On Tue, Jul 07, 2015 at 10:17:11AM +0100, Will Deacon wrote: > > > Thinking about it, can we kill _QW_WAITING altogether and set (cmpxchg > > > from 0) wmode to _QW_LOCKED in the write_lock slowpath, polling (acquire) > > > rmode until it hits zero? > > > > No, this is how we make the lock fair so that an incoming streams of > > later readers won't block a writer from getting the lock. > > But won't those readers effectively see that the lock is held for write > (because we set wmode to _QW_LOCKED before the existing reader had drained) > and therefore fall down the slow-path and get held up on the spinlock? Yes, that's the entire point. Once there's a writer pending, new readers should queue too. -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
