linux-kernel - Re: [tip:x86/asm] x86: Prefer TZCNT over BFS

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] [day] [month] [year] [list]

Message-Id: <50583394020000780009BF8B@nat28.tlf.novell.com>
Date:	Tue, 18 Sep 2012 07:40:52 +0100
From:	"Jan Beulich" <JBeulich@...e.com>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	"Ingo Molnar" <mingo@...nel.org>, <tglx@...utronix.de>,
	"Linus Torvalds" <torvalds@...ux-foundation.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [tip:x86/asm] x86: Prefer TZCNT over BFS

>>> On 17.09.12 at 19:05, "H. Peter Anvin" <hpa@...or.com> wrote:
> Honestly, I don't see a reason to not do this unconditionally.  On
> anything but (pre-686-era) extremely old CPUs the cost of the extra
> prefix is zero.  On the really old CPUs the cost of the BSF instruction
> will dwarf the penalty cycle for the extra prefix, so the whole
> mechanism around doing it conditionally seems pointless.

I certainly don't mind re-submitting with the whole thing made
unconditional (implying that the prior version would be dropped
in any case).

Jan

--
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/