Messages in this thread | | | Date | Sun, 10 Aug 2014 17:41:38 -0400 | From | Waiman Long <> | Subject | Re: [PATCH v2 1/7] locking/rwsem: check for active writer/spinner before wakeup |
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On 08/08/2014 03:03 PM, Davidlohr Bueso wrote: > On Fri, 2014-08-08 at 14:30 -0400, Waiman Long wrote: >> I have 2 issues about this. First of all, the timing windows between >> atomic_set() and mutex_has_owner() check is really small, I doubt it >> will be that effective. > That is true, which is why I didn't bother showing any performance data > in the changelog. However, more important than any performance, avoiding > bogus wakeups is the _right_ thing to do when allowing lock stealing. > >> Secondly, I think you may need to call >> mutex_release() and debug_mutex_unlock() to make the debugging code >> work, but they seems to be called only under the wait_lock. So I think >> there is more work that need to be done before this patch is ready. > When !DEBUG both mutex_release() and debug_mutex_unlock() should be > no-ops. So this allows us to do the mutex_has_owner() check *without* > holding the wait_lock. > > When DEBUG is set, we don't even bother calling mutex_has_owner(), so > nothing changes. > > I don't understand your concern.
It is true I forgot the fact that MUTEX_SPIN_ON_OWNER is disabled when DEBUG_MUTEX is on. However, mutex_release is controlled by the LOCKDEP config variable which is independent of DEBUG_MUTEX. So it is still a concern.
-Longman
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