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Re: [PATCH v2 02/10] cpufreq: provide data for frequency-invariant load-tracking support

From Sudeep Holla <sudeep.holla@arm.com>
Newsgroups linux.kernel
Subject Re: [PATCH v2 02/10] cpufreq: provide data for frequency-invariant load-tracking support
Date 2017-07-13 15:00 +0200
Message-ID <u2LSP-5Kp-31@gated-at.bofh.it> (permalink)
References (5 earlier) <u1WwW-74G-17@gated-at.bofh.it> <u24Xw-3TD-27@gated-at.bofh.it> <u2h8m-39O-23@gated-at.bofh.it> <u2llE-5Pi-17@gated-at.bofh.it> <u2m81-6pg-11@gated-at.bofh.it>
Organization ARM

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On 12/07/17 10:27, Viresh Kumar wrote:
> On 12-07-17, 10:31, Peter Zijlstra wrote:
>> So the problem with the thread is two-fold; one the one hand we like the
>> scheduler to directly set frequency, but then we need to schedule a task
>> to change the frequency, which will change the frequency and around we
>> go.
>>
>> On the other hand, there's very nasty issues with PI. This thread would
>> have very high priority (otherwise the SCHED_DEADLINE stuff won't work)
>> but that then means this thread needs to boost the owner of the i2c
>> mutex. And that then creates a massive bandwidth accounting hole.
>>
>>
>> The advantage of using an interrupt driven state machine is that all
>> those issues go away.
>>
>> But yes, whichever way around you turn things, its crap. But given the
>> hardware its the best we can do.
> 
> Thanks for the explanation Peter.
> 
> IIUC, it will take more time to change the frequency eventually with
> the interrupt-driven state machine as there may be multiple bottom
> halves involved here, for supply, clk, etc, which would run at normal
> priorities now. And those were boosted currently due to the high
> priority sugov thread. And we are fine with that (from performance
> point of view) ?
> 
> Coming back to where we started from (where should we call
> arch_set_freq_scale() from ?).
> 
> I think we would still need some kind of synchronization between
> cpufreq core and the cpufreq drivers to make sure we don't start
> another freq change before the previous one is complete. Otherwise
> the cpufreq drivers would be required to have similar support with
> proper locking in place.
> 

Good point, but with firmware interface we are considering fro
fast-switch, the firmware can override the previous request if it's not
yet started. So I assume that's fine and expected ?

> And if the core is going to get notified about successful freq changes
> (which it should IMHO),

Is that mandatory for even fast-switching ?

