From: "H. Peter Anvin" <hpa@kernel.org>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: David Howells <dhowells@redhat.com>,
tglx@linutronix.de, mingo@redhat.com, x86@kernel.org,
linux-arch@vger.kernel.org
Subject: Re: [PATCH 1/3] X86_64: Optimise fls(), ffs() and fls64()
Date: Thu, 15 Dec 2011 10:12:21 -0800 [thread overview]
Message-ID: <4EEA3885.5050401@kernel.org> (raw)
In-Reply-To: <CA+55aFzanrQU2DQHxkE7cWBOwT7Xb=+LfmSNWoatDL-oiV6opA@mail.gmail.com>
On 12/14/2011 04:03 PM, Linus Torvalds wrote:
>
> I'm pretty sure that we had some chips that actually do write random
> stuff to the destination register when the input is zero.
>
> We relied on the "doesn't change the destination" at some point *long*
> ago, and it turned out not to work, but I can't remember what chip it
> was.
>
> I'm nervous about making this change even on x86-64 unless we add big
> comments about the old 32-bit change. Can somebody find the historic
> thing and a comment about which chip it was?
>
The ones I know of are some steppings of the 486.
-hpa
next prev parent reply other threads:[~2011-12-15 18:12 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-12-13 14:56 [PATCH 1/3] X86_64: Optimise fls(), ffs() and fls64() David Howells
2011-12-13 14:57 ` [PATCH 2/3] Adjust the comment on get_order() to describe the size==0 case David Howells
2011-12-19 18:45 ` H. Peter Anvin
2011-12-19 18:47 ` H. Peter Anvin
2011-12-20 15:09 ` Arnd Bergmann
2011-12-20 15:39 ` David Howells
2012-02-20 21:22 ` H. Peter Anvin
2011-12-20 16:09 ` hpanvin@gmail.com
2011-12-13 14:57 ` [PATCH 3/3] Optimise get_order() David Howells
2011-12-15 0:03 ` [PATCH 1/3] X86_64: Optimise fls(), ffs() and fls64() Linus Torvalds
2011-12-15 0:35 ` David Howells
2011-12-15 18:12 ` H. Peter Anvin [this message]
2011-12-15 21:29 ` H. Peter Anvin
2011-12-15 22:43 ` Arnd Bergmann
2011-12-15 23:58 ` H. Peter Anvin
2011-12-16 13:57 ` Arnd Bergmann
2011-12-16 15:27 ` H. Peter Anvin
2011-12-15 23:01 ` David Howells
2011-12-15 23:26 ` [tip:x86/asm] x86_64, asm: " tip-bot for David Howells
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