On Sun, 2014-08-10 at 17:41 -0400, Waiman Long wrote: > 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.
But afaict you cannot have LOCKDEP without enabling DEBUG_MUTEX (but not necessarily vice-versa). Both are quite intertwined within other debugging dependencies/options. Thanks, Davidlohr -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
