Add comment for reference re PyTorch XLA 'race' issue

train.py

@@ -732,6 +732,11 @@ def evaluate(
             elif dev_env.type_cuda:
                 dev_env.synchronize()
 
+            # FIXME uncommenting this fixes race btw model `output`/`loss` and loss_m/accuracy_m meter input
+            # for PyTorch XLA GPU use.
+            # This issue does not exist for normal PyTorch w/ GPU (CUDA) or PyTorch XLA w/ TPU.
+            # loss.item()
+
             tracker.mark_iter_step_end()
             losses_m.update(loss, output.size(0))
             accuracy_m.update(output, target)