AutoTVM on macOS with metal makes system crash

Hi! I’m trying to run the tutorial code of autotvm from To use metal backend, I changed the line 96 from target = "llvm" to target = "metal" and line 214 from ctx = tvm.cpu() to ctx = tvm.metal(). I can see the running log saying metal devices is initializing. (BTW it constantly spamming init messages, which may indicate something is going wrong) And after about 5 minutes, the system is frozen and unresponsive. Only a hard restart can recover. Is there any steps I have missed to use autoTVM with metal?