linux-kernel - Re: [PATCH V3 1/2] topology: Allow multiple entities to provide sched_freq

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Date:   Wed, 17 Feb 2021 17:10:27 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Ionela Voinescu <ionela.voinescu@....com>
Cc:     Rafael Wysocki <rjw@...ysocki.net>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-pm@...r.kernel.org, Sudeep Holla <sudeep.holla@....com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH V3 1/2] topology: Allow multiple entities to provide
 sched_freq_tick() callback

On 17-02-21, 11:30, Ionela Voinescu wrote:
> The problem is not topology_scale_freq_invariant() but whether a scale
> factor is set for some CPUs.
> 
> Scenario (test system above):
>  - "AMUs" are only supported for [1-2],
>  - cpufreq_supports_freq_invariance() -> false
> 
> What should happen:
>  - topology_scale_freq_invariant() -> false (passed)
>  - all CPUs should have their freq_scale unmodified (1024) - (failed)
>    because only 2 out of 6 CPUs have a method of setting a scale factor
> 
> What does happen:
>  - arch_set_freq_tick() -> topology_set_freq_tick() will set a scale
>    factor for [1-2] based on AMUs. This should not happen. We will end
>    up with invariant signals for bigs and signals that are not freq
>    invariant for littles.

Another case. cpufreq is included as a module and AMU is implemented
partially.

- first time cpufreq driver is inserted, we set up everything and
  freq_scale gets updated on ticks.

- remove cpufreq driver, we are back in same situation.

We can't control it that way.. Or we add another call layer in middle
before the tick-handler gets called for AMU, which will check if we
are fully invariant or not ?

-- 
viresh