Using GPUs for training models in the cloud

Graphics Processing Units (GPUs) can significantly accelerate the training process for many deep learning models. Training models for tasks like image classification, video analysis, and natural language processing involves compute-intensive matrix multiplication and other operations that can take advantage of a GPU's massively parallel architecture.

Training a deep learning model that involves intensive compute tasks on extremely large datasets can take days to run on a single processor. However, if you design your program to offload those tasks to one or more GPUs, you can reduce training time to hours instead of days.

Before you begin

Cloud Machine Learning Engine lets you run any TensorFlow training application on a GPU- enabled machine. Read the TensorFlow guide to using GPUs and the section below on assigning ops to GPUs to ensure your application makes use of available GPUs.

Some models don't benefit from running on GPUs. We recommend GPUs for large, complex models that have many mathematical operations. Even then, you should test the benefit of GPU support by running a small sample of your data through training.

Requesting GPU-enabled machines

To use GPUs in the cloud, configure your training job to access GPU-enabled machines:

  • Set the scale tier to CUSTOM.
  • Configure each task (master, worker, or parameter server) to use one of the GPU-enabled machine types below, based on the number of GPUs and the type of accelerator required for your task:
    • standard_gpu: A single NVIDIA Tesla K80 GPU
    • complex_model_m_gpu: Four NVIDIA Tesla K80 GPUs
    • complex_model_l_gpu: Eight NVIDIA Tesla K80 GPUs
    • standard_p100: A single NVIDIA Tesla P100 GPU
    • complex_model_m_p100: Four NVIDIA Tesla P100 GPUs
    • standard_v100: A single NVIDIA Tesla V100 GPU (Beta)
    • large_model_v100: A single NVIDIA Tesla V100 GPU (Beta)
    • complex_model_m_v100: Four NVIDIA Tesla V100 GPUs (Beta)
    • complex_model_l_v100: Eight NVIDIA Tesla V100 GPUs (Beta)

Below is an example of submitting the job using the gcloud command.

Alternatively, if you are learning how to use Cloud ML Engine or experimenting with GPU-enabled machines, you can set the scale tier to BASIC_GPU to get a single worker instance with a single NVIDIA Tesla K80 GPU.

See more information about comparing machine types.

In addition, you need to run your job in a region that supports GPUs. The following regions currently provide access to GPUs:

  • us-east1
  • us-central1
  • us-west1
  • asia-east1
  • europe-west1
  • europe-west4

To fully understand the available regions for Cloud ML Engine services, including model training and online/batch prediction, read the guide to regions.

Submitting the training job

You can submit your training job using the gcloud ml-engine jobs submit training command.

  1. Define a config.yaml file that describes the GPU options you want. The structure of the YAML file represents the Job resource. For example:

    trainingInput:
      scaleTier: CUSTOM
      masterType: complex_model_m_gpu
      workerType: complex_model_m_gpu
      parameterServerType: large_model
      workerCount: 9
      parameterServerCount: 3
    
  2. Use the gcloud command to submit the job, including a --config argument pointing to your config.yaml file. The following example assumes you've set up environment variables, indicated by a $ sign followed by capital letters, for the values of some arguments:

    gcloud ml-engine jobs submit training $JOB_NAME \
            --package-path $APP_PACKAGE_PATH \
            --module-name $MAIN_APP_MODULE \
            --job-dir $JOB_DIR \
            --region us-central1 \
            --config config.yaml \
            -- \
            --user_arg_1 value_1 \
             ...
            --user_arg_n value_n
    

Notes:

  • If you specify an option both in your configuration file (config.yaml) and as a command-line flag, the value on the command line overrides the value in the configuration file.
  • The empty -- flag marks the end of the gcloud specific flags and the start of the USER_ARGS that you want to pass to your application.
  • Flags specific to Cloud ML Engine, such as --module-name, --runtime-version, and --job-dir, must come before the empty -- flag. The Cloud ML Engine service interprets these flags.
  • The --job-dir flag, if specified, must come before the empty -- flag, because Cloud ML Engine uses the --job-dir to validate the path.
  • Your application must handle the --job-dir flag too, if specified. Even though the flag comes before the empty --, the --job-dir is also passed to your application as a command-line flag.
  • You can define as many USER_ARGS as you need. Cloud ML Engine passes --user_first_arg, --user_second_arg, and so on, through to your application.

For more details of the job submission options, see the guide to starting a training job.

Assigning ops to GPUs

To make use of the GPUs on a machine, make the appropriate changes to your TensorFlow training application:

  • High-level Estimator API: No code changes are necessary as long as your ClusterSpec is configured properly. If a cluster is a mixture of CPUs and GPUs, map the ps job name to the CPUs and the worker job name to the GPUs.

  • Core Tensorflow API: You must assign ops to run on GPU-enabled machines. This process is the same as using GPUs with TensorFlow locally. You can use tf.train.replica_device_setter to assign ops to devices.

When you assign a GPU-enabled machine to a Cloud ML Engine process, that process has exclusive access to that machine's GPUs; you can't share the GPUs of a single machine in your cluster among multiple processes. The process corresponds to the distributed TensorFlow task in your cluster specification. The distributed TensorFlow documentation describes cluster specifications and tasks.

GPU device strings

A standard_gpu machine's single GPU is identified as "/gpu:0". Machines with multiple GPUs use identifiers starting with "/gpu:0", then "/gpu:1", and so on. For example, complex_model_m_gpu machines have four GPUs identified as "/gpu:0" through "/gpu:3".

Python packages on GPU-enabled machines

GPU-enabled machines come pre-installed with tensorflow-gpu, the Tensorflow Python package with GPU support. See the Cloud ML Runtime Version List for a list of all pre-installed packages.

Maintenance events

If you use GPUs in your training jobs, be aware that the underlying virtual machines will occasionally be subject to Compute Engine host maintenance. The GPU-enabled virtual machines used in your training jobs are configured to automatically restart after such maintenance events, but you may have to do some extra work to ensure that your job is resilient to these shutdowns. Configure your training application to regularly save model checkpoints (usually along the Cloud Storage path you specify through the --job-dir argument to gcloud ml-engine jobs submit training) and to restore the most recent checkpoint in the case that a checkpoint already exists.

The TensorFlow Estimator API implements this functionality for you, so if your model is already wrapped in an Estimator, you do not have to worry about maintenance events on your GPU workers.

If it is not feasible for you to wrap your model in a TensorFlow Estimator and you want your GPU-enabled training jobs to be resilient to maintenance events, you must write the checkpoint saving and restoration functionality into your model manually. TensorFlow does provide some useful resources for such an implementation in the tf.train module - specifically, tf.train.checkpoint_exists and tf.train.latest_checkpoint.

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