On Fri, 22 Jan 2016, Waiman Long wrote:
The patch that I sent out is just a proof of concept to make sure that it can fix that particular case. I do plan to refactor it if I decide to go ahead with an official one. Unlike the OSQ, there can be no more than one waiter spinner as the wakeup function is directed to only the first task in the wait list and the spinning won't happen until the task is first woken up. In the worst case scenario, there are only 2 spinners spinning on the lock and the owner field, one from OSQ and one from the wait list. That shouldn't put too much cacheline contention traffic to the system.
Similarly, I guess we should also wakeup the next waiter in line after releasing the wait_lock via wake_q. This would allow the woken waiter a slightly better chance of finding the wait_lock free when continuing to take the mutex. Thanks, Davidlohr
