linux-kernel - Re: [PATCH] bitops: simplify generic bit finding functions

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Message-ID: <alpine.LFD.1.10.0804281845250.3261@apollo.tec.linutronix.de>
Date:	Mon, 28 Apr 2008 18:47:50 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
cc:	Harvey Harrison <harvey.harrison@...il.com>,
	Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	David Miller <davem@...emloft.net>
Subject: Re: [PATCH] bitops: simplify generic bit finding functions

On Mon, 28 Apr 2008, Linus Torvalds wrote:
> >
> > How about making the optimization controlled by a config switch so
> > arch maintainers can decide whether they want to enable the constant
> > optimization or unconditionally call the lib function ?
> 
> No.
> 
> This is just making that damn header line look worse and worse.
> 
> Is there a _reason_ to optimize this stupid function this way?

On architectures which have a find bit instruction we can replace the
call to the library function by a single instruction when the size of
the bitmap is less/equal bits per long and when the bitnr is a
constant.

Thanks,
	tglx


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