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

Jeremy Fitzhardinge
2007-11-29T01:42:36Z

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