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

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Message-Id: <1209394723.22937.1250267923@webmail.messagingengine.com>
Date:	Mon, 28 Apr 2008 16:58:43 +0200
From:	"Alexander van Heukelum" <heukelum@...tmail.fm>
To:	"Linus Torvalds" <torvalds@...ux-foundation.org>,
	"Harvey Harrison" <harvey.harrison@...il.com>,
	"David S. Miller" <davem@...emloft.net>
Cc:	"Ingo Molnar" <mingo@...e.hu>,
	"Andrew Morton" <akpm@...ux-foundation.org>,
	"LKML" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] bitops: simplify generic bit finding functions

On Sun, 27 Apr 2008 13:26:34 -0700 (PDT), "Linus Torvalds"
<torvalds@...ux-foundation.org> said:
> On Sun, 27 Apr 2008, Harvey Harrison wrote:
> >
> > No need for a sentinal if we explicitly catch the no bits/all bits set
> > cases, make it clear they are special cases returning size/BITS_PER_LONG.
> 
> These things need to be re-done anyway. David already complained that the 
> thing inlines to something much much too big.
> 
> Let's just make it not be an inline at all.

Hello,

I think that's the wrong way to go about it. The problem that David
Miller pointed out was that the small-bitmap optimization caused an
inliningdisaster. Apparently, the generic version of __ffs is very
big on sparc64. In my opinion the implementation of __ffs should be
made out of line. If you move the wrapper of find_first_bit etc
out of line, all possibilities of optimization will be destroyed.
Better to remove them completely, then.

Greetings,
    Alexander

> 		Linus
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-- 
  Alexander van Heukelum
  heukelum@...tmail.fm

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