Re: [PATCH 00/14] Modularize schedutil

From: Quentin Perret <qperret@google.com>
To: "Rafael J. Wysocki" <rafael@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>,
	Greg KH <gregkh@linuxfoundation.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Linux PM <linux-pm@vger.kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
	the arch/x86 maintainers <x86@kernel.org>,
	"H. Peter Anvin" <hpa@zytor.com>,
	Sudeep Holla <sudeep.holla@arm.com>,
	Viresh Kumar <viresh.kumar@linaro.org>,
	Juri Lelli <juri.lelli@redhat.com>,
	Vincent Guittot <vincent.guittot@linaro.org>,
	Dietmar Eggemann <dietmar.eggemann@arm.com>,
	Steven Rostedt <rostedt@goodmis.org>,
	Benjamin Segall <bsegall@google.com>,
	Mel Gorman <mgorman@suse.de>,
	"Luis R. Rodriguez" <mcgrof@kernel.org>,
	Kees Cook <keescook@chromium.org>,
	Iurii Zaikin <yzaikin@google.com>,
	Frederic Weisbecker <fweisbec@gmail.com>,
	Todd Kjos <tkjos@google.com>,
	"Cc: Android Kernel" <kernel-team@android.com>
Subject: Re: [PATCH 00/14] Modularize schedutil
Date: Tue, 12 May 2020 17:26:30 +0100	[thread overview]
Message-ID: <20200512162630.GC101124@google.com> (raw)
In-Reply-To: <CAJZ5v0inoge=nWQtv-rU_ReQUMZA5w-PZXuSpHHj1UHn-S7aSA@mail.gmail.com>

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

> > 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? 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 :/

Thanks,
Quentin