linux-kernel - Re: [RFC 00/15] x86_64: Optimize percpu accesses

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Message-ID: <48767F4F.1010209@zytor.com>
Date:	Thu, 10 Jul 2008 17:29:51 -0400
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Christoph Lameter <cl@...ux-foundation.org>
CC:	Jeremy Fitzhardinge <jeremy@...p.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Ingo Molnar <mingo@...e.hu>, Mike Travis <travis@....com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jack Steiner <steiner@....com>, linux-kernel@...r.kernel.org,
	Arjan van de Ven <arjan@...radead.org>
Subject: Re: [RFC 00/15] x86_64: Optimize percpu accesses

Christoph Lameter wrote:
> Jeremy Fitzhardinge wrote:
> 
>> Percpu on i386 hasn't been a point of discussion.  It works fine, and
>> has been working fine for a long time.  The same mechanism would work
>> fine on x86-64.  Its only "issue" is that it doesn't support the broken
>> gcc abi for stack-protector.
> 
> Well that is one thing and then the scaling issues, and the support of the new cpu allocator, new arch independent cpu operations etc.
> 
>> The problem is all zero-based percpu on x86-64.
> 
> The zero based stuff will enable a lot of things. Please have a look at the cpu_alloc patchsets.
> 

No argument this work is worthwhile.  The main issues on the table is 
the particular choice of offsets, and the handling of the virtual space 
-- I believe 2 MB mappings are too large, except perhaps as an option.

	-hpa

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