linux-kernel - Re: x86 copy performance regression

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Message-ID: <CAHk-=wibWdTp-kdCKc-F3d4aVcHO40qqoxoATG+KhVivYE0TqA@mail.gmail.com>
Date:   Fri, 26 May 2023 13:37:15 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Eric Dumazet <edumazet@...gle.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        netdev <netdev@...r.kernel.org>
Subject: Re: x86 copy performance regression

On Fri, May 26, 2023 at 11:33 AM Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
>
> Anyway, I guess *this* avoids all issues. It creates an extra jump to
> a jump for the case where the CPU doesn't have ERMS, but I guess we
> don't really care about those CPUs anyway.

Well, I'm obviously wrong, because my very own CPU (AMD Zen 2) doesn't do ERMS.

But the extra 'jmp' doesn't seem to appreciably matter, so I guess I
don't care. It does show up in profiles, but only barely.

I've committed and pushed out the fix.

               Linus