Distributed Training

The t2t-trainer supports both synchronous and asynchronous distributed training.

Note that it is almost always more efficient to train on a single machine with multiple GPUs/TPUs. Async training is less stable than sync training, and sync training is much faster on 1 machine than on multiple. For these reasons, we almost always train on single machines with multiple GPUs/TPUs.

T2T uses TensorFlow Estimators and so distributed training is configured with the TF_CONFIG environment variable that is read by the RunConfig along with a set of flags that T2T uses to distribute the computation.

Shared output directory

When using multiple machines, it is necessary that all nodes use the same --output_dir, which means that it should be set to a Google Cloud Storage bucket (gs://...) or a directory on a shared network filesystem.

Utility to produce `TF_CONFIG` and flags

t2t-make-tf-configs generates the TF_CONFIG json strings and the necessary command-line flags for the jobs.

Given a set of master and parameter server addresses, the script outputs, for each job, a line with the TF_CONFIG environment variable and the command-line flags necessary for distributed training. For each job, you should invoke the t2t-trainer with the TF_CONFIG value and flags that are output.

Eval jobs

Eval jobs should set the following flags and do not need the TF_CONFIG environment variable to be set as the eval jobs run locally and do not communicate to the other jobs (the eval jobs read the model checkpoints that the trainer writes out):

--schedule=continuous_eval_on_train_data or --schedule=continuous_eval (for dev data)
--worker_job='/job:localhost'
--output_dir=$TRAIN_DIR

Note that evaluation does not work distributed. That is, distributed jobs should always use --schedule=train.

Examples

Sync training across multiple workers

In this scenario, you wish to do synchronous training across multiple workers. Note that it is easier to simply use 1 worker with multiple GPUs and set --worker_gpu=8, but there may be cases where you may want to have multiple machines.

You will need 1 ip:port for the master and then 1 ip:port for each worker.

For this example we'll use 2 workers and these addresses:

# Master
10.0.0.1:5555

# Worker 1
10.0.0.2:5555

# Worker 2
10.0.0.3:5555

Next we generate the TF_CONFIG and command-line-flags for each job.

$ t2t-make-tf-configs --masters='10.0.0.1:5555' --ps='10.0.0.2:5555,10.0.0.3:5555'
Assuming SYNC distributed training with a single master and 2 workers
'{"cluster": {"master": ["10.0.0.1:5555"], "ps": ["10.0.0.2:5555", "10.0.0.3:5555"]}, "environment": "cloud", "task": {"index": 0, "type": "master"}}'      --master=grpc://10.0.0.1:5555 --ps_replicas=2 --worker_replicas=1 --worker_gpu=0 --worker_id=0 --ps_gpu=1 --sync --schedule=train --worker_job='/job:master'
'{"cluster": {"master": ["10.0.0.1:5555"], "ps": ["10.0.0.2:5555", "10.0.0.3:5555"]}, "environment": "cloud", "task": {"index": 0, "type": "ps"}}'  --schedule=run_std_server
'{"cluster": {"master": ["10.0.0.1:5555"], "ps": ["10.0.0.2:5555", "10.0.0.3:5555"]}, "environment": "cloud", "task": {"index": 1, "type": "ps"}}'  --schedule=run_std_server

The output here is 1 line per job. Each line contains the TF_CONFIG to set for that job as well as the command-line flags to set for that job.

It is a bit confusing that the workers are being passed to the --ps flag, but this is correct. When running in --sync mode, the ps are actually the workers. You can see in the next example below that when --sync=False, i.e. async mode, that the ps are in fact being used as parameter servers.

Here's how we would start each job on their respective machines (the commands below assume that you're ssh'd into that job's machine):

Master:

$ export TF_CONFIG='{"cluster": {"master": ["10.0.0.1:5555"], "ps": ["10.0.0.2:5555", "10.0.0.3:5555"]}, "environment": "cloud", "task": {"index": 0, "type": "master"}}'
$ t2t-trainer \
    --master=grpc://10.0.0.1:5555 \
    --ps_replicas=2 \
    --worker_replicas=1 \
    --worker_gpu=0 \
    --worker_id=0 \
    --ps_gpu=1 \
    --sync \
    --schedule=train \
    --worker_job='/job:master' \
    --model=transformer \
    --hparams_set=transformer_base \
    --problem=translate_ende_wmt32k

Worker 1:

$ export TF_CONFIG='{"cluster": {"master": ["10.0.0.1:5555"], "ps": ["10.0.0.2:5555", "10.0.0.3:5555"]}, "environment": "cloud", "task": {"index": 0, "type": "ps"}}'
$ t2t-trainer --schedule=run_std_server

Worker 2:

$ export TF_CONFIG='{"cluster": {"master": ["10.0.0.1:5555"], "ps": ["10.0.0.2:5555", "10.0.0.3:5555"]}, "environment": "cloud", "task": {"index": 1, "type": "ps"}}'
$ t2t-trainer --schedule=run_std_server

Note that if you have more than 1 GPU on each worker machine, make sure to modify the --ps_gpu passed to the master.

