On Wed, 7 Jan 2009, Peter Zijlstra wrote: > > Do we really have to re-do all that code every loop? No, you're right, we can just look up the cpu once. Which makes Andrew's argument that "probe_kernel_address()" isn't in any hot path even more true. > Also, it would still need to do the funny: > > l_owner = ACCESS_ONCE(lock->owner) > if (l_owner && l_owner != thread) > break; Why? That would fall out of the if (lock->owner != thread) break; part. We don't actually care that it only happens once: this all has _known_ races, and the "cpu_relax()" is a barrier. And notice how the _caller_ handles the "owner == NULL" case by not even calling this, and looping over just the state in the lock itself. That was in the earlier emails. So this approach is actually pretty different from the case that depended on the whole spinlock thing. Linus -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
