On Tue, 13 Jan 2009, Peter Zijlstra wrote:

Change mutex contention behaviour such that it will sometimes busy wait on
acquisition - moving its behaviour closer to that of spinlocks.

Okey, dokey. Looks reasonable, but I wonder if this part came from v8 and 
wasn't intentional:

+		if (atomic_xchg(&lock->count, -1) == 1) {
+			lock_acquired(&lock->dep_map, ip);
+			mutex_set_owner(lock);
+			preempt_enable();
+			return 0;
+		}

Now you're forcing the slow-path on unlock. Maybe it was intentional, 
maybe it wasn't. Did you perhaps mean

	if (atomic_cmpxchg(&lock->count, 1, 0) == 1) {

here? I thought we agreed it was safe, if only because it should be 
equivalent to just having done "mutex_trylock()" instead of a "real" lock 
sequence.

			Linus