Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
MIME-Version: 1.0
References: <CANn89iKUbyrJ=r2+_kK+sb2ZSSHifFZ7QkPLDpAtkJ8v4WUumA@mail.gmail.com>
 <CAHk-=whqNMUPbjCyMjyxfH_5-Xass=DrMkPT5ZTJbFrtU=qDEQ@mail.gmail.com>
 <CANn89i+bExb_P6A9ROmwqNgGdO5o8wawVZ5r3MHnz0qfhxvTtA@mail.gmail.com>
 <CAHk-=wig6VizZHtRznz7uAWa-hHWjrCNANZ9B+1G=aTWPiVH4g@mail.gmail.com>
 <CAHk-=whkci5ck5Him8Lx5ECKHEtj=bipYmOCGe8DWrrp8uDq5g@mail.gmail.com> <CAHk-=whtDupvWtj_ow11wU4_u=KvifTqno=5mW1VofyehjdVRA@mail.gmail.com>
In-Reply-To: <CAHk-=whtDupvWtj_ow11wU4_u=KvifTqno=5mW1VofyehjdVRA@mail.gmail.com>
From:   Eric Dumazet <edumazet@google.com>
Date:   Fri, 26 May 2023 19:25:23 +0200
Message-ID: <CANn89i+u8jvfSQAQ=_JY0be56deJNhKgDWbqpDAvfm-i34qX9A@mail.gmail.com>
Subject: Re: x86 copy performance regression
To:     Linus Torvalds <torvalds@linux-foundation.org>
Cc:     LKML <linux-kernel@vger.kernel.org>,
        netdev <netdev@vger.kernel.org>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
Precedence: bulk

On Fri, May 26, 2023 at 7:17=E2=80=AFPM Linus Torvalds
<torvalds@linux-foundation.org> wrote:
>
> On Fri, May 26, 2023 at 10:00=E2=80=AFAM Linus Torvalds
> <torvalds@linux-foundation.org> wrote:
> >
> > Let me go look at it some more. I *really* didn't want to make the
> > code worse for ERMS
>
> Oh well. I'll think about it some more in the hope that I can come up
> with something clever that doesn't make objtool hate me, but in the
> meantime let me just give you the "not clever" patch.
>
> It generates an annoying six-byte jump when the small 2-byte one would
> work just fine, but I guess only my pride is wounded.

arch/x86/lib/copy_user_64.S:34:2: error: invalid instruction mnemonic
'alternative'
 alternative "jae .Lunrolled", "jae .Llarge", ( 9*32+ 9)
 ^~~~~~~~~~~

I changed alternative to ALTERNATIVE to let it build.

 SYM_FUNC_START(rep_movs_alternative)
        cmpq $64,%rcx
-       jae .Lunrolled
+       ALTERNATIVE "jae .Lunrolled", "jae .Llarge", X86_FEATURE_ERMS

I will report test result soon, thanks !