-- 
Regards,
Sudeep

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[PATCH v2 00/10] arm, arm64: frequency- and cpu-invariant accounting support for task scheduler Dietmar Eggemann <dietmar.eggemann@arm.com> - 2017-07-06 12:00 +0200
  [PATCH v2 08/10] arm64: wire frequency-invariant accounting support up to the task scheduler Dietmar Eggemann <dietmar.eggemann@arm.com> - 2017-07-06 12:00 +0200
    Re: [PATCH v2 08/10] arm64: wire frequency-invariant accounting  support up to the task scheduler Viresh Kumar <viresh.kumar@linaro.org> - 2017-07-06 12:50 +0200
  [PATCH v2 03/10] drivers base/arch_topology: frequency-invariant load-tracking support Dietmar Eggemann <dietmar.eggemann@arm.com> - 2017-07-06 12:00 +0200
    Re: [PATCH v2 03/10] drivers base/arch_topology: frequency-invariant  load-tracking support Viresh Kumar <viresh.kumar@linaro.org> - 2017-07-06 12:50 +0200
      Re: [PATCH v2 03/10] drivers base/arch_topology: frequency-invariant  load-tracking support Dietmar Eggemann <dietmar.eggemann@arm.com> - 2017-07-07 19:00 +0200
  [PATCH v2 05/10] arm: wire frequency-invariant accounting support up to the task scheduler Dietmar Eggemann <dietmar.eggemann@arm.com> - 2017-07-06 12:00 +0200
    Re: [PATCH v2 05/10] arm: wire frequency-invariant accounting  support up to the task scheduler Viresh Kumar <viresh.kumar@linaro.org> - 2017-07-06 12:50 +0200
  [PATCH v2 02/10] cpufreq: provide data for frequency-invariant load-tracking support Dietmar Eggemann <dietmar.eggemann@arm.com> - 2017-07-06 12:00 +0200
    Re: [PATCH v2 02/10] cpufreq: provide data for frequency-invariant  load-tracking support Viresh Kumar <viresh.kumar@linaro.org> - 2017-07-06 12:50 +0200
      Re: [PATCH v2 02/10] cpufreq: provide data for frequency-invariant load-tracking support "Rafael J. Wysocki" <rjw@rjwysocki.net> - 2017-07-07 00:50 +0200
      Re: [PATCH v2 02/10] cpufreq: provide data for frequency-invariant  load-tracking support Dietmar Eggemann <dietmar.eggemann@arm.com> - 2017-07-07 18:10 +0200
        Re: [PATCH v2 02/10] cpufreq: provide data for frequency-invariant  load-tracking support "Rafael J. Wysocki" <rafael@kernel.org> - 2017-07-07 18:20 +0200
          Re: [PATCH v2 02/10] cpufreq: provide data for frequency-invariant  load-tracking support Dietmar Eggemann <dietmar.eggemann@arm.com> - 2017-07-07 19:10 +0200
            Re: [PATCH v2 02/10] cpufreq: provide data for frequency-invariant load-tracking support "Rafael J. Wysocki" <rjw@rjwysocki.net> - 2017-07-08 14:20 +0200
              Re: [PATCH v2 02/10] cpufreq: provide data for frequency-invariant  load-tracking support Viresh Kumar <viresh.kumar@linaro.org> - 2017-07-10 09:00 +0200
                Re: [PATCH v2 02/10] cpufreq: provide data for frequency-invariant load-tracking support "Rafael J. Wysocki" <rjw@rjwysocki.net> - 2017-07-10 15:00 +0200
                Re: [PATCH v2 02/10] cpufreq: provide data for frequency-invariant  load-tracking support Viresh Kumar <viresh.kumar@linaro.org> - 2017-07-11 08:50 +0200
                Re: [PATCH v2 02/10] cpufreq: provide data for frequency-invariant  load-tracking support Dietmar Eggemann <dietmar.eggemann@arm.com> - 2017-07-11 17:30 +0200
                Re: [PATCH v2 02/10] cpufreq: provide data for frequency-invariant  load-tracking support Sudeep Holla <sudeep.holla@arm.com> - 2017-07-13 14:50 +0200
                Re: [PATCH v2 02/10] cpufreq: provide data for frequency-invariant  load-tracking support Dietmar Eggemann <dietmar.eggemann@arm.com> - 2017-07-13 15:10 +0200
                Re: [PATCH v2 02/10] cpufreq: provide data for frequency-invariant  load-tracking support Sudeep Holla <sudeep.holla@arm.com> - 2017-07-13 16:10 +0200
              Re: [PATCH v2 02/10] cpufreq: provide data for frequency-invariant  load-tracking support Peter Zijlstra <peterz@infradead.org> - 2017-07-10 11:40 +0200
                Re: [PATCH v2 02/10] cpufreq: provide data for frequency-invariant  load-tracking support Viresh Kumar <viresh.kumar@linaro.org> - 2017-07-10 11:50 +0200
                Re: [PATCH v2 02/10] cpufreq: provide data for frequency-invariant  load-tracking support Dietmar Eggemann <dietmar.eggemann@arm.com> - 2017-07-10 12:40 +0200
              Re: [PATCH v2 02/10] cpufreq: provide data for frequency-invariant  load-tracking support Dietmar Eggemann <dietmar.eggemann@arm.com> - 2017-07-10 14:10 +0200
                Re: [PATCH v2 02/10] cpufreq: provide data for frequency-invariant  load-tracking support Viresh Kumar <viresh.kumar@linaro.org> - 2017-07-11 08:10 +0200
                Re: [PATCH v2 02/10] cpufreq: provide data for frequency-invariant  load-tracking support Dietmar Eggemann <dietmar.eggemann@arm.com> - 2017-07-11 17:10 +0200
                Re: [PATCH v2 02/10] cpufreq: provide data for frequency-invariant load-tracking support "Rafael J. Wysocki" <rjw@rjwysocki.net> - 2017-07-11 17:10 +0200
                Re: [PATCH v2 02/10] cpufreq: provide data for frequency-invariant  load-tracking support Dietmar Eggemann <dietmar.eggemann@arm.com> - 2017-07-11 17:20 +0200
