linux-kernel - Re: why does the macro "ZERO

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Message-ID: <466E0258.2070407@yahoo.com.au>
Date:	Tue, 12 Jun 2007 12:18:00 +1000
From:	Nick Piggin <nickpiggin@...oo.com.au>
To:	"H. Peter Anvin" <hpa@...or.com>
CC:	William Lee Irwin III <wli@...omorphy.com>,
	"Robert P. J. Day" <rpjday@...dspring.com>,
	Satyam Sharma <satyam.sharma@...il.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Ralf Baechle <ralf@...ux-mips.org>
Subject: Re: why does the macro "ZERO_PAGE" take an argument?

H. Peter Anvin wrote:
> William Lee Irwin III wrote:
> 
>>Robert P. J. Day wrote:
>>
>>>>although it's not clear where in the source tree are the invocations
>>>>that would actually make a difference to a MIPS system, which is why
>>>>i've CC'ed ralf on this.  i'm sure he can clear this up. :-)
>>
>>On Thu, Jun 07, 2007 at 10:32:29AM -0700, H. Peter Anvin wrote:
>>
>>>x86 could also benefit from coloured zeropages.  In fact, I thought it
>>>already had them (K8 wants as many as 8.)
>>
>>How would one demonstrate the beneficial effect of such?
> 
> 
> Dean Gaudet at Transmeta did some benchmarking using SPEC.  If I recall
> his numbers correctly (this is from memory, mind you) on Transmeta
> Efficeon, which has 2-way virtual cache tagging with hardware recovery,
> zeropage coloring was a 1.5% performance improvement.

I'm surprised that the benchmark made such use of zero pages so as to
be worthwhile. I'm sitting on a patch which removes the zero page from
the page fault fastpath completely which I'd like to try out in -mm...

-- 
SUSE Labs, Novell Inc.
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