linux-kernel - Re: [PATCH v2] schedutil: Allow cpufreq requests to be made even when kthread kicked

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Date:   Wed, 23 May 2018 14:31:01 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Joel Fernandes <joel@...lfernandes.org>
Cc:     "Joel Fernandes (Google.)" <joelaf@...gle.com>,
        linux-kernel@...r.kernel.org,
        "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Patrick Bellasi <patrick.bellasi@....com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Luca Abeni <luca.abeni@...tannapisa.it>,
        Todd Kjos <tkjos@...gle.com>, claudio@...dence.eu.com,
        kernel-team@...roid.com, linux-pm@...r.kernel.org
Subject: Re: [PATCH v2] schedutil: Allow cpufreq requests to be made even
 when kthread kicked

On 22-05-18, 15:09, Joel Fernandes wrote:
> I agree with the race you describe for single policy slow-switch. Good find :)
> 
> The mainline sugov_work could also do such reordering in sugov_work, I think. Even
> with the mutex_unlock in mainline's sugov_work, that work_in_progress write could
> be reordered by the CPU to happen before the read of next_freq. AIUI,
> mutex_unlock is expected to be only a release-barrier.
> 
> Although to be safe, I could just put an smp_mb() there. I believe with that,
> no locking would be needed for such case.
> 
> I'll send out a v3 with Acks for the original patch, and the send out the
> smp_mb() as a separate patch if that's Ok.

Maybe it would be better to get the fix (with smp_mb) first and then
this optimization patch on the top? That would mean that the fix can
get applied to stable kernels easily.

-- 
viresh