Re: [patch 05/14] percpu: Use a Kconfig variable to configure archspecific percpu setup

[Jeremy Fitzhardinge]

Christoph Lameter wrote:
> On Wed, 28 Nov 2007, Jeremy Fitzhardinge wrote:
>
>   
>> I don't see the problem.  The way i386 does it inherently supports
>> per-cpu data very early on (it uses the prototype percpu section until
>> the real percpu values are set up).
>>     
>
> Ok so we could do that for x86_64 as well? There is more complicated 
> bootstrap since i386 does not support NUMA aware placement of per cpu 
> areas.
>   

Don't think it matters either way.  Before percpu is allocated, NUMA
issues don't matter.  Once they are - by whatever mechanism - you can
set the segment bases up appropriately.  The fact that you chose to put
percpu data at address X doesn't affect the percpu mechanism one way or
the other.

> percpu references are quite frequent already (vm statistics) and will be 
> more frequent after we have converted the per cpu arrays to per cpu 
> allocations.
>   

Well, I think the point is moot, because x86 will always use 32-bit
offsets.  Each reference will only be 1 byte bigger than a normal
variable reference.

    J
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