This document describes Ray Tune, a hyperparameter tuning framework for long-running tasks such as RL and deep learning training. It has the following features:
- Early stopping algorithms such as `Median Stopping Rule <https://research.google.com/pubs/pub46180.html>`__ and `HyperBand <https://arxiv.org/abs/1603.06560>`__.
- Integration with visualization tools such as `TensorBoard <https://www.tensorflow.org/get_started/summaries_and_tensorboard>`__, `rllab's VisKit <https://media.readthedocs.org/pdf/rllab/latest/rllab.pdf>`__, and a `parallel coordinates visualization <https://en.wikipedia.org/wiki/Parallel_coordinates>`__.
- Flexible trial variant generation, including grid search, random search, and conditional parameter distributions.
- Resource-aware scheduling, including support for concurrent runs of algorithms that may themselves be parallel and distributed.
This script runs a small grid search over the ``my_func`` function using Ray Tune, reporting status on the command line until the stopping condition of ``mean_accuracy >= 100`` is reached (for metrics like _loss_ that decrease over time, specify `neg_mean_loss <https://github.com/ray-project/ray/blob/master/python/ray/tune/result.py#L40>`__ as a condition instead):
In order to report incremental progress, ``my_func`` periodically calls the ``reporter`` function passed in by Ray Tune to return the current timestep and other metrics as defined in `ray.tune.result.TrainingResult <https://github.com/ray-project/ray/blob/master/python/ray/tune/result.py>`__.
Ray Tune logs trial results to a unique directory per experiment, e.g. ``~/ray_results/my_experiment`` in the above example. The log records are compatible with a number of visualization tools:
Finally, to view the results with a `parallel coordinates visualization <https://en.wikipedia.org/wiki/Parallel_coordinates>`__, open `ParallelCoordinatesVisualization.ipynb <https://github.com/ray-project/ray/blob/master/python/ray/tune/ParallelCoordinatesVisualization.ipynb>`__ as follows and run its cells:
In the above example, we specified a grid search over two parameters using the ``grid_search`` helper function. Ray Tune also supports sampling parameters from user-specified lambda functions, which can be used in combination with grid search.
The following shows grid search over two nested parameters combined with random sampling from two lambda functions. Note that the value of ``beta`` depends on the value of ``alpha``, which is represented by referencing ``spec.config.alpha`` in the lambda function. This lets you specify conditional parameter distributions.
By default, each random variable and grid search point is sampled once. To take multiple random samples or repeat grid search runs, add ``repeat: N`` to the experiment config. E.g. in the above, ``"repeat": 10`` repeats the 3x3 grid search 10 times, for a total of 90 trials, each with randomly sampled values of ``alpha`` and ``beta``.
For more information on variant generation, see `variant_generator.py <https://github.com/ray-project/ray/blob/master/python/ray/tune/variant_generator.py>`__.
To reduce costs, long-running trials can often be early stopped if their initial performance is not promising. Ray Tune allows early stopping algorithms to be plugged in on top of existing grid or random searches. This can be enabled by setting the ``scheduler`` parameter of ``run_experiments``, e.g.
An example of this can be found in `hyperband_example.py <https://github.com/ray-project/ray/blob/master/python/ray/tune/examples/hyperband_example.py>`__. The progress of one such HyperBand run is shown below.
Note that some trial schedulers such as HyperBand require your Trainable to support checkpointing, which is described in the next section. Checkpointing enables the scheduler to multiplex many concurrent trials onto a limited size cluster.
Currently we support the following early stopping algorithms, or you can write your own that implements the `TrialScheduler <https://github.com/ray-project/ray/blob/master/python/ray/tune/trial_scheduler.py>`__ interface.
To enable checkpoint / resume, you must subclass ``Trainable`` and implement its ``_train``, ``_save``, and ``_restore`` abstract methods `(example) <https://github.com/ray-project/ray/blob/master/python/ray/tune/examples/hyperband_example.py>`__: Implementing this interface is required to support resource multiplexing in schedulers such as HyperBand.
Ray Tune runs each trial as a Ray actor, allocating the specified GPU and CPU ``resources`` to each actor (defaulting to 1 CPU per trial). A trial will not be scheduled unless at least that amount of resources is available in the cluster, preventing the cluster from being overloaded.
If your trainable function / class creates further Ray actors or tasks that also consume CPU / GPU resources, you will also want to set ``driver_cpu_limit`` or ``driver_gpu_limit`` to tell Ray not to assign the entire resource reservation to your top-level trainable function, as described in `trial.py <https://github.com/ray-project/ray/blob/master/python/ray/tune/trial.py>`__. For example, if a trainable class requires 1 GPU itself, but will launch 4 actors each using another GPU, then it should set ``"gpu": 5, "driver_gpu_limit": 1``.
You can modify an ongoing experiment by adding or deleting trials using the Tune Client API. To do this, verify that you have the ``requests`` library installed:
..code-block:: bash
$ pip install requests
To use the Client API, you can start your experiment with ``with_server=True``:
Then, on the client side, you can use the following class. The server address defaults to ``localhost:4321``. If on a cluster, you may want to forward this port so that you can use the Client on your local machine.
..autoclass:: ray.tune.web_server.TuneClient
:members:
For an example notebook for using the Client API, see the `Client API Example <https://github.com/ray-project/ray/tree/master/python/ray/tune/TuneClient.ipynb>`__.
