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

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Message-ID: <30cdecf9-703a-eb2b-7c2b-f1e21c805add@st.com>
Date:   Wed, 29 Apr 2020 15:57:21 +0000
From:   Benjamin GAIGNARD <benjamin.gaignard@...com>
To:     "Rafael J. Wysocki" <rjw@...ysocki.net>
CC:     "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>,
        Patrick Bellasi <patrick.bellasi@....com>
Subject: Re: [RFC 0/3] Introduce cpufreq minimum load QoS



On 4/29/20 5:50 PM, Rafael J. Wysocki wrote:
> On Friday, April 24, 2020 1:40:55 PM CEST Benjamin Gaignard wrote:
>> When start streaming from the sensor the CPU load could remain very low
>> because almost all the capture pipeline is done in hardware (i.e. without
>> using the CPU) and let believe to cpufreq governor that it could use lower
>> frequencies. If the governor decides to use a too low frequency that
>> becomes a problem when we need to acknowledge the interrupt during the
>> blanking time.
>> The delay to ack the interrupt and perform all the other actions before
>> the next frame is very short and doesn't allow to the cpufreq governor to
>> provide the required burst of power. That led to drop the half of the frames.
>>
>> To avoid this problem, DCMI driver informs the cpufreq governors by adding
>> a cpufreq minimum load QoS resquest.
> This seems to be addressing a use case that can be addressed with the help of
> utilization clamps with less power overhead.
Do mean clamping the policy frequencies ? I may have miss the API to do 
that...
>
> Thanks!
>
>
>