On Thu, 2014-07-03 at 16:35 -0400, Waiman Long wrote: > I do see a point in reducing the size of the rwsem structure. However, I > don't quite understand the point of converting pointers in the > optimistic_spin_queue structure to atomic_t. The structure is cacheline > aligned and there is no saving in size. Converting them to atomic_t does > have a bit of additional overhead of converting the encoded cpu number > back to the actual pointer. > > So my suggestion is to just change what is stored in the mutex and rwsem > structure to atomic_t, but keep the pointers in the > optimistic_spin_queue structure.
Peter, would you prefer going with the above? If we were to keep the pointers to the next and prev nodes in the struct optimistic_spin_queue instead of converting them to atomic_t to store their cpu #, we'd still need to keep track of the cpu #. In the unqueue phase of osq_lock, we might have to reload prev = node->prev which we then may cmpxchg() it with the lock tail. The method we can think of so far would be to add a regular int variable to optimistic_spin_queue and initialize it to the CPU #, during the time we also initialize node->locked and node->next at the beginning of osq_lock. The cost wouldn't be much of an issue since optimistic_spin_queue is cache aligned. -- 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/
