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 17:12:51 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Borislav Petkov <bp@...en8.de>
Cc:     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 4:55 PM Borislav Petkov <bp@...en8.de> wrote:
>
> On Thu, Jan 06, 2022 at 10:55:20PM +0800, Huang Rui wrote:
> > I just thought the CPPC function should be able to work on single core even
> > SMP is disabled.
>
> Why, because SMP=n is a real use case?!

And why can't it be a real use case?

> FWIW, we were even speculating on removing SMP=n so how practical is
> using CPPC on SMP=n at all?

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.