[RFC] powerpc: use ticket spin lock for !CONFIG_PPC_SPLPAR

[Benjamin Herrenschmidt]

On Fri, 2015-03-13 at 14:09 +0800, Kevin Hao wrote:
> On Thu, Mar 12, 2015 at 04:24:10PM +0100, Torsten Duwe wrote:
> > But generally, which platforms would benefit most from this change?
> 
> In theory, the more cpus the platform has, the more serious the thundering
> herd problem is. So the latest platforms which has more cpus would benefit
> most.

In fact, pseries would be one to benefit ... it would be nice to find a
way to sort out the lock owner problem.

One idea I had was to keep the owners elsewhere, some kind of hash chain
of "taken locks" hashed on the lock address. There shouldn't be *that*
many locks held at a given point in time.

Trying to keep the owner in a separate & non-atomic part of the lock
proved being too hard due to how the lockref and generic code are
interwined, though maybe somebody smarter can find a trick :-)

Cheers,
Ben.