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.

Python

# Specify required resources.
@ray.remote(num_cpus=4, num_gpus=2)
def my_function():
    return 1

Java

// Specify required resources.
Ray.task(MyRayApp::myFunction).setResource("CPU", 1.0).setResource("GPU", 4.0).remote();

C++

// Specify required resources.
ray::Task(MyFunction).SetResource("CPU", 1.0).SetResource("GPU", 4.0).Remote();

Note

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:

Python

# Ray also supports fractional resource requirements.
@ray.remote(num_gpus=0.5)
def h():
    return 1

# Ray support custom resources too.
@ray.remote(resources={'Custom': 1})
def f():
    return 1

Java

// Ray aslo supports fractional and custom resources.
Ray.task(MyRayApp::myFunction).setResource("GPU", 0.5).setResource("Custom", 1.0).remote();

C++

// Ray aslo supports fractional and custom resources.
ray::Task(MyFunction).SetResource("GPU", 0.5).SetResource("Custom", 1.0).Remote();

Tip

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.

Ray 2.0.0

Specifying Required Resources¶