From: "Brian F. G. Bidulock" <bidulock@openss7.org>
To: Andi Kleen <ak@suse.de>
Cc: Andrew Morton <akpm@osdl.org>,
adilger@clusterfs.com, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] use unlikely() for current_kernel_time() loop
Date: Thu, 8 Jun 2006 01:43:26 -0600 [thread overview]
Message-ID: <20060608014326.B12202@openss7.org> (raw)
In-Reply-To: <200606080907.26350.ak@suse.de>; from ak@suse.de on Thu, Jun 08, 2006 at 09:07:26AM +0200
Andi,
On Thu, 08 Jun 2006, Andi Kleen wrote:
>
> AFAIK gcc mostly uses the probability information for block reordering
> to make the fast path fall through without jumps.
After a quick try on RH EL4 gcc 3.4.4-2 it appears that
-fno-reorder-blocks indeed defeats __builtin_expect() as you
say. (Which is rather bizarre as __builtin_expect() no longer
does what one expects.) I think that I'm going to strip it out
for my externally compiled modules. Otherwise, the source code
rearrangements necessary to get the same effect will make the
source code unreadable and generate larger code, which I think
is worse than those effects on the assembler code.
Thanks again.
--brian
next prev parent reply other threads:[~2006-06-08 7:43 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-06-07 17:36 [PATCH] use unlikely() for current_kernel_time() loop Andreas Dilger
2006-06-08 2:28 ` Andi Kleen
2006-06-08 5:01 ` Andrew Morton
2006-06-08 5:39 ` Andi Kleen
2006-06-08 6:41 ` Brian F. G. Bidulock
2006-06-08 6:51 ` Andi Kleen
2006-06-08 7:00 ` Brian F. G. Bidulock
2006-06-08 7:07 ` Andi Kleen
2006-06-08 7:43 ` Brian F. G. Bidulock [this message]
2006-06-08 8:59 ` Brian F. G. Bidulock
2006-06-08 9:14 ` Andi Kleen
2006-06-08 9:36 ` Brian F. G. Bidulock
2006-06-08 10:20 ` Andi Kleen
2006-06-08 10:50 ` Brian F. G. Bidulock
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