Re: mutexes, locks and so on...

[Eric Haszlakiewicz <erh%nimenees.com@localhost>]

On Tue, Nov 16, 2010 at 09:44:18AM -0800, Matt Thomas wrote:
> On Nov 16, 2010, at 9:10 AM, Alan Barrett wrote:
> > Please could somebody on the "eat your CAS whether you like it or not"
> > side of the fence explain why the following idea would not work:
> > 
> > On Sat, 13 Nov 2010, der Mouse wrote:
> >> Arches without a sufficiently general CAS[%] do not define
> >> ATOMIC_OPS_USE_CAS and provides their own implementations of mutexes,
> >> spinlocks, whatever.
> 
> Because that flexibility already exists.  A port can provide a full
> mutex or rwlock implementation or use the default based on CAS primitives.
> 
> I think the question is about more about the naked use of atomic_cas_xxx
> which are scattered around in the kernel.  

Wouldn't those calls just use the slow implementation of CAS?  I haven't
heard anyone saying that the vax port shouldn't (continue to) implement ai
CAS operation, just that it shouldn't be used for mutexes.  And if those 
naked uses of atomic_cas_xxx cause unreasonable slowness for that port, 
well that's a separate problem.

eric