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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Tue, 7 Mar 2023 13:14:29 -0800
Message-ID: <CAHk-=whzzd53rW5Uk0oK7bXVXS_X6sJiisnhrqaz+MkutO7qug@mail.gmail.com>
Subject: Re: [PATCH] x86/resctrl: avoid compiler optimization in __resctrl_sched_in
To:     "Luck, Tony" <tony.luck@intel.com>
Cc:     Jakub Jelinek <jakub@redhat.com>,
        Segher Boessenkool <segher@kernel.crashing.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Nick Desaulniers <ndesaulniers@google.com>,
        "Eranian, Stephane" <eranian@google.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "Chatre, Reinette" <reinette.chatre@intel.com>,
        "Yu, Fenghua" <fenghua.yu@intel.com>,
        "peternewman@google.com" <peternewman@google.com>,
        "james.morse@arm.com" <james.morse@arm.com>,
        "babu.moger@amd.com" <babu.moger@amd.com>,
        "ananth.narayan@amd.com" <ananth.narayan@amd.com>,
        "vschneid@redhat.com" <vschneid@redhat.com>,
        Nathan Chancellor <nathan@kernel.org>,
        clang-built-linux <llvm@lists.linux.dev>,
        Borislav Petkov <bp@alien8.de>,
        "H. Peter Anvin" <hpa@zytor.com>,
        "linux-toolchains@vger.kernel.org" <linux-toolchains@vger.kernel.org>
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On Tue, Mar 7, 2023 at 1:11=E2=80=AFPM Luck, Tony <tony.luck@intel.com> wro=
te:
>
> Can you expand about part "a" ... Linux has zillions of static inline fun=
ctions
> in header files to handle CONFIG options. One version is the real McCoy
> while the other is just a stub for the CONFIG=3Dn case.
>
> What's different about this one?

See the patch I just sent out.

Linux has a lot of "static inline" functions. But that's not at all
what that function was. It was literally just

  static void __resctrl_sched_in(..)

which is disgusting and very wrong.

I hope that compilers then just ignored it ("It's static and not used,
so I'm not generating that code"), and that header file isn't included
in very many places, but it's still very wrong.

               Linus