                Re: [PATCH v2 02/10] cpufreq: provide data for frequency-invariant  load-tracking support Viresh Kumar <viresh.kumar@linaro.org> - 2017-07-12 06:10 +0200
                Re: [PATCH v2 02/10] cpufreq: provide data for frequency-invariant  load-tracking support Peter Zijlstra <peterz@infradead.org> - 2017-07-12 10:40 +0200
                Re: [PATCH v2 02/10] cpufreq: provide data for frequency-invariant  load-tracking support Viresh Kumar <viresh.kumar@linaro.org> - 2017-07-12 11:30 +0200
                Re: [PATCH v2 02/10] cpufreq: provide data for frequency-invariant  load-tracking support Peter Zijlstra <peterz@infradead.org> - 2017-07-12 13:20 +0200
                Re: [PATCH v2 02/10] cpufreq: provide data for frequency-invariant load-tracking support "Rafael J. Wysocki" <rjw@rjwysocki.net> - 2017-07-13 01:30 +0200
                Re: [PATCH v2 02/10] cpufreq: provide data for frequency-invariant  load-tracking support Peter Zijlstra <peterz@infradead.org> - 2017-07-13 10:00 +0200
                Re: [PATCH v2 02/10] cpufreq: provide data for frequency-invariant  load-tracking support Viresh Kumar <viresh.kumar@linaro.org> - 2017-07-13 10:50 +0200
                Re: [PATCH v2 02/10] cpufreq: provide data for frequency-invariant  load-tracking support Peter Zijlstra <peterz@infradead.org> - 2017-07-13 13:20 +0200
                Re: [PATCH v2 02/10] cpufreq: provide data for frequency-invariant  load-tracking support Sudeep Holla <sudeep.holla@arm.com> - 2017-07-13 16:10 +0200
                Re: [PATCH v2 02/10] cpufreq: provide data for frequency-invariant  load-tracking support Peter Zijlstra <peterz@infradead.org> - 2017-07-13 16:50 +0200
                Re: [PATCH v2 02/10] cpufreq: provide data for frequency-invariant  load-tracking support Sudeep Holla <sudeep.holla@arm.com> - 2017-07-13 17:10 +0200
                Re: [PATCH v2 02/10] cpufreq: provide data for frequency-invariant  load-tracking support Sudeep Holla <sudeep.holla@arm.com> - 2017-07-13 15:00 +0200
                Re: [PATCH v2 02/10] cpufreq: provide data for frequency-invariant  load-tracking support Sudeep Holla <sudeep.holla@arm.com> - 2017-07-13 14:50 +0200
        Re: [PATCH v2 02/10] cpufreq: provide data for frequency-invariant  load-tracking support Viresh Kumar <viresh.kumar@linaro.org> - 2017-07-10 08:50 +0200
  [PATCH v2 04/10] arm: wire cpufreq input data for frequency-invariant accounting up to the arch Dietmar Eggemann <dietmar.eggemann@arm.com> - 2017-07-06 12:00 +0200
    Re: [PATCH v2 04/10] arm: wire cpufreq input data for  frequency-invariant accounting up to the arch Viresh Kumar <viresh.kumar@linaro.org> - 2017-07-06 12:50 +0200
      Re: [PATCH v2 04/10] arm: wire cpufreq input data for  frequency-invariant accounting up to the arch Dietmar Eggemann <dietmar.eggemann@arm.com> - 2017-07-10 17:20 +0200
        Re: [PATCH v2 04/10] arm: wire cpufreq input data for  frequency-invariant accounting up to the arch Viresh Kumar <viresh.kumar@linaro.org> - 2017-07-11 08:40 +0200
  [PATCH v2 09/10] arm64: wire cpu-invariant accounting support up to the task scheduler Dietmar Eggemann <dietmar.eggemann@arm.com> - 2017-07-06 12:00 +0200
    Re: [PATCH v2 09/10] arm64: wire cpu-invariant accounting support up  to the task scheduler Viresh Kumar <viresh.kumar@linaro.org> - 2017-07-06 12:50 +0200
  [PATCH v2 06/10] arm: wire cpu-invariant accounting support up to the task scheduler Dietmar Eggemann <dietmar.eggemann@arm.com> - 2017-07-06 12:00 +0200
    Re: [PATCH v2 06/10] arm: wire cpu-invariant accounting support up  to the task scheduler Viresh Kumar <viresh.kumar@linaro.org> - 2017-07-06 12:50 +0200
  [PATCH v2 01/10] drivers base/arch_topology: free cpumask cpus_to_visit Dietmar Eggemann <dietmar.eggemann@arm.com> - 2017-07-06 12:00 +0200
    Re: [PATCH v2 01/10] drivers base/arch_topology: free cpumask  cpus_to_visit Viresh Kumar <viresh.kumar@linaro.org> - 2017-07-06 12:30 +0200
      Re: [PATCH v2 01/10] drivers base/arch_topology: free cpumask  cpus_to_visit Juri Lelli <juri.lelli@arm.com> - 2017-07-06 13:00 +0200
        Re: [PATCH v2 01/10] drivers base/arch_topology: free cpumask  cpus_to_visit Viresh Kumar <viresh.kumar@linaro.org> - 2017-07-06 13:20 +0200
          Re: [PATCH v2 01/10] drivers base/arch_topology: free cpumask  cpus_to_visit Dietmar Eggemann <dietmar.eggemann@arm.com> - 2017-07-07 18:00 +0200
  [PATCH v2 10/10] drivers base/arch_topology: inline cpu- and frequency-invariant accounting Dietmar Eggemann <dietmar.eggemann@arm.com> - 2017-07-06 12:00 +0200
    Re: [PATCH v2 10/10] drivers base/arch_topology: inline cpu- and  frequency-invariant accounting Viresh Kumar <viresh.kumar@linaro.org> - 2017-07-06 13:00 +0200
      Re: [PATCH v2 10/10] drivers base/arch_topology: inline cpu- and  frequency-invariant accounting Dietmar Eggemann <dietmar.eggemann@arm.com> - 2017-07-10 17:20 +0200

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