perf: reduce overhead from getting cudaStream ptr

Author: matthewdouglas

bitsandbytes/functional.py

@@ -441,8 +441,9 @@ def is_on_gpu(tensors: Iterable[torch.Tensor]):
     return on_gpu
 
 
-def get_tensor_stream(tensor: Tensor) -> torch.cuda.Stream:
-    return torch.cuda.current_stream(tensor.device)
+def get_tensor_stream(tensor: Tensor) -> ct.c_void_p:
+    # We use the raw stream for performance reasons.
+    return ct.c_void_p(torch._C._cuda_getCurrentRawStream(tensor.device.index))
 
 
 def get_ptr(A: Optional[Tensor]) -> Optional[ct.c_void_p]: