Atomo: Communication-efficient Learning via Atomic Sparsification

This repository contains source code for Atomo, a general framework for atomic sparsification of stochastic gradients. Please check the full paper for detailed information about this project.

Overview:

ATOMO is a general framework for atomic sparsification of stochastic gradients. Given a gradient, an atomic decomposition, and a sparsity budget, ATOMO gives a random unbiased sparsification of the atoms minimizing variance. ATOMO sets up and optimally solves a meta-optimization that minimizes the variance of the sparsified gradient, subject to the constraints that it is sparse on the atomic basis, and also is an unbiased estimator of the input.

Depdendencies:

Tested stable depdencises:

• python 2.7 (Anaconda)
• PyTorch 0.3.0 (please note that, we're moving to PyTorch 0.4.0, and 1.0.x)
• torchvision 0.1.18
• MPI4Py 0.3.0
• python-blosc 1.5.0

We highly recommend installing an Anaconda environment. You will get a high-quality BLAS library (MKL) and you get a controlled compiler version regardless of your Linux distro.

We provide this script to help you with building all dependencies. To do that you can run:

bash ./tools/pre_run.sh

Cluster Setup:

For running on distributed cluster, the first thing you need do is to launch AWS EC2 instances.

Launching Instances:

This script helps you to launch EC2 instances automatically, but before running this script, you should follow the instruction to setup AWS CLI on your local machine. After that, please edit this part in ./tools/pytorch_ec2.py

cfg = Cfg({
    "name" : "PS_PYTORCH",      # Unique name for this specific configuration
    "key_name": "NameOfKeyFile",          # Necessary to ssh into created instances
    # Cluster topology
    "n_masters" : 1,                      # Should always be 1
    "n_workers" : 8,
    "num_replicas_to_aggregate" : "8", # deprecated, not necessary
    "method" : "spot",
    # Region speficiation
    "region" : "us-west-2",
    "availability_zone" : "us-west-2b",
    # Machine type - instance type configuration.
    "master_type" : "m4.2xlarge",
    "worker_type" : "m4.2xlarge",
    # please only use this AMI for pytorch
    "image_id": "ami-xxxxxxxx",            # id of AMI
    # Launch specifications
    "spot_price" : "0.15",                 # Has to be a string
    # SSH configuration
    "ssh_username" : "ubuntu",            # For sshing. E.G: ssh ssh_username@hostname
    "path_to_keyfile" : "/dir/to/NameOfKeyFile.pem",

    # NFS configuration
    # To set up these values, go to Services > ElasticFileSystem > Create new filesystem, and follow the directions.
    #"nfs_ip_address" : "172.31.3.173",         # us-west-2c
    #"nfs_ip_address" : "172.31.35.0",          # us-west-2a
    "nfs_ip_address" : "172.31.14.225",          # us-west-2b
    "nfs_mount_point" : "/home/ubuntu/shared",       # NFS base dir

For setting everything up on EC2 cluster, the easiest way is to setup one machine and create an AMI. Then use the AMI id for image_id in pytorch_ec2.py. Then, launch EC2 instances by running

python ./tools/pytorch_ec2.py launch

After all launched instances are ready (this may take a while), getting private ips of instances by

python ./tools/pytorch_ec2.py get_hosts

this will write ips into a file named hosts_address, which looks like

172.31.16.226 (${PS_IP})
172.31.27.245
172.31.29.131
172.31.18.108
172.31.18.174
172.31.17.228
172.31.16.25
172.31.30.61
172.31.29.30

After generating the hosts_address of all EC2 instances, running the following command will copy your keyfile to the parameter server (PS) instance whose address is always the first one in hosts_address. local_script.sh will also do some basic configurations e.g. clone this git repo

bash ./tool/local_script.sh ${PS_IP}

SSH related:

At this stage, you should ssh to the PS instance and all operation should happen on PS. In PS setting, PS should be able to ssh to any compute node, this part dose the job for you by running (after ssh to the PS)

bash ./tools/remote_script.sh

Prepare Datasets

We currently support MNIST and Cifar10 datasets. Download, split, and transform datasets by (and ./tools/remote_script.sh dose this for you)

bash ./src/data_prepare.sh

Job Launching

Since this project is built on MPI, tasks are required to be launched by PS (or master) instance. run_pytorch.sh wraps job-launching process up. Commonly used options (arguments) are listed as following:

Argument	Comments
n	Number of processes (size of cluster) e.g. if we have P compute node and 1 PS, n=P+1.
hostfile	A directory to the file that contains Private IPs of every node in the cluster, we use hosts_address here as mentioned before.
lr	Inital learning rate that will be use.
momentum	Value of momentum that will be use.
network	Types of deep neural nets, currently LeNet, ResNet-18/32/50/110/152, and VGGs are supported.
dataset	Datasets use for training.
batch-size	Batch size for optimization algorithms.
test-batch-size	Batch size used during model evaluation.
comm-type	A fake parameter, please always set it to be Bcast.
num-aggregate	Number of gradients required for the PS to aggregate.
max-steps	The maximum number of iterations to train.
svd-rank	The expected rank of gradients ATOMO used (which is the same as the sparsity budget s in our paper).
epochs	The maximal number of epochs to train (somehow redundant).
eval-freq	Frequency of iterations to evaluation the model.
enable-gpu	Training on CPU/GPU, if CPU please leave this argument empty.
train-dir	Directory to save model checkpoints for evaluation.

Model Evaluation

Distributed evaluator will fetch model checkpoints from the shared directory and evaluate model on validation set. To evaluate model, you can run

bash ./src/evaluate_pytorch.sh

with specified arguments.

Evaluation arguments are listed as following:

Argument	Comments
eval-batch-size	Batch size (on validation set) used during model evaluation.
eval-freq	Frequency of iterations to evaluation the model, should be set to the same value as run_pytorch.sh.
network	Types of deep neural nets, should be set to the same value as run_pytorch.sh.
dataset	Datasets use for training, should be set to the same value as run_pytorch.sh.
model-dir	Directory to save model checkpoints for evaluation, should be set to the same value as run_pytorch.sh.

Future Work

Those are potential directions we are actively working on, stay tuned!

• Explore the use of Atomo with Fourier decompositions, due to its utility and prevalence in signal processing.
• Examine how we can sparsify and compress gradients in a joint fashion to further reduce communication costs.
• Explore jointly sparsification of the SVD and and its singular vectors.
• Integrate ATOMO to state-of-the-art PS (or distributed) frameworks e.g. Ray.

Citation

@inproceedings{wang2018atomo,
  title={ATOMO: Communication-efficient Learning via Atomic Sparsification},
  author={Wang, Hongyi and Sievert, Scott and Liu, Shengchao and Charles, Zachary and Papailiopoulos, Dimitris and Wright, Stephen},
  booktitle={Advances in Neural Information Processing Systems},
  pages={9871--9882},
  year={2018}
}