linux-kernel - Re: [RFC PATCH] sched/cpufreq/schedutil: handling urgent frequency requests

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Message-ID: <CAJZ5v0hkeCOybZo4LPpwiE0PG8msCWQkgiHJbpi-6zJHtOQbfg@mail.gmail.com>
Date:   Wed, 9 May 2018 10:25:19 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Juri Lelli <juri.lelli@...hat.com>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        Joel Fernandes <joel@...lfernandes.org>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Claudio Scordino <claudio@...dence.eu.com>,
        Linux Kernel Mailing List <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>,
        Luca Abeni <luca.abeni@...tannapisa.it>,
        Joel Fernandes <joelaf@...gle.com>,
        Linux PM <linux-pm@...r.kernel.org>
Subject: Re: [RFC PATCH] sched/cpufreq/schedutil: handling urgent frequency requests

On Wed, May 9, 2018 at 10:23 AM, Juri Lelli <juri.lelli@...hat.com> wrote:
> On 09/05/18 10:05, Rafael J. Wysocki wrote:
>> On Wed, May 9, 2018 at 9:01 AM, Joel Fernandes <joel@...lfernandes.org> wrote:
>> > On Wed, May 09, 2018 at 12:24:49PM +0530, Viresh Kumar wrote:
>> >> On 09-05-18, 08:45, Juri Lelli wrote:
>> >> > On 08/05/18 21:54, Joel Fernandes wrote:
>> >> > Isn't this potentially introducing unneeded irq pressure (and doing the
>> >> > whole wakeup the kthread thing), while the already active kthread could
>> >> > simply handle multiple back-to-back requests before going to sleep?
>> >>
>> >> And then we may need more instances of the work item and need to store
>> >> a different value of next_freq with each work item, as we can't use
>> >> the common one anymore as there would be races around accessing it ?
>> >
>> > Exactly. I think it also doesn't make sense to over write an already
>> > committed request either so better to store them separate (?). After the
>> > "commit", that previous request is done..
>>
>> Why is it?
>>
>> In the non-fast-switch case the "commit" only means queuing up an
>> irq_work.  Which BTW is one of the reasons for having work_in_progress
>> even if your kthread can handle multiple work items in one go.
>>
>> You may try to clear work_in_progress in sugov_irq_work() instead of
>> in sugov_work(), though.
>>
>> BTW, I'm not sure if the comment in sugov_irq_work() still applies.  Juri?
>
> It doesn't anymore. sugov kthreads are now being "ignored". Should have
> remove it with the DL set of changes, sorry about that.

No worries, you can still do that. ;-)