netdev - Re: x86 copy performance regression

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Message-ID: <CANn89iJ3=OiZEABRQQLL6z+J-Wy8AvTJz6NPLQDOtzREiiYb4Q@mail.gmail.com>
Date: Fri, 26 May 2023 19:51:22 +0200
From: Eric Dumazet <edumazet@...gle.com>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: LKML <linux-kernel@...r.kernel.org>, netdev <netdev@...r.kernel.org>
Subject: Re: x86 copy performance regression

On Fri, May 26, 2023 at 7:40 PM Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
>
> On Fri, May 26, 2023 at 10:25 AM Eric Dumazet <edumazet@...gle.com> wrote:
> >
> > arch/x86/lib/copy_user_64.S:34:2: error: invalid instruction mnemonic
> > 'alternative'
>
> Ok, that's just odd. For me, assembler mnemonics - very much including
> macros - are case-insensitive.
>
> It's actually documented that way, with the example given is for a
> macro that is declared as "sum" and then used as "SUM":
>
>    https://sourceware.org/binutils/docs/as/Macro.html
>
> And if you want to use macros as pseudo-instructions, that's what you
> want, since typically assembler instructions are not case sensitive.
>
> But yeah, your build environment is clearly different, and yes, we
> declare the macro with all caps, and other places use it that way too.
>
> Clang?

Yes, we use clang here ...

Hmmm

[   25.532236] RIP: 0010:0xffffffffa5a85134
[   25.536173] Code: Unable to access opcode bytes at 0xffffffffa5a8510a.
[   25.542720] RSP: 0000:ffff92f08159bcd8 EFLAGS: 00050206
[   25.547960] RAX: 00007ffc3b16c318 RBX: 0000000000000000 RCX: 0000000000000170
[   25.555118] RDX: 0000000000000170 RSI: ffff92f0944d4c28 RDI: 00007ffc3b16c1a8
[   25.562275] RBP: ffff92f08159bce0 R08: fefefefefefefeff R09: 000000000000002c
[   25.569432] R10: 000000000000002c R11: ffff92f0944d5bb0 R12: 00007ffc3b16cff2
[   25.576588] R13: 00007ffc3b16c1a8 R14: 0000000000000001 R15: ffff92f0944d4ac0
[   25.583746] FS:  0000000000000000(0000) GS:ffff934e404c0000(0000)
knlGS:0000000000000000
[   25.591862] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   25.597624] CR2: ffffffffa5a8510a CR3: 000000010e33c003 CR4: 00000000003706e0
[   25.604780] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[   25.611936] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[   25.619092] Call Trace:
[   25.621545]  <TASK>
[   25.623648]  ? _copy_to_user+0x20/0x30
[   25.627409]  create_elf_tables+0x528/0x5a0
[   25.631520]  load_elf_binary+0x9e7/0xce0
[   25.635453]  bprm_execve+0x2bf/0x5c0
[   25.639040]  kernel_execve+0x2ad/0x2d0
[   25.642799]  run_init_process+0xa9/0xb0
[   25.646648]  ? rest_init+0xc0/0xc0
[   25.650059]  kernel_init+0x82/0x1a0
[   25.653558]  ret_from
_fork+0x1f/0x30
[   25.657145]  </TASK>