On Mon, Feb 10, 2014 at 02:04:22PM -0800, Jason Low wrote: > On Mon, 2014-02-10 at 22:32 +0100, Peter Zijlstra wrote: > > Is adding that really much faster than the relatively straight path > > oqs_wait_next() would walk to bit the same exit? > > > > The only reason I pulled out the above cmpxchg() is because its the > > uncontended fast path, which seems like a special enough case. > > So it would avoid 2 extra checks (*lock == node) and (node->next) in the > oqs_wait_next() path, which aren't necessary when node->next != NULL. > > And I think node->next != NULL can be considered a special enough case > after the cmpxchg() fails because in the contended case, we're expecting > the node->next to be pointing at something. The only times node->next is > NULL after cmpxchg() fails are during a very small race window with the > osq_lock(), and when the next node is unqueuing due to need_resched, > which is also a very small window.
True all; now if only we had a useful benchmark so we could test if it makes a difference or not :-) -- 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/
