Specifying Required Resources

Oftentimes, you may want to specify a task’s resource requirements (for example one task may require a GPU). Ray will automatically detect the available GPUs and CPUs on the machine (see Configuring Ray for more details).

Ray allows specifying a task’s resources requirements (e.g., CPU, GPU, and custom resources). The task will only run on a machine if there are enough resources available to execute the task.

# Specify required resources.
@ray.remote(num_cpus=4, num_gpus=2)
def my_function():
    return 1
// Specify required resources.
Ray.task(MyRayApp::myFunction).setResource("CPU", 1.0).setResource("GPU", 4.0).remote();
// Specify required resources.
ray::Task(MyFunction).SetResource("CPU", 1.0).SetResource("GPU", 4.0).Remote();


  • If you do not specify any resources, the default is 1 CPU resource and no other resources.

  • If specifying CPUs, Ray does not enforce isolation (i.e., your task is expected to honor its request).

  • If specifying GPUs, Ray does provide isolation in forms of visible devices (setting the environment variable CUDA_VISIBLE_DEVICES), but it is the task’s responsibility to actually use the GPUs (e.g., through a deep learning framework like TensorFlow or PyTorch).

The resource requirements of a task have implications for the Ray’s scheduling concurrency. In particular, the sum of the resource requirements of all of the concurrently executing tasks on a given node cannot exceed the node’s total resources.

Below are more examples of resource specifications:

# Ray also supports fractional resource requirements.
def h():
    return 1

# Ray support custom resources too.
@ray.remote(resources={'Custom': 1})
def f():
    return 1
// Ray aslo supports fractional and custom resources.
Ray.task(MyRayApp::myFunction).setResource("GPU", 0.5).setResource("Custom", 1.0).remote();
// Ray aslo supports fractional and custom resources.
ray::Task(MyFunction).SetResource("GPU", 0.5).SetResource("Custom", 1.0).Remote();


Besides compute resources, you can also specify an environment for a task to run in, which can include Python packages, local files, environment variables, and more—see Runtime Environments for details.