This page includes examples for Open MPI that use
horovodrun. Check your MPI documentation for arguments to the
command on your system.
Typically one GPU will be allocated per process, so if a server has 4 GPUs, you would run 4 processes. In
the number of processes is specified with the
To run on a machine with 4 GPUs:
$ horovodrun -np 4 -H localhost:4 python train.py
To run on 4 machines with 4 GPUs each:
$ horovodrun -np 16 -H server1:4,server2:4,server3:4,server4:4 python train.py
Failures due to SSH issues
The host where
horovodrun is executed must be able to SSH to all other hosts without any prompts.
horovodrun fails with permission error, verify that you can ssh to every other server without entering a password or
answering questions like this:
The authenticity of host '<hostname> (<ip address>)' can't be established.
RSA key fingerprint is xx:xx:xx:xx:xx:xx:xx:xx:xx:xx:xx:xx:xx:xx:xx:xx.
Are you sure you want to continue connecting (yes/no)?
To learn more about setting up passwordless authentication, see this page.
The authenticity of host '<hostname> (<ip address>)' can't be established prompts, add all the hosts to
~/.ssh/known_hosts file using
$ ssh-keyscan -t rsa,dsa server1 server2 > ~/.ssh/known_hosts