rwlock performance

[Iain Hibbert <plunky%rya-online.net@localhost>]

On Sat, 26 Dec 2009, Adam Hamsik wrote:

> RW locks have some performance problems, and they should not be used
> until it's needed. I think that same think can be accomplished by using
> reference counters and mutexes/cv variables.

Is that in general or is that just our implementation?  I mean, if the
same thing can be made out of mutex/refcount/condvar, and if rwlocks are
generally useful then can the rwlock code be reimplemented in a more
efficient manner?

iain