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

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Date:   Fri, 8 May 2020 14:05:07 +0100
From:   Quentin Perret <qperret@...gle.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Greg KH <gregkh@...uxfoundation.org>, linux-kernel@...r.kernel.org,
        linux-pm@...r.kernel.org, tglx@...utronix.de, mingo@...hat.com,
        bp@...en8.de, x86@...nel.org, hpa@...or.com, sudeep.holla@....com,
        rafael@...nel.org, viresh.kumar@...aro.org, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, dietmar.eggemann@....com,
        rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de,
        mcgrof@...nel.org, keescook@...omium.org, yzaikin@...gle.com,
        fweisbec@...il.com, tkjos@...gle.com, kernel-team@...roid.com
Subject: Re: [PATCH 00/14] Modularize schedutil

On Friday 08 May 2020 at 13:31:41 (+0200), Peter Zijlstra wrote:
> On Fri, May 08, 2020 at 12:16:12PM +0100, Quentin Perret wrote:
> > However, the point I tried to make here is orthogonal to that. As of
> > today using another governor than schedutil is fully supported upstream,
> > and in fact it isn't even enabled by default for most archs. If vendors
> > feel like using something else makes their product better, then I don't
> > see why I need to argue with them about that. And frankly I don't see
> > that support being removed from upstream any time soon.
> 
> Right, it'll take a while to get there. But that doesn't mean we
> shouldn't encourage schedutil usage wherever and whenever possible. That
> includes not making it easier to not use it.
> 
> In that respect making it modular goes against our ultimate goal (world
> domination, <mad giggles here>).

Right, I definitely understand the sentiment. OTOH, things like that
give vendors weapons against GKI ('you-force-us-to-build-in-things-we-dont't-want'
etc etc). That _is_ true to some extent, but it's important we make sure
to keep this to an absolute minimum, otherwise GKI just won't happen
(and I really think that'd be a shame, GKI _is_ a good thing for
upstream).

And sure, schedutil isn't that big, and we can make an exception. But
I'm sure you know what happens when you starting making exceptions ;)

So, all in all, I don't think the series actively makes schedutil worse
by adding out-of-line calls in the hot path or anything like that, and
having it as a module helps with GKI which I'm arguing is a good thing
in the grand scheme of things. That of course is only true if we can
agree on a reasonable set of exported symbols, so I'll give others some
time to complain and see if I can post a v2 addressing these issues!

Cheers,
Quentin