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From: Alexey Dobriyan <adobriyan@gmail.com>
To: bp@alien8.de
Cc: linux-kernel@vger.kernel.org, mingo@kernel.org, x86@kernel.org,
	linux@rasmusvillemoes.dk, torvalds@linux-foundation.org
Subject: Re: [RFC] Improve memset
Date: Sat, 14 Sep 2019 12:29:15 +0300	[thread overview]
Message-ID: <20190914092915.GA17409@avx2> (raw)

> Instead of calling memset:
> 
> ffffffff8100cd8d:       e8 0e 15 7a 00          callq  ffffffff817ae2a0 <__memset>
> 
> and having a JMP inside it depending on the feature supported, let's simply
> have the REP; STOSB directly in the code:
> 
> ...
> ffffffff81000442:       4c 89 d7                mov    %r10,%rdi
> ffffffff81000445:       b9 00 10 00 00          mov    $0x1000,%ecx
> 
> <---- new memset
> ffffffff8100044a:       f3 aa                   rep stos %al,%es:(%rdi)
> ffffffff8100044c:       90                      nop
> ffffffff8100044d:       90                      nop
> ffffffff8100044e:       90                      nop

You can fit entire "xor eax, eax; rep stosb" inside call instruction.

> /* clobbers used by memset_orig() and memset_rep_good() */
>                 : "rsi", "rdx", "r8", "r9", "memory");

eh... I'd just drop it. These registers screw up everything.

Time to rebase memset0().

             reply	other threads:[~2019-09-14  9:29 UTC|newest]

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-09-14  9:29 Alexey Dobriyan [this message]
2019-09-14 11:39 ` [RFC] Improve memset Borislav Petkov
  -- strict thread matches above, loose matches on Subject: below --
2019-09-13  7:22 Borislav Petkov
2019-09-13  7:35 ` Ingo Molnar
2019-09-13  7:50   ` Borislav Petkov
2019-09-13  8:51 ` Rasmus Villemoes
2019-09-13  9:00 ` Linus Torvalds
2019-09-13  9:18   ` Rasmus Villemoes
2019-09-13 10:42     ` Borislav Petkov
2019-09-13 16:36       ` Borislav Petkov
2019-09-16  9:18         ` Rasmus Villemoes
2019-09-16 17:25           ` Linus Torvalds
2019-09-16 17:40             ` Andy Lutomirski
2019-09-16 21:29               ` Linus Torvalds
2019-09-16 23:13                 ` Andy Lutomirski
2019-09-16 23:26                   ` Linus Torvalds
2019-09-17  8:15             ` Borislav Petkov
2019-09-17 10:55             ` David Laight
2019-09-17 20:10 ` Josh Poimboeuf
2019-09-17 20:45   ` Linus Torvalds
2019-09-19 12:55     ` Borislav Petkov
2019-09-19 12:49   ` Borislav Petkov

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