[RFC PATCH-tip 2/6] locking/rwsem: Enable optional count-based spinning on reader

[Davidlohr Bueso]

On Tue, 14 Jun 2016, Waiman Long wrote:

>This patch provides a way for the kernel code to designate specific
>rwsems to be more aggressive in term of optimistic spinning that the
>writers will continue to spin for some additional count-based time to
>see if it can get the lock before sleeping. This aggressive spinning
>mode should only be used on rwsems where the readers are unlikely to
>go to sleep.

Yikes, exposing this sort of thing makes me _very_ uneasy, not to mention
the ad-hoc nature and its easiness to mess up. I'm not really for this, even
if it shows extraordinary performance boosts on benchmarks.

Thanks,
Davidlohr