You can try disabling ACPI rather than APIC, too -- or disable both of them.
However, this isn't a deadlock. In a deadlock, there's 0% CPU utilization -- both threads (or all threads, or all processes, or whatever's involved in the deadlock) are waiting for each other to do something, using no CPU. This happens if thread 1 calls wait on lock 1, and thread 2 calls wait on lock 2, then they each try to wait on the other lock. They'll sleep forever, because neither one can wake up to release its lock.
What you're seeing, if it's any kind of locking issue, is a livelock, where the processes involved are spinning in some sort of busy-wait loop. However, AFAIK, X is not multithreaded -- and there's only one process running. So it can't deadlock or livelock with other threads. I therefore doubt that it's any kind of locking -- though I don't have source either, so it could be some resource contention on the card that we can't see.