[Core] Do not convert gpu id to int (#9744)

Co-authored-by: Richard Liaw <rliaw@berkeley.edu>

doc/source/actors.rst

@@ -72,8 +72,8 @@ Resources with Actors
 You can specify that an actor requires CPUs or GPUs in the decorator. While Ray has built-in support for CPUs and GPUs, Ray can also handle custom resources.
 
 When using GPUs, Ray will automatically set the environment variable ``CUDA_VISIBLE_DEVICES`` for the actor after instantiated. The actor will have access to a list of the IDs of the GPUs
-that it is allowed to use via ``ray.get_gpu_ids()``. This is a list of integers,
-like ``[]``, or ``[1]``, or ``[2, 5, 6]``.
+that it is allowed to use via ``ray.get_gpu_ids(as_str=True)``. This is a list of strings,
+like ``[]``, or ``['1']``, or ``['2', '5', '6']``. Under some circumstances, the IDs of GPUs could be given as UUID strings instead of indices (see the `CUDA programming guide <https://docs.nvidia.com/cuda/cuda-c-programming-guide/index.html#env-vars>`__).
 
 .. code-block:: python
 

doc/source/using-ray-with-gpus.rst

@@ -33,8 +33,8 @@ remote decorator.
       print("ray.get_gpu_ids(): {}".format(ray.get_gpu_ids()))
       print("CUDA_VISIBLE_DEVICES: {}".format(os.environ["CUDA_VISIBLE_DEVICES"]))
 
-Inside of the remote function, a call to ``ray.get_gpu_ids()`` will return a
-list of integers indicating which GPUs the remote function is allowed to use.
+Inside of the remote function, a call to ``ray.get_gpu_ids(as_str=True)`` will return a
+list of strings indicating which GPUs the remote function is allowed to use.
 Typically, it is not necessary to call ``ray.get_gpu_ids()`` because Ray will
 automatically set the ``CUDA_VISIBLE_DEVICES`` environment variable.