linux-kernel - Re: [PATCH 1/5] x86/percpu: Differentiate this_cpu_{}() and __this_cpu

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Message-ID: <CAHk-=wgfx6rUXpH16A9OAyEEh9nf18pk9mL7Wkz5b6eDc9dPpA@mail.gmail.com>
Date:   Wed, 27 Feb 2019 11:41:31 -0800
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Nadav Amit <namit@...are.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>, Borislav Petkov <bp@...en8.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andrew Lutomirski <luto@...nel.org>,
        Linux List Kernel Mailing <linux-kernel@...r.kernel.org>,
        Matthew Wilcox <willy@...radead.org>
Subject: Re: [PATCH 1/5] x86/percpu: Differentiate this_cpu_{}() and __this_cpu_{}()

On Wed, Feb 27, 2019 at 9:57 AM Nadav Amit <namit@...are.com> wrote:
>
> I’ll have a look at some specific function assembly, but overall, the “+m”
> approach might prevent even more code optimizations than the “volatile” one.

Ok, that being the case, let's forget that patch.

I still wonder about the added volatiles to the xadd/cmpxchg cases,
which already had the "memory" clobber which should make the volatile
immaterial..

                 Linus