Async training across multiple workers

In this scenario, you wish to do asynchronous training across multiple workers with 1+ shared parameter servers.

Note that async training is usually less stable than sync training and for that reason we almost always prefer sync training, but there may be cases where you want to do async distributed training.

For this example we'll use 2 workers and 2 parameter servers:

# Worker 1
10.0.0.1:5555

# Worker 2
10.0.0.2:5555

# PS 1
10.0.0.3:5555

# PS 2
10.0.0.4:5555

Next we generate the TF_CONFIG and command-line-flags for each job.

$ t2t-make-tf-configs --masters='10.0.0.1:5555,10.0.0.2:5555' --ps='10.0.0.3:5555,10.0.0.4:5555'
Assuming ASYNC distributed training with 2 workers and 2 parameter servers
'{"task": {"index": 0, "type": "chief"}, "cluster": {"chief": ["10.0.0.1:5555"], "ps": ["10.0.0.3:5555", "10.0.0.4:5555"], "worker": ["10.0.0.2:5555"]}, "environment": "cloud"}' --master=grpc://10.0.0.1:5555 --ps_replicas=2 --worker_replicas=2 --worker_gpu=1 --worker_id=0 --ps_gpu=0  --schedule=train --worker_job='/job:chief'
'{"task": {"index": 0, "type": "worker"}, "cluster": {"chief": ["10.0.0.1:5555"], "ps": ["10.0.0.3:5555", "10.0.0.4:5555"], "worker": ["10.0.0.2:5555"]}, "environment": "cloud"}'        --master=grpc://10.0.0.2:5555 --ps_replicas=2 --worker_replicas=2 --worker_gpu=1 --worker_id=1 --ps_gpu=0 --schedule=train --worker_job='/job:worker'
'{"task": {"index": 0, "type": "ps"}, "cluster": {"chief": ["10.0.0.1:5555"], "ps": ["10.0.0.3:5555", "10.0.0.4:5555"], "worker": ["10.0.0.2:5555"]}, "environment": "cloud"}'    --schedule=run_std_server
'{"task": {"index": 1, "type": "ps"}, "cluster": {"chief": ["10.0.0.1:5555"], "ps": ["10.0.0.3:5555", "10.0.0.4:5555"], "worker": ["10.0.0.2:5555"]}, "environment": "cloud"}'    --schedule=run_std_server

Here's how we would start each job on their respective machines (the commands below assume that you're ssh'd into that job's machine):

Worker 1:

$ export TF_CONFIG='{"task": {"index": 0, "type": "chief"}, "cluster": {"chief": ["10.0.0.1:5555"], "ps": ["10.0.0.3:5555", "10.0.0.4:5555"], "worker": ["10.0.0.2:5555"]}, "environment": "cloud"}'
$ t2t-trainer \
    --master=grpc://10.0.0.1:5555 \
    --ps_replicas=2 \
    --worker_replicas=2 \
    --worker_gpu=1 \
    --worker_id=0 \
    --ps_gpu=0 \
    --schedule=train \
    --worker_job='/job:chief' \
    --model=transformer \
    --hparams_set=transformer_base \
    --problem=translate_ende_wmt32k

Worker 2:

$ export TF_CONFIG='{"task": {"index": 0, "type": "worker"}, "cluster": {"chief": ["10.0.0.1:5555"], "ps": ["10.0.0.3:5555", "10.0.0.4:5555"], "worker": ["10.0.0.2:5555"]}, "environment": "cloud"}'
$ t2t-trainer \
    --master=grpc://10.0.0.2:5555 \
    --ps_replicas=2 \
    --worker_replicas=2 \
    --worker_gpu=1 \
    --worker_id=1 \
    --ps_gpu=0 \
    --schedule=train \
    --worker_job='/job:worker' \
    --model=transformer \
    --hparams_set=transformer_base \
    --problem=translate_ende_wmt32k

PS 1:

$ export TF_CONFIG='{"task": {"index": 0, "type": "ps"}, "cluster": {"chief": ["10.0.0.1:5555"], "ps": ["10.0.0.3:5555", "10.0.0.4:5555"], "worker": ["10.0.0.2:5555"]}, "environment": "cloud"}'
$ t2t-trainer --schedule=run_std_server

PS 2:

$ export TF_CONFIG='{"task": {"index": 1, "type": "ps"}, "cluster": {"chief": ["10.0.0.1:5555"], "ps": ["10.0.0.3:5555", "10.0.0.4:5555"], "worker": ["10.0.0.2:5555"]}, "environment": "cloud"}'
$ t2t-trainer --schedule=run_std_server

Increase --worker_gpu on each of the workers if you have multiple GPUs. If the parameter servers are also using GPUs, set --ps_gpu to the number of GPUs on the parameter servers.

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