linux-kernel - Re: x86 copy performance regression

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Message-ID: <CAHk-=whkci5ck5Him8Lx5ECKHEtj=bipYmOCGe8DWrrp8uDq5g@mail.gmail.com>
Date:   Fri, 26 May 2023 10:00:22 -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 9:56 AM Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
>
> Ahh, I tested it in an allmodconfig build, but only building that one
> file, and not trying to link it. And gas was apparent;y perfectly
> happy just leaving that undefined feature as a relocation.

Oh, never mind. Even with that fixed, objtool is very unhappy about my
hack, because it knows about short jumps, and despite me encoding it
as a sequence of bytes, objtool will just decode it anyway and say
"that's not right".

Grr, I tried so hard to get the exact asm I wanted, but our
sanity-checking catches my cleverness and stops me in my tracks.

Let me go look at it some more. I *really* didn't want to make the
code worse for ERSM.

             Linus