Re: [Xen-devel] [PATCH v9 05/19] qspinlock: Optimize for smaller NR_CPUS

[Waiman Long <waiman.long@xxxxxx>]

On 04/17/2014 11:51 AM, Peter Zijlstra wrote:
> On Thu, Apr 17, 2014 at 11:03:57AM -0400, Waiman Long wrote:
> > @@ -48,6 +53,9 @@
> >    * We can further change the first spinner to spin on a bit in the lock word
> >    * instead of its node; whereby avoiding the need to carry a node from lock to
> >    * unlock, and preserving API.
> > + *
> > + * N.B. The current implementation only supports architectures that allow
> > + *      atomic operations on smaller 8-bit and 16-bit data types.
> >    */
> Only for the _Q_PENDING_BITS == 8 case, the other case should still be
> fine.
Yes, but _Q_PENDING_BITS is controlled by NR_CPUS which, for almost all 
the distributions, is less than 16K which means _Q_PENDING_BITS will 
always be set to 8, especially for non-x86 architectures.
-Longman

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