This pages page summarizes known problems and troubleshoot information that help running experiments a a MHz rate.

1. Node configurations 

To achieve a MHz rate, we need to consider the following:

• The heavy-lifting SMD0 core (MPI rank 0) needs to be assigned on an individual node exclusively. This will allow the entire node to read smalldata in parallel at the full bandwidth.
• The Srv cores (data writing) should not exceed some limit (currently, we see 8 as the upper limit for data writing cores).

More detail on node types - PSANA2 diagram.

To assign node configurations, run 

#!/bin/bash

#SBATCH --partition=anagpu
#SBATCH --nodes=2
#SBATCH --ntasks-per-node=3
#SBATCH --output=%j.log


# setup node configurations
./setup_nodes.sh


# "-u" flushes print statements which can otherwise be hidden if mpi hangs
# "-m mpi4py.run" allows mpi to exit if one rank has an exception
mpirun python -u -m mpi4py.run /reg/g/psdm/tutorials/examplePython/mpiDataSource.py

2. Open MPI failed to TCP connect

We observe that when running using more than a few nodes (> 20) and that nodes assigned to your job are from mixed pools (cmp, mon, or eb nodes mixed in), jobs may fail with the following message:

--------------------------------------------------------------------------

...

WARNING: Open MPI failed to TCP connect to a peer MPI process.  This

...

should not happen.

...

Your Open MPI job may now hang or fail.

...

  Local host: drp-srcf-eb010

...

  PID:        130465

...

  Message:    connect() to 172.21.164.90:1055

...

 failed
  Error:      Operation now in progress (115)

...

--------------------------------------------------------------------------

This happens because we have multiple interfaces (tcp, ib, etc.) assigned to a node, however some might not have all enabled and that results in no connection when a node is missing that selected interface.

Solution

Prior to running your job, apply either 1) or 2).

1. Restrict to 172.21.164 subnet 

...

export OMPI_MCA_btl_tcp_if_include=172.21.164.90/1072

2. Exclude 172.21.152 subnet

export OMPI_MCA_btl_tcp_if_exclude=eno1

...

2. Node configurations 

...