16 mutext lock/unlocks per query?

[Rick Jones]

> the design expectation in bind9 was that mutex's were light weight
> (and indeed, with an mmap-based implementation that does TSI in user
> mode and avoids the syscall if the mutex was available, this is
> true) and so there are a hell of a lot ('scuse me, a HELL of a LOT)
> of fine grained mutex's rather than the "big lock" mentality we'd've
> followed if we'd thought these mutex's were going to be expensive.
Which platforms are considered as having lightweight mutexes?