On Tue, Feb 03, 2015 at 11:43:36AM -0800, Tim Chen wrote: > That's true. We cannot have the lock grabbed by a new write > contender as any new writer contender of the lock will be > queued by the OSQ logic. Only the > thread doing the optimistic spin is attempting write lock. > In other word, switching of write owner of the rwsem to a new > owner cannot happen. Either write owner stay as the original one, or > we don't have a write owner. So using test of write owner > switching as an indicator of congestion is incorrect. > > If my reasoning above is sound, then the check > > + if (READ_ONCE(sem->owner)) > + return true; /* new owner, continue spinning */ > + > > is unnecessary and can be removed, as we cannot have a > new write owner of the rwsem, other than the thread > doing optimistic spinning.
I have read the rest of the thread; but the one thing that I didn't see is trylocks, trylocks can always come in an steal things regardless of the OSQ stuff. -- 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/
