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

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Message-ID: <7657495.QyJl4BcWH5@kreacher>
Date:   Wed, 29 Apr 2020 17:50:04 +0200
From:   "Rafael J. Wysocki" <rjw@...ysocki.net>
To:     Benjamin Gaignard <benjamin.gaignard@...com>
Cc:     viresh.kumar@...aro.org, hugues.fruchet@...com, mchehab@...nel.org,
        mcoquelin.stm32@...il.com, alexandre.torgue@...com, pavel@....cz,
        len.brown@...el.com, linux-pm@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-media@...r.kernel.org,
        linux-stm32@...md-mailman.stormreply.com,
        linux-arm-kernel@...ts.infradead.org,
        Patrick Bellasi <patrick.bellasi@....com>
Subject: Re: [RFC 0/3] Introduce cpufreq minimum load QoS

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.

Thanks!