From: Borislav Petkov <bp@alien8.de>
To: Rasmus Villemoes <mail@rasmusvillemoes.dk>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
x86-ml <x86@kernel.org>, Andy Lutomirski <luto@kernel.org>,
Josh Poimboeuf <jpoimboe@redhat.com>,
lkml <linux-kernel@vger.kernel.org>
Subject: Re: [RFC] Improve memset
Date: Fri, 13 Sep 2019 12:42:32 +0200 [thread overview]
Message-ID: <20190913104232.GA4190@zn.tnic> (raw)
In-Reply-To: <9dc9f1e6-5d19-167c-793d-2f4a5ebee097@rasmusvillemoes.dk>
On Fri, Sep 13, 2019 at 11:18:00AM +0200, Rasmus Villemoes wrote:
> Something like
>
> if (__builtin_constant_p(c) && __builtin_constant_p(n) && n <= 32)
> return __builtin_memset(dest, c, n);
>
> might be enough? Of course it would be sad if 32 was so high that this
> turned into a memset() call, but there's -mmemset-strategy= if one wants
> complete control. Though that's of course build-time, so can't consider
> differences between cpu models.
Yah, that seems to turn this:
memset(&tr, 0, sizeof(tr));
tr.b = b;
where sizeof(tr) < 32 into:
# ./arch/x86/include/asm/string_64.h:29: return __builtin_memset(dest, c, n);
movq $0, 16(%rsp) #, MEM[(void *)&tr + 8B]
movq $0, 24(%rsp) #, MEM[(void *)&tr + 8B]
# arch/x86/kernel/cpu/mce/amd.c:1070: tr.b = b;
movq %rbx, 8(%rsp) # b, tr.b
which is 2 u64 moves and the assignment of b at offset 8.
Question is, where we should put the size cap? I'm thinking 32 or 64
bytes...
Linus, got any suggestions?
Or should we talk to Intel hw folks about it...
--
Regards/Gruss,
Boris.
https://people.kernel.org/tglx/notes-about-netiquette
next prev parent reply other threads:[~2019-09-13 10:42 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-09-13 7:22 [RFC] Improve memset 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 [this message]
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
2019-09-14 9:29 Alexey Dobriyan
2019-09-14 11:39 ` Borislav Petkov
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20190913104232.GA4190@zn.tnic \
--to=bp@alien8.de \
--cc=jpoimboe@redhat.com \
--cc=linux-kernel@vger.kernel.org \
--cc=luto@kernel.org \
--cc=mail@rasmusvillemoes.dk \
--cc=torvalds@linux-foundation.org \
--cc=x86@kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).