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From:   Vincent Guittot <vincent.guittot@linaro.org>
Date:   Wed, 29 Apr 2020 19:08:14 +0200
Message-ID: <CAKfTPtBNH8x=83RVQajgK859qQGjMTyvEdP4GioMONEZp9t-NA@mail.gmail.com>
Subject: Re: [RFC 0/3] Introduce cpufreq minimum load QoS
To:     "Rafael J. Wysocki" <rjw@rjwysocki.net>
Cc:     Benjamin Gaignard <benjamin.gaignard@st.com>,
        Viresh Kumar <viresh.kumar@linaro.org>, hugues.fruchet@st.com,
        mchehab@kernel.org, Maxime Coquelin <mcoquelin.stm32@gmail.com>,
        Alexandre TORGUE <alexandre.torgue@st.com>,
        Pavel Machek <pavel@ucw.cz>, Len Brown <len.brown@intel.com>,
        "open list:THERMAL" <linux-pm@vger.kernel.org>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        linux-media@vger.kernel.org,
        linux-stm32@st-md-mailman.stormreply.com,
        LAK <linux-arm-kernel@lists.infradead.org>,
        Patrick Bellasi <patrick.bellasi@arm.com>
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On Wed, 29 Apr 2020 at 17:50, Rafael J. Wysocki <rjw@rjwysocki.net> 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.

Can't freq_qos_update_request() be also used if you don't have cgroup
enabled on your system ?

>
> Thanks!
>
>
>