linux-kernel - Re: [GIT PULL] core/hweight changes for v2.6.35

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Date:	Fri, 13 Aug 2010 14:56:32 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Mike Frysinger <vapier.adi@...il.com>
CC:	Borislav Petkov <petkovbb@...glemail.com>,
	Chris Metcalf <cmetcalf@...era.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: [GIT PULL] core/hweight changes for v2.6.35

On 08/13/2010 02:42 PM, Mike Frysinger wrote:
> On Mon, May 17, 2010 at 17:21, Ingo Molnar wrote:
>>  arch/alpha/include/asm/bitops.h            |   18 +++++----
>>  arch/ia64/include/asm/bitops.h             |   11 +++--
>>  arch/sparc/include/asm/bitops_64.h         |   11 +++--
>>  arch/x86/include/asm/bitops.h              |    4 +-
>>  include/asm-generic/bitops/arch_hweight.h  |   25 ++++++++++++
>>  include/asm-generic/bitops/const_hweight.h |   42 ++++++++++++++++++++
>>  include/asm-generic/bitops/hweight.h       |    8 +---
> 
> did this miss Blackfin because the original patch was against the
> 2.6.34 tree ?  just wondering why it now build fails ...
> 
> doing a simple grep shows that the new "tile" arch may also be broken
> as it uses "hweight32" ...
> 
> considering __sw_hweightX only exist when the generic hweight is in
> play, wouldnt it make sense to have
> include/asm-generic/bitops/arch_hweight.h not always define things ?
> then most arches can simply pull in
> include/asm-generic/bitops/hweight.h without having to worry about the
> random inner details of hweight cruft.
> 

__sw_hweightX can exist even when generic hweight isn't in use per se,
because the arch implementation can wrapper the software implementation.
 This is the case on x86, for example -- most x86 CPUs don't have popcnt
yet, so on those the x86 implementation end up calling the
__sw_hweight*() implementations.

	-hpa
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