[Swift-user] Tuning parameters of coaster execution

[Andriy Fedorov]

Hi,

I am trying to understand how to set correctly the coaster-related
parameters to optimize execution of my workflow. A single task I have
takes around 1-2 minutes. I set maxWalltime to 2 minutes, and there 40
of these tasks in my toy workflow. Coasters are configured as
gt2:gt2:pbs. When I run it with the default parameters, the workflow
completes (this is great!).

Now I am trying to understand what's going on and how to improve the
performance. Looking at the scheduler queue, I see that two jobs are
submitted in the beginning of the execution for 18 min each, one with
1 node, and one with 2 nodes. All of the execution is happening in
these two jobs (the number of jobs submitted is just two, for 40 taks,
so looks like things work). First question: why does it happen this
way? (two jobs, 18 minutes each, specific node allocation) I assume
only one of them (2-node) is executing worker tasks, but in this case
why allocation time is 18 minutes, not 20 (each worker walltime is 2
min)?

Second question: how do I make coaster to request more nodes? I tried
to increase nodeGranularity to 10. This resulted in only one (!) job
with 10 nodes and 20 min walltime showing up on the scheduler. But it
looks like the jobs are still executed 2 at a time!

Progress:  Selecting site:38  Active:2

According to documentation, default workersPerNode=1, so I would
expect at least 10 to be active. Again, I don't understand what's
going on uder the hood....

Can coaster experts give me some guidance what is going on, and how to
intelligently set the parameters?

Thanks!

--
Andriy Fedorov, Ph.D.

Research Fellow
Brigham and Women's Hospital
Harvard Medical School
75 Francis Street
Boston, MA 02115 USA
fedorov at bwh.harvard.edu