linux-kernel - Re: Big git diff speedup by avoiding x86 "fast string" memcmp

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Wed, 15 Dec 2010 16:54:50 +1100
From:	Nick Piggin <npiggin@...nel.dk>
To:	Américo Wang <xiyou.wangcong@...il.com>
Cc:	Nick Piggin <npiggin@...il.com>,
	"J. R. Okajima" <hooanon05@...oo.co.jp>,
	Nick Piggin <npiggin@...nel.dk>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-arch@...r.kernel.org, x86@...nel.org,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: Big git diff speedup by avoiding x86 "fast string" memcmp

On Wed, Dec 15, 2010 at 12:38:40PM +0800, Américo Wang wrote:
> On Mon, Dec 13, 2010 at 07:25:05PM +1100, Nick Piggin wrote:
> >On Mon, Dec 13, 2010 at 6:29 PM, J. R. Okajima <hooanon05@...oo.co.jp> wrote:
> >> But is the "rep cmp has quite a long latency" issue generic for all x86
> >> architecture, or Westmere system specific?
> >
> >I don't believe it is Westmere specific. Intel and AMD have
> >been improving these instructions in the past few years, so
> >Westmere is probably as good or better than any.
> >
> >That said, rep cmp may not be as heavily optimized as the
> >set and copy string instructions.
> >
> >In short, I think the change should be suitable for all x86 CPUs,
> >but I would like to hear more opinions or see numbers for other
> >cores.
> >
> 
> How about other arch? If this is only for x86, shouldn't it be
> protected by CONFIG_X86?

That's what I would like to know, but I suspect that for very short
strings we are dealing with, the custom loop will be fine for
everybody.

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/