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

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Date:	Mon, 28 Apr 2008 09:54:37 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Thomas Gleixner <tglx@...utronix.de>
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, Thomas Gleixner wrote:

> 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.

That's not what I asked.

I asked whether there is a *reason* to optimize this and cause all these 
stupid problems.

Is there a real hot path anywhere that actually uses this and depends on 
it?

		Linus
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