On Fri, 05 Apr 2019, Waiman Long wrote:
With the commit 59aabfc7e959 ("locking/rwsem: Reduce spinlock contention in wakeup after up_read()/up_write()"), the rwsem_wake() forgoes doing a wakeup if the wait_lock cannot be directly acquired and an optimistic spinning locker is present. This can help performance by avoiding spinning on the wait_lock when it is contended.With the later commit 133e89ef5ef3 ("locking/rwsem: Enable lockless waiter wakeup(s)"), the performance advantage of the above optimization diminishes as the average wait_lock hold time become much shorter. By supporting rwsem lock handoff, we can no longer relies on the fact that the presence of an optimistic spinning locker will ensure that the lock will be acquired by a task soon. This can lead to missed wakeup and application hang. So the commit 59aabfc7e959 ("locking/rwsem: Reduce spinlock contention in wakeup after up_read()/up_write()") will have to be reverted. Signed-off-by: Waiman Long <[email protected]> --- kernel/locking/rwsem-xadd.c | 74 -------------------------------------
I very much like removing this code. It was rather crazy.
