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

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Date:	Sun, 14 Feb 2010 11:12:23 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Borislav Petkov <bp@...64.org>
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	Borislav Petkov <petkovbb@...glemail.com>,
	Peter Zijlstra <peterz@...radead.org>,
	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 Thu, 2010-02-11 at 18:24 +0100, Borislav Petkov wrote:
> On Mon, Feb 08, 2010 at 10:59:45AM +0100, Borislav Petkov wrote:
> > Let me prep another version when I get back on Wed. (currently
> > travelling) with all the stuff we discussed to see how it would turn.
> 
> Ok, here's another version ontop of PeterZ's patch at
> http://lkml.org/lkml/2010/2/4/119. I need to handle 32- and 64-bit
> differently wrt to popcnt opcode so on 32-bit I do "popcnt %eax, %eax"
> while on 64-bit I do "popcnt %rdi, %rdi".

Right, so I don't like how you need to touch !x86 for this, and I think
that is easily avoidable by not making x86 include
asm-generic/bitops/arch_hweight.h.

If you then add __sw_hweightN() -> __arch_hweightN() wrappers in
arch_hweight.h, then you can leave const_hweight.h use __arch_hweightN()
and simply provide __arch_hweightN() from x86/include/asm/bitops.h


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