linux-kernel - Re: [PATCH] sched/cpufreq: Align trace event behavior of fast switching

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Date:   Thu, 8 Aug 2019 17:18:00 +0100
From:   Douglas Raillard <douglas.raillard@....com>
To:     "Rafael J. Wysocki" <rafael@...nel.org>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH] sched/cpufreq: Align trace event behavior of fast
 switching

Hi Rafael,

On 8/7/19 9:40 PM, Rafael J. Wysocki wrote:
> On Wed, Aug 7, 2019 at 5:34 PM Douglas RAILLARD
> <douglas.raillard@....com> wrote:
>>
>> Fast switching path only emits an event for the CPU of interest, whereas the
>> regular path emits an event for all the CPUs that had their frequency changed,
>> i.e. all the CPUs sharing the same policy.
>>
>> With the current behavior, looking at cpu_frequency event for a given CPU that
>> is using the fast switching path will not give the correct frequency signal.
> 
> Do you actually have any systems where that is a problem?  If so, then
> what are they?
> 

That happens on Google Pixel 3 smartphone, which uses this cpufreq driver: drivers/cpufreq/qcom-cpufreq-hw.c.

[1] git clone https://git.linaro.org/people/amit.pundir/linux.git -b blueline-mainline-tracking

Thanks,
Douglas