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

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Message-ID: <20180522102305.uxph4u4o2zrvu4tx@vireshk-i7>
Date:   Tue, 22 May 2018 15:53:05 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Joel Fernandes <joel@...lfernandes.org>
Cc:     Patrick Bellasi <patrick.bellasi@....com>,
        "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>,
        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 21-05-18, 10:20, Joel Fernandes wrote:
> On Mon, May 21, 2018 at 06:00:50PM +0100, Patrick Bellasi wrote:
> > If that's the case, this means that if, for example, during a
> > frequency switch you get a request to reduce the frequency (e.g.
> > deadline task passing the 0-lag time) and right after a request to
> > increase the frequency (e.g. the current FAIR task tick)... you will
> > enqueue a freq drop followed by a freq increase and actually do two
> > frequency hops?

I don't think so.

Consider the kthread as running currently and has just cleared the
work_in_progress flag. Sched update comes at that time and we decide
to reduce the frequency, we queue another work and update next_freq.
Now if another sched update comes before the kthread finishes its
previous loop, we will simply update next_freq and return. So when the
next time kthread runs, it will pick the most recent update.

Where is the problem both of you see ?

-- 
viresh