Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > linux.kernel > #1604525

Re: [RFC][PATCH 2/2] cpufreq: schedutil: Force max frequency on busy CPUs

From Peter Zijlstra <peterz@infradead.org>
Newsgroups linux.kernel
Subject Re: [RFC][PATCH 2/2] cpufreq: schedutil: Force max frequency on busy CPUs
Date 2017-03-20 14:00 +0100
Message-ID <tn54K-4Ra-17@gated-at.bofh.it> (permalink)
References <tmJnz-6kS-3@gated-at.bofh.it> <tmJnz-6kS-7@gated-at.bofh.it> <tn3YZ-48j-3@gated-at.bofh.it> <tn4V5-4Nu-59@gated-at.bofh.it>
Organization linux.* mail to news gateway

Show all headers | View raw

On Mon, Mar 20, 2017 at 01:35:12PM +0100, Rafael J. Wysocki wrote:
> On Monday, March 20, 2017 11:36:45 AM Peter Zijlstra wrote:
> > On Sun, Mar 19, 2017 at 02:34:32PM +0100, Rafael J. Wysocki wrote:
> > > From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> > > 
> > > The PELT metric used by the schedutil governor underestimates the
> > > CPU utilization in some cases.  The reason for that may be time spent
> > > in interrupt handlers and similar which is not accounted for by PELT.
> > > 
> > > 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, CPUs that are never idle should
> > > always run at the maximum frequency and make that happen.
> > > 
> > > To that end, add a counter of idle calls to struct sugov_cpu and
> > > modify cpuidle_idle_call() to increment that counter every time it
> > > is about to put the given CPU into an idle state.  Next, make the
> > > schedutil governor look at that counter for the current CPU every
> > > time before it is about to start heavy computations.  If the counter
> > > has not changed for over SUGOV_BUSY_THRESHOLD time (equal to 50 ms),
> > > the CPU has not been idle for at least that long and the governor
> > > will choose the maximum frequency for it without looking at the PELT
> > > metric at all.
> > 
> > Why the time limit?
> 
> One iteration appeared to be a bit too aggressive, but honestly I think
> I need to check again if this thing is regarded as viable at all.
> 

I don't hate the idea; if we don't hit idle; we shouldn't shift down. I
just wonder if we don't already keep a idle-seqcount somewhere; NOHZ and
RCU come to mind as things that might already use something like that.

Back to linux.kernel | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

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

csiph-web