.
Let me try that too.
Thanks,
Rafael
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[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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