From: Linus Torvalds <torvalds@linux-foundation.org>
To: Scott Lurndal <scott.lurndal@3leafsystems.com>
Cc: David Howells <dhowells@redhat.com>,
mingo@elte.hu, tglx@linutronix.de, linux-arch@vger.kernel.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/3] X86: Optimise fls(), ffs() and fls64()
Date: Fri, 26 Mar 2010 10:42:46 -0700 (PDT) [thread overview]
Message-ID: <alpine.LFD.2.00.1003261038160.3721@i5.linux-foundation.org> (raw)
In-Reply-To: <20100326173730.GA27489@pendragon.3leafnetworks.com>
On Fri, 26 Mar 2010, Scott Lurndal wrote:
>
> I wonder if Intel's EM64 stuff makes this more deterministic, perhaps
> David's implementation would work for x86_64 only?
Limiting it to x86-64 would certainly remove all the worries about all the
historical x86 clones.
I'd still worry about it for future Intel chips, though. I absolutely
_detest_ relying on undocumented features - it pretty much always ends up
biting you eventually. And conditional writeback is actually pretty nasty
from a microarchitectural standpoint.
Linus
next prev parent reply other threads:[~2010-03-26 17:47 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <4BACCB4E.7010108@draigBrady.com>
2010-03-26 14:42 ` David Howells
2010-03-26 14:42 ` [PATCH 2/3] Adjust the comment on get_order() to describe the size==0 case David Howells
2010-03-26 14:42 ` [PATCH 3/3] Optimise get_order() David Howells
2010-03-26 17:23 ` [PATCH 1/3] X86: Optimise fls(), ffs() and fls64() Linus Torvalds
2010-03-26 17:37 ` Scott Lurndal
2010-03-26 17:42 ` Linus Torvalds [this message]
2010-04-06 13:57 ` Jamie Lokier
2010-04-06 14:40 ` Linus Torvalds
2010-03-26 17:42 ` David Howells
2010-03-26 17:45 ` Linus Torvalds
2010-03-26 17:58 ` Ralf Baechle
2010-03-26 18:03 ` Linus Torvalds
2010-03-26 18:16 ` Matthew Wilcox
2010-04-06 13:30 ` Matthew Wilcox
2010-04-14 11:49 ` David Howells
2010-04-14 14:30 ` Avi Kivity
2010-04-15 8:48 ` David Howells
2010-04-15 8:49 ` Avi Kivity
2010-04-15 11:41 ` Jamie Lokier
2010-03-26 17:52 ` Matthew Wilcox
2010-04-14 13:13 ` David Howells
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