add support for CPU and for MPS. I had to change a few cosmetic things. I also discovered I think a bit of a bug, where I was casting wte to bfloat16 in the wrong place (the model init) instead of in init_weights

nanochat/common.py

@@ -89,11 +89,14 @@ def get_dist_info():
     else:
         return False, 0, 0, 1
 
-def compute_init(device_type="cuda"): # cuda|cpu
+def compute_init(device_type="cuda"): # cuda|cpu|mps
     """Basic initialization that we keep doing over and over, so make common."""
 
-    # CUDA is currently required
-    # assert torch.cuda.is_available(), "CUDA is needed for a distributed run atm"
+    assert device_type in ["cuda", "mps", "cpu"], "Invalid device type atm"
+    if device_type == "cuda":
+        assert torch.cuda.is_available(), "Your PyTorch installation is not configured for CUDA but device_type is 'cuda'"
+    if device_type == "mps":
+        assert torch.backends.mps.is_available(), "Your PyTorch installation is not configured for MPS but device_type is 'mps'"
 
     # Reproducibility
     torch.manual_seed(42)
@@ -101,11 +104,10 @@ def compute_init(device_type="cuda"): # cuda|cpu
         torch.cuda.manual_seed(42)
     # skipping full reproducibility for now, possibly investigate slowdown later
     # torch.use_deterministic_algorithms(True)
-    # torch.backends.cudnn.deterministic = True
-    # torch.backends.cudnn.benchmark = False
 
     # Precision
-    torch.set_float32_matmul_precision("high") # uses tf32 instead of fp32 for matmuls
+    if device_type == "cuda":
+        torch.set_float32_matmul_precision("high") # uses tf32 instead of fp32 for matmuls
 
     # Distributed setup: Distributed Data Parallel (DDP), optional, and requires CUDA
     ddp, ddp_rank, ddp_local_rank, ddp_world_size = get_dist_info()

nanochat/gpt.py

@@ -169,8 +169,6 @@ class GPT(nn.Module):
         cos, sin = self._precompute_rotary_embeddings(self.rotary_seq_len, head_dim)
         self.register_buffer("cos", cos, persistent=False) # persistent=False means it's not saved to the checkpoint
         self.register_buffer("sin", sin, persistent=False)
-        # Cast the embeddings from fp32 to bf16: optim can tolerate it and it saves memory: both in the model and the activations
-        self.transformer.wte.to(dtype=torch.bfloat16)
 
     def init_weights(self):
         self.apply(self._init_weights)
@@ -184,6 +182,9 @@ class GPT(nn.Module):
         head_dim = self.config.n_embd // self.config.n_head
         cos, sin = self._precompute_rotary_embeddings(self.rotary_seq_len, head_dim)
         self.cos, self.sin = cos, sin
+        # Cast the embeddings from fp32 to bf16: optim can tolerate it and it saves memory: both in the model and the activations
+        if self.transformer.wte.weight.device.type == "cuda":
+            self.transformer.wte.to(dtype=torch.bfloat16)
 
     def _init_weights(self, module):
         if isinstance(module, nn.Linear):

nanochat/loss_eval.py

@@ -33,7 +33,7 @@ def evaluate_bpb(model, batches, steps, token_bytes):
         loss2d = model(x, y, loss_reduction='none') # (B, T)
         loss2d = loss2d.view(-1) # flatten
         y = y.view(-1) # flatten
-        if (y < 0).any():
+        if (y.int() < 0).any(): # mps does not currently have kernel for < 0 for int64, only int32
             # slightly more complex code path if some target tokens are ignore_index (e.g. -1)
             # any target token < 0 is to be ignored: do NOT index token_bytes with negatives
             valid = y >= 0