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

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Date:	Wed, 09 Jul 2008 14:03:45 -0700
From:	Mike Travis <travis@....com>
To:	Ingo Molnar <mingo@...e.hu>
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

Ingo Molnar wrote:
> * 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.

Great, I'll request we load gcc-4.2.3 on our devel server.

> 
> 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?)

I sort of assumed that zero-based would not make it into 2.6.26-rcX,
and no, reaching 4096 cpus does not require it.  The other patches
I've been submitting are more general and will fix possible panics
(like stack overflows, etc.)

Thanks,
Mike
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