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

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Message-ID: <20080709193404.GC4804@elte.hu>
Date:	Wed, 9 Jul 2008 21:34:04 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Mike Travis <travis@....com>
Cc:	Jeremy Fitzhardinge <jeremy@...p.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Christoph Lameter <cl@...ux-foundation.org>,
	Jack Steiner <steiner@....com>, linux-kernel@...r.kernel.org
Subject: Re: [RFC 00/15] x86_64: Optimize percpu accesses

* Mike Travis <travis@....com> wrote:

> > This fragility makes me very nervous.  It seems hard enough to get 
> > this stuff working with current tools; making it work over the whole 
> > range of supported tools looks like its going to be hard.
> 
> (me too ;-)
> 
> Once I get a solid version working with (at least) gcc-4.2.4, then 
> regression testing with older tools will be easier, or at least a 
> table of results can be produced.

the problem is, we cannot just put it even into tip/master if there's no 
short-term hope of fixing a problem it triggers. gcc-4.2.3 is solid for 
me otherwise, for series of thousands of randomly built kernels.

can we just leave out the zero-based percpu stuff safely and could i 
test the rest of your series - or are there dependencies? I think 
zero-based percpu, while nice in theory, is probably just a very small 
positive effect so it's not a life or death issue. (or is there any 
deeper, semantic reason why we'd want it?)

	Ingo
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