Messages in this thread | | | Subject | Re: [PATCH-tip v3 05/14] locking/rwsem: Remove rwsem_wake() wakeup optimization | From | Waiman Long <> | Date | Thu, 11 Apr 2019 11:55:02 -0400 |
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On 04/11/2019 03:25 AM, Peter Zijlstra wrote: > On Wed, Apr 10, 2019 at 02:42:22PM -0400, 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. > Does it make sense to make this patch #3 in this series? The less code > there is, the easier to review the other patches.
Yes, sure. I will move it up in the next version.
Cheers, Longman
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