On Tue, Nov 07, 2017 at 04:18:06PM -0500, Waiman Long wrote: > Currently, all the lock waiters entering the slowpath will do one > lock stealing attempt to acquire the lock. That helps performance, > especially in VMs with over-committed vCPUs. However, the current > pvqspinlocks still don't perform as good as unfair locks in many cases. > On the other hands, unfair locks do have the problem of lock starvation > that pvqspinlocks don't have. > > This patch combines the best attributes of an unfair lock and a > pvqspinlock into a hybrid lock with 2 modes - queued mode & unfair > mode. A lock waiter goes into the unfair mode when there are waiters > in the wait queue but the pending bit isn't set. Otherwise, it will > go into the queued mode waiting in the queue for its turn. >
> > Signed-off-by: Waiman Long <[email protected]> Reviewed-by: Eduardo Valentin <[email protected]> -- All the best, Eduardo Valentin
