linux-kernel - Re: [PATCH 13/15] x86: add cmpxchg

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]

Message-ID: <4E555FBB.3020906@zytor.com>
Date:	Wed, 24 Aug 2011 13:31:55 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Christoph Lameter <cl@...ux.com>
CC:	Jeremy Fitzhardinge <jeremy@...p.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...e.hu>,
	the arch/x86 maintainers <x86@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Nick Piggin <npiggin@...nel.dk>,
	Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>
Subject: Re: [PATCH 13/15] x86: add cmpxchg_flag() variant

On 08/24/2011 12:27 PM, Christoph Lameter wrote:
> 
> Indeed for sete the size of the argument does not matter. Look at
> percpu_cmpxchg_double() and cmpxchg_double() in arch/x86/include for some
> of the functions I wrote. The sete is used to avoid the double word
> comparisons that would otherwise have been necessary.
> 
> But still the solution with the flags would save another instruction and
> the generated code would not be as ugly. For not only do you have an
> additional sete you will then also have to check the result again. This
> means at least two additional instruction.
> 

The sete is actually more expensive than the compare for the single-word
case.  The double-word case is a different matter.

	-hpa


--
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/