Re: [RFC PATCH-tip v2 2/6] locking/rwsem: Stop active read lock ASAP

Waiman Long
2016-06-16T21:25:35Z

On 06/15/2016 10:14 PM, Davidlohr Bueso wrote:
> On Wed, 15 Jun 2016, Waiman Long wrote:
>
>> I think there will be a little bit of performance impact for a
>> workload that produce just the right amount of rwsem contentions.
>
> I'm not saying the change doesn't make sense, but this is the sort of
> thing that will show nice numbers in one workload and go bite you in
> another.
>
> Thanks,
> Davidlohr

I would certainly agree if the additional atomic op is in the fastpath.
Since it is in the slowpath, one additional atomic op will just be a
small part of the whole rwsem_down_read_failed() function. I doubt if
the performance degradation, if any, can be even noticeable.

Cheers,
Longman