Messages in this thread | | | Subject | Re: [PATCH v2 1/7] locking/rwsem: check for active writer/spinner before wakeup | From | Davidlohr Bueso <> | Date | Fri, 08 Aug 2014 12:03:20 -0700 |
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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.
Thanks, Davidlohr
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