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Message-Id: <1208660817.12388.40.camel@localhost>
Date: Sat, 19 Apr 2008 20:06:57 -0700
From: Joe Perches <joe@...ches.com>
To: Matti Aarnio <matti.aarnio@...iler.org>
Cc: Harvey Harrison <harvey.harrison@...il.com>,
Alexander van Heukelum <heukelum@...lshack.com>,
Alexander van Heukelum <heukelum@...tmail.fm>,
LKML <linux-kernel@...r.kernel.org>
Subject: Re: Alternative implementation of the generic __ffs
On Sun, 2008-04-20 at 01:29 +0300, Matti Aarnio wrote:
> I am curious, why not take the code already in glibc ffs() for ARM ?
> That is, if the ffs() is all that important detail in kernel ?
Here's test results with the glibc ffs implementation.
(small const is still using slower add rather than or)
$ gcc -Os -fomit-frame-pointer ffs.c
$ ./a.out
Original: 3155 tics, 8331 tics
New: 4211 tics, 8793 tics
Smallest: 4019 tics, 7754 tics
Small const: 3552 tics, 6308 tics
glibc: 2816 tics, 6911 tics
Empty loop: 1516 tics, 2244 tics
$ gcc -O2 -fomit-frame-pointer ffs.c
$ ./a.out
Original: 3155 tics, 7828 tics
New: 4792 tics, 8825 tics
Smallest: 4401 tics, 7155 tics
Small const: 3539 tics, 5805 tics
glibc: 2720 tics, 7061 tics
Empty loop: 1516 tics, 2148 tics
$ gcc -O3 -fomit-frame-pointer ffs.c
$ ./a.out
Original: 3080 tics, 7706 tics
New: 4721 tics, 8663 tics
Smallest: 4334 tics, 7116 tics
Small const: 3466 tics, 5672 tics
glibc: 2649 tics, 6939 tics
Empty loop: 1444 tics, 2012 tics
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