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().
next 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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