Re: [PATCH] SLUB use cmpxchg_local

Christoph Lameter
2007-08-27T20:31:41Z

On Mon, 27 Aug 2007, Mathieu Desnoyers wrote:

> * Christoph Lameter (clameter@sgi.com) wrote:
> > On Mon, 27 Aug 2007, Peter Zijlstra wrote:
> >
> > > So, if the fast path can be done with a preempt off, it might be doable
> > > to suffer the slow path with a per cpu lock like that.
> >
> > Sadly the cmpxchg_local requires local per cpu data access. Isnt there
> > some way to make this less expensive on RT? Acessing cpu local memory is
> > really good for performance on NUMA since the data is optimally placed and
> > one can avoid/reduce locking if the process stays tied to the processor.
> >
>
> On the slow path, in slab_new, we already have to reenable interrupts
> because we can sleep. If we make sure that whenever we return to an irq
> disable code path we take the current per-cpu data structure again, can
> we make the preempt-disable/irq-disabled code paths O(1) ?

Not sure exactly what you are getting at?
This would mean running __alloc_pages tied to one processor even though
waiting is possible?