linux-kernel - Re: [PATCH 2/2] x86, sched: Fix the undefined reference building error of init_freq_invariance

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Date:   Thu, 6 Jan 2022 17:49:46 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Borislav Petkov <bp@...en8.de>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        Huang Rui <ray.huang@....com>,
        "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Yuan, Perry" <Perry.Yuan@....com>,
        "Su, Jinzhou (Joe)" <Jinzhou.Su@....com>,
        "Du, Xiaojian" <Xiaojian.Du@....com>,
        kernel test robot <lkp@...el.com>,
        Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        "x86@...nel.org" <x86@...nel.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>
Subject: Re: [PATCH 2/2] x86, sched: Fix the undefined reference building
 error of init_freq_invariance_cppc

On Thu, Jan 6, 2022 at 5:23 PM Borislav Petkov <bp@...en8.de> wrote:
>
> On Thu, Jan 06, 2022 at 05:12:51PM +0100, Rafael J. Wysocki wrote:
> > And why can't it be a real use case?
>
> You mean there's someone out there running SMP=n kernels on current
> hardware which has CPPC too? Yeah, right.
>
> > The honest answer is that we don't know.
> >
> > Moreover, AFAICS the requisite #ifdeffery is there already and  the
> > problem is that the init_freq_invariance_cppc() defined in smpboot.c
> > is not exported to modules and the CPPC code is modular in this build.
>
> Yah, I saw that. And that's why I'm saying CPPC should depend on SMP -
> because it needs that functionality which is defined there.

In fact, the CPPC code itself doesn't need that functionality.

The init_freq_invariance_cppc() call is in there, because
amd_set_max_freq_ratio() depends on CPPC and it is pointless to run it
when CPPC is not supported, not the other way around.

> But if you really wanna support SMP=n, I don't care that much to debate
> this more - I just think it is silly.

Well, I just don't want to stop supporting SMP=n just because we can't
possibly get our build dependencies right.