linux-kernel - Re: [PATCH] x86/resctrl: avoid compiler optimization in __resctrl_sched

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Date:   Tue, 7 Mar 2023 13:19:05 -0800
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     "Luck, Tony" <tony.luck@...el.com>,
        Jakub Jelinek <jakub@...hat.com>,
        Segher Boessenkool <segher@...nel.crashing.org>,
        Peter Zijlstra <peterz@...radead.org>,
        "Eranian, Stephane" <eranian@...gle.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Chatre, Reinette" <reinette.chatre@...el.com>,
        "Yu, Fenghua" <fenghua.yu@...el.com>,
        "peternewman@...gle.com" <peternewman@...gle.com>,
        "james.morse@....com" <james.morse@....com>,
        "babu.moger@....com" <babu.moger@....com>,
        "ananth.narayan@....com" <ananth.narayan@....com>,
        "vschneid@...hat.com" <vschneid@...hat.com>,
        Nathan Chancellor <nathan@...nel.org>,
        clang-built-linux <llvm@...ts.linux.dev>,
        Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        "linux-toolchains@...r.kernel.org" <linux-toolchains@...r.kernel.org>
Subject: Re: [PATCH] x86/resctrl: avoid compiler optimization in __resctrl_sched_in

On Tue, Mar 7, 2023 at 1:16 PM Nick Desaulniers <ndesaulniers@...gle.com> wrote:
>
> >
> > Can you expand about part "a" ... Linux has zillions of static inline functions
> > in header files to handle CONFIG options. One version is the real McCoy
> > while the other is just a stub for the CONFIG=n case.
>
> Right, I had the same question.
>
> Perhaps it's more so that no one calls __resctrl_sched_in, only
> resctrl_sched_in, therefor they should be folded into one function?

If you think it should be inlined, it should be marked as such.

And if you *don't* think it should be inlined - quite possibly the
right answer here - the definition of that function damn well
shouldn't be in a header file.

So either way, that __resctrl_sched_in() was wrong, wrong, wrong.

           Linus