linux-kernel - Re: [PATCH 2/5] bitops: compile time optimization for hweight

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Date:	Sun, 14 Feb 2010 15:19:06 +0100
From:	Borislav Petkov <bp@...64.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Borislav Petkov <petkovbb@...glemail.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Wu Fengguang <fengguang.wu@...el.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Jamie Lokier <jamie@...reable.org>,
	Roland Dreier <rdreier@...co.com>,
	Al Viro <viro@...IV.linux.org.uk>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	Ingo Molnar <mingo@...e.hu>, Brian Gerst <brgerst@...il.com>
Subject: Re: [PATCH 2/5] bitops: compile time optimization for
 hweight_long(CONSTANT)

On Sun, Feb 14, 2010 at 01:23:35PM +0100, Peter Zijlstra wrote:
> On Sun, 2010-02-14 at 12:24 +0100, Borislav Petkov wrote:
> > 
> > So, if I understand you correctly, your suggestion might work, we
> > simply need to rename the lib/hweight.c versions to __sw_hweightN
> > and have <asm-generic/bitops/arch_hweight.h> have __arch_hweightN ->
> > __sw_hweightN wrappers in the default case, all arches which have an
> > optimized version will provide it in their respective bitops header...
> > 
> I'm not quite sure what the last 'it' refers to, does that refer to:
>  1) an __arch_hweightN() implementation, or
>  2) __arch_hweightN() -> __sw_hweightN() wrappers ?
> 
> If you meant 1, then yes.

Yes, I mean all architectures which have an optimized hweight will use
that optimized version in their __arch_hweightN while as a default
fallback for the remaining architectures we'll have __arch_hweightN() ->
__sw_hweightN() wrappers in <asm-generic/bitops/arch_hweight.h>.

-- 
Regards/Gruss,
Boris.

-
Advanced Micro Devices, Inc.
Operating Systems Research Center
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