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

[Waiman Long]

On 06/14/2016 02:27 PM, Davidlohr Bueso wrote:
> 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

I understand your concern. I will see if there is a way to autotune 
instead of using explicit enablement.

Cheers,
Longman