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

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Date:	Mon, 28 Apr 2008 17:58:44 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Alexander van Heukelum <heukelum@...tmail.fm>
cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	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, Alexander van Heukelum wrote:
> > See patch below. It gives back the 1400 bytes on SPARC64 and other
> > platforms that have no instruction for find bit.
> 
> Hi,
> 
> I, personally, see this patch as a stopgap measure. The real problem
> is that the generic __ffs is inlined and ends up generating a lot
> of instructions.
> 
> Until the generic implementation of __ffs is fixed not to be an
> enormous inline function, this seems to be a reasonable thing
> to do, though it's a shame that the optimization is now default-
> off for architectures with a good implementation of __ffs.

Yup, it hasn't been there before and we explicitely enable it on
x86. If there are other archs which have a good one it's a nobrainer
to enable it.

Thanks,
	tglx

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