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

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Message-ID: <jhjtv11cabk.mognet@arm.com>
Date:   Thu, 30 Apr 2020 15:33:35 +0100
From:   Valentin Schneider <valentin.schneider@....com>
To:     Benjamin GAIGNARD <benjamin.gaignard@...com>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        "viresh.kumar\@linaro.org" <viresh.kumar@...aro.org>,
        Hugues FRUCHET <hugues.fruchet@...com>,
        "mchehab\@kernel.org" <mchehab@...nel.org>,
        "mcoquelin.stm32\@gmail.com" <mcoquelin.stm32@...il.com>,
        Alexandre TORGUE <alexandre.torgue@...com>,
        "pavel\@ucw.cz" <pavel@....cz>,
        "len.brown\@intel.com" <len.brown@...el.com>,
        "linux-pm\@vger.kernel.org" <linux-pm@...r.kernel.org>,
        "linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-media\@vger.kernel.org" <linux-media@...r.kernel.org>,
        "linux-stm32\@st-md-mailman.stormreply.com" 
        <linux-stm32@...md-mailman.stormreply.com>,
        "linux-arm-kernel\@lists.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        Patrick Bellasi <patrick.bellasi@....com>
Subject: Re: [RFC 0/3] Introduce cpufreq minimum load QoS


On 30/04/20 14:46, Benjamin GAIGNARD wrote:
>> That's not what I meant.
>>
>> I suppose that the interrupt processing in question takes place in
>> process context and so you may set the lower clamp on the utilization
>> of the task carrying that out.
>
> I have try to add this code when starting streaming (before the first
> interrupt) the frames from the sensor:
> const struct sched_attr sched_attr = {
>    .sched_util_min = 10000, /* 100% of usage */

Unless you play with SCHED_CAPACITY_SHIFT, the max should be 1024 -
i.e. SCHED_CAPACITY_SCALE. That's a really big boost, but that's for you to
benchmark.

>    .sched_flags = SCHED_FLAG_UTIL_CLAMP_MIN,
>   };
>
> sched_setattr(current, &sched_attr);
>
> I don't see any benefices maybe there is some configuration flags to set.
>
> How changing sched_util_min could impact cpufreq ondemand governor ?
> Does it change the value returned when the governor check the idle time ?
>

You'll have to use the schedutil governor for uclamp to have an effect. And
arguably that's what you should be using, unless something explicitly
prevents you from doing that.

>>
>> Alternatively, that task may be a deadline one.