linux-kernel - Re: [PATCH 0/3] drivers: Frequency constraint infrastructure

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Date:   Thu, 17 Jan 2019 14:16:31 +0100
From:   Juri Lelli <juri.lelli@...il.com>
To:     "Rafael J. Wysocki" <rafael@...nel.org>
Cc:     Viresh Kumar <viresh.kumar@...aro.org>,
        Rafael Wysocki <rjw@...ysocki.net>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Viresh Kumar <vireshk@...nel.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Matthias Kaehlcke <mka@...omium.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/3] drivers: Frequency constraint infrastructure

On 11/01/19 10:47, Rafael J. Wysocki wrote:
> On Fri, Jan 11, 2019 at 10:18 AM Viresh Kumar <viresh.kumar@...aro.org> wrote:
> >
> > Hi,
> >
> > This commit introduces the frequency constraint infrastructure, which
> > provides a generic interface for parts of the kernel to constraint the
> > working frequency range of a device.
> >
> > The primary users of this are the cpufreq and devfreq frameworks. The
> > cpufreq framework already implements such constraints with help of
> > notifier chains (for thermal and other constraints) and some local code
> > (for user-space constraints). The devfreq framework developers have also
> > shown interest [1] in such a framework, which may use it at a later
> > point of time.
> >
> > The idea here is to provide a generic interface and get rid of the
> > notifier based mechanism.
> >
> > Only one constraint is added for now for the cpufreq framework and the
> > rest will follow after this stuff is merged.
> >
> > Matthias Kaehlcke was involved in the preparation of the first draft of
> > this work and so I have added him as Co-author to the first patch.
> > Thanks Matthias.
> >
> > FWIW, This doesn't have anything to do with the boot-constraints
> > framework [2] I was trying to upstream earlier :)
> 
> This is quite a bit of code to review, so it will take some time.
> 
> One immediate observation is that it seems to do quite a bit of what
> is done in the PM QoS framework, so maybe there is an opportunity for
> some consolidation in there.

Right, had the same impression. :-)

I was also wondering how this new framework is dealing with
constraints/request imposed/generated by the scheduler and related
interfaces (thinking about schedutil and Patrick's util_clamp).

Thanks,

- Juri