linux-kernel - Re: [PATCH v2 4/4] x86/percpu: Use C for percpu read/write accessors

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Message-ID: <CAHk-=whKc9UCsrZ6sNRb=T2Yhy4Dhr=LUBi9r-gPhfwCmuOeZA@mail.gmail.com>
Date:   Wed, 4 Oct 2023 13:12:40 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Uros Bizjak <ubizjak@...il.com>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org,
        Andy Lutomirski <luto@...nel.org>,
        Ingo Molnar <mingo@...nel.org>, Nadav Amit <namit@...are.com>,
        Brian Gerst <brgerst@...il.com>,
        Denys Vlasenko <dvlasenk@...hat.com>,
        "H . Peter Anvin" <hpa@...or.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...en8.de>,
        Josh Poimboeuf <jpoimboe@...hat.com>
Subject: Re: [PATCH v2 4/4] x86/percpu: Use C for percpu read/write accessors

On Wed, 4 Oct 2023 at 13:08, Uros Bizjak <ubizjak@...il.com> wrote:
>
> You get a store forwarding stall when you write a bigger operand to
> memory and then read part of it, if the smaller part doesn't start at
> the same address.

I don't think that has been true for over a decade now.

Afaik, any half-way modern Intel and AMD cores will forward any fully
contained load.

The whole "same address" was a P4 thing, iirc.

          Linus