linux-kernel - Re: [RFC RESEND 0/3] Introduce cpufreq minimum load QoS

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Date:   Wed, 27 May 2020 17:03:52 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Benjamin GAIGNARD <benjamin.gaignard@...com>
Cc:     Vincent Guittot <vincent.guittot@...aro.org>,
        Valentin Schneider <valentin.schneider@....com>,
        "rjw@...ysocki.net" <rjw@...ysocki.net>,
        "viresh.kumar@...aro.org" <viresh.kumar@...aro.org>,
        Hugues FRUCHET <hugues.fruchet@...com>,
        "mchehab@...nel.org" <mchehab@...nel.org>,
        "mcoquelin.stm32@...il.com" <mcoquelin.stm32@...il.com>,
        Alexandre TORGUE <alexandre.torgue@...com>,
        "pavel@....cz" <pavel@....cz>,
        "len.brown@...el.com" <len.brown@...el.com>,
        "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-media@...r.kernel.org" <linux-media@...r.kernel.org>,
        "linux-stm32@...md-mailman.stormreply.com" 
        <linux-stm32@...md-mailman.stormreply.com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [RFC RESEND 0/3] Introduce cpufreq minimum load QoS

On Wed, May 27, 2020 at 4:54 PM Benjamin GAIGNARD
<benjamin.gaignard@...com> wrote:
>
>
>
> On 5/27/20 2:48 PM, Benjamin GAIGNARD wrote:
> >
> >
> > On 5/27/20 2:22 PM, Vincent Guittot wrote:
> >> On Wed, 27 May 2020 at 13:17, Benjamin GAIGNARD
> >> <benjamin.gaignard@...com> wrote:
> >>>
> >>>
> >>> On 5/27/20 12:09 PM, Valentin Schneider wrote:
> >>>> Hi Benjamin,
> >>>>
> >>>> On 26/05/20 16:16, Benjamin Gaignard wrote:
> >>>>> A first round [1] of discussions and suggestions have already be
> >>>>> done on
> >>>>> this series but without found a solution to the problem. I resend
> >>>>> it to
> >>>>> progress on this topic.
> >>>>>
> >>>> Apologies for sleeping on that previous thread.
> >>>>
> >>>> So what had been suggested over there was to use uclamp to boost the
> >>>> frequency of the handling thread; however if you use threaded IRQs you
> >>>> get RT threads, which already get the max frequency by default (at
> >>>> least
> >>>> with schedutil).
> >>>>
> >>>> Does that not work for you, and if so, why?
> >>> That doesn't work because almost everything is done by the hardware
> >>> blocks
> >>> without charge the CPU so the thread isn't running. I have done the
> >>> tests with schedutil
> >>> and ondemand scheduler (which is the one I'm targeting). I have no
> >>> issues when using
> >>> performance scheduler because it always keep the highest frequencies.
> >> IMHO, the only way to ensure a min frequency for anything else than a
> >> thread is to use freq_qos_add_request() just like cpufreq cooling
> >> device but for the opposite QoS. This can be applied only on the
> >> frequency domain of the CPU which handles the interrupt.
> > I will give a try with this idea.
> > Thanks.
>
> Adding freq_qos_add_request(FREQ_QOS_MIN) when starting streaming frames
> solve my problem. I remove the request at the end of the streaming to
> restore
> the default value.

You may as well add the request once at the init time with the request
value set to PM_QOS_MIN_FREQUENCY_DEFAULT_VALUE initially and update
it as needed going forward.