linux-kernel - Re: [PATCH v2 -tip] x86/percpu: Use C for arch_raw_cpu

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Message-ID: <CAHk-=wj0UTj3dfuKK=DEQ+AQ2GPUddjVUVZ_nRHdY=L_rRb2KQ@mail.gmail.com>
Date:   Thu, 19 Oct 2023 11:49:37 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Uros Bizjak <ubizjak@...il.com>
Cc:     peterz@...radead.org, Nadav Amit <namit@...are.com>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Andy Lutomirski <luto@...nel.org>,
        Brian Gerst <brgerst@...il.com>,
        Denys Vlasenko <dvlasenk@...hat.com>,
        "H . Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>
Subject: Re: [PATCH v2 -tip] x86/percpu: Use C for arch_raw_cpu_ptr()

On Thu, 19 Oct 2023 at 11:16, Uros Bizjak <ubizjak@...il.com> wrote:
>
> And NO (whee...), there is no rematerialization of asm (foo() ). OTOH,
> there is also no rematerialization from non-volatile memory (bar() ),
> although it would be more optimal than spill to/fill from a frame pair
> of moves. I wonder what are "certain circumstances" that the
> documentation is referring to.

Honestly, I've actually never seen gcc rematerialize anything at all.

I really only started worrying about remat issues in a theoretical
sense, and because I feel it would be relatively *easy* to do for
something where the source is a load.

              Linus