Specify number of processes for each host in upcxx-run.

[Robert Pierce]

upcxx-run supports independent arguments to control assignment of ranks to hosts: -np to specify the number of ranks per host; -ssh-servers to specify hosts. This works as long as host resources and loads are homogeneous. For inhomogeneous clusters, it would be useful to be able to specify the number of processes for each individual host.

[Dan Bonachea]

Hi Robert, thanks for the suggestion.

In the meantime, you should be able to get the effect you are asking for by specifying host names multiple times, once per process. I know this is not as convenient as what you are asking for, but it should have the same effect.

[Robert Pierce]

That works. Thanks!

[Dan Bonachea]

This was discussed in the 2020-02-12 meeting and deferred indefinitely.

While we agree it would be useful, we currently lack the necessary infrastructure in gasnetrun to deploy such a feature.

However we also noted that (in cases other than GASNet ssh-spawner) launch via underlying spawners can circumvent some of the limitations in upcxx-run. See issue #315