[PATCH] idr: Use this_cpu_ptr() for percpu_ida

From: Kent Overstreet
Date: Wed Aug 07 2013 - 15:57:40 EST

On Wed, Aug 07, 2013 at 07:40:15PM +0000, Christoph Lameter wrote:
> On Wed, 7 Aug 2013, Kent Overstreet wrote:
> > I was breaking it apart because I was using this_cpu elsewhere too - for
> > the bitmap of which cpus have non empty freelists.
> this_cpu can be retrieved with smp_processor_id().
> > Or is this_cpu_ptr() doing something smarter than per_cpu_ptr(ptr,
> > smp_processer_id())? There's so many variants I'm not 100% sure they're
> > the same.
> Yes it is. It uses a sepecial register that contains the offset of this
> cpus per cpu area instead of going through the table of all processor
> offsets. Its less code.

Alright, well here's a fixup patch - untested for the moment though.

One thing that was bugging me - I was never able to figure out for sure
if smp_processor_id() returns a number in the range [0, nr_cpu_ids), at
least I couldn't find where it was documented - could you tell me if
that's true?