linux-kernel - Re: [PATCH 00/14] Modularize schedutil

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Date:   Tue, 12 May 2020 19:30:52 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Quentin Perret <qperret@...gle.com>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Greg KH <gregkh@...uxfoundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Sudeep Holla <sudeep.holla@....com>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Benjamin Segall <bsegall@...gle.com>,
        Mel Gorman <mgorman@...e.de>,
        "Luis R. Rodriguez" <mcgrof@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Iurii Zaikin <yzaikin@...gle.com>,
        Frederic Weisbecker <fweisbec@...il.com>,
        Todd Kjos <tkjos@...gle.com>,
        "Cc: Android Kernel" <kernel-team@...roid.com>
Subject: Re: [PATCH 00/14] Modularize schedutil

On Tue, May 12, 2020 at 6:26 PM Quentin Perret <qperret@...gle.com> wrote:
>
> On Tuesday 12 May 2020 at 17:30:36 (+0200), Rafael J. Wysocki wrote:
> > On Tue, May 12, 2020 at 5:11 PM Quentin Perret <qperret@...gle.com> wrote:
> > > The end goal with GKI is the following: Google will release a single
> > > binary kernel image (signed, etc etc) that all devices using a given
> > > Android version will be required to use. That image is however going to
> > > be only for the core of the kernel (no drivers or anything of the sort).
> > > Vendors and OEMs, on their end, will be responsible to build and ship
> > > GKI-compatible modules for their respective devices. So, Android devices
> > > will eventually ship with a Google-issued GKI, plus a bunch of
> > > vendor-provided modules loaded during boot.
> >
> > If that is the case, then I absolutely think that schedutil should be
> > part of the GKI.
> >
> > Moreover, that would have been my opinion even if it had been modular
> > in the first place.
>
> I definitely understand the feeling. Heck I contributed to schedutil, so
> I'd love to see the entire world run it :-)
>
> But my personal preference doesn't seem to matter in this world, sadly.
> The truth is, we cannot afford to be arbitrary in our decisions in GKI.
> Switching governors and such is a fully supported feature upstream, and
> it has been for a long time. Taking that away from partners is not the
> goal, nor the intention, of GKI.

It still will be possible with schedutil built-in, however.

> They will be able to choose whatever
> governor they want, because there are no *objective* reasons to not let
> them do that.

Which, again, is still possible with non-modular schedutil AFAICS.

I don't see any technical reason for making schedutil modular in the
context of GKI other than to make the GKI image smaller, but I don't
expect that to be significant enough.

Is there anything else I am missing?

> > > This is a significant shift from the current model where vendors
> > > completely own the kernel, and are largely free to use the kernel config
> > > they want. Today, those who don't use schedutil are free to turn the
> > > config off, for example.
> >
> > So why is this regarded as a good thing?
>
> You mean using something else than schedutil?

I mean why allowing people to compile schedutil out is regarded as a good thing.

> It is not seen as a good
> thing at all, at least not by me. But we have the same problem as
> upstream. We cannot remove the other governors or the governor API for a
> simple reason: they have users :/

I'm not saying about removing any of that.  I'm just trying to
understand why you need schedutil to be modular so as to make those
things possible.

Cheers!