[gmx-users] Issue with regression test.

[Raymond Arter]

Dear All,

I'm building Gromacs 2018.2 and I've run in to a small issue that I would
like feed back on.

One of the regression tests fails with the following entered in to the log
file.

----
Mdrun cannot use the requested (or automatic) number of ranks, retrying
with 8.

Abnormal return value for ' gmx mdrun    -nb cpu   -notunepme >mdrun.out
2>&1' was 1
Retrying mdrun with better settings...

Abnormal return value for ' gmx mdrun -ntmpi 12      -notunepme >mdrun.out
2>&1' was 1
Retrying mdrun with better settings...

Abnormal return value for ' gmx mdrun -ntmpi 6      -notunepme >mdrun.out
2>&1' was -1
FAILED. Check mdrun.out, md.log file(s) in nbnxn_vsite for nbnxn_vsite
Re-running orientation-restraints using CPU-based PME
Re-running pull_geometry_angle using CPU-based PME
Re-running pull_geometry_angle-axis using CPU-based PME
Re-running pull_geometry_dihedral using CPU-based PME
----

However, on the advice of a colleague I run the following command in the
directory:

    gmx mdrun -ntmpi 4 -notunepme

And got the following result:

----
Reading file topol.tpr, VERSION 2018.2 (single precision)
Non-default thread affinity set, disabling internal thread affinity
Can not increase nstlist because verlet-buffer-tolerance is not set or used

Using 4 MPI threads
Using 3 OpenMP threads per tMPI thread

On host ****** 4 GPUs auto-selected for this run.
Mapping of GPU IDs to the 4 GPU tasks in the 4 ranks on this node:
  PP:0,PP:1,PP:2,PP:3

Back Off! I just backed up traj.trr to ./#traj.trr.1#

Back Off! I just backed up ener.edr to ./#ener.edr.1#
starting mdrun 'Protein'
20 steps,      0.1 ps.

step 20 Turning on dynamic load balancing, because the performance loss due
to load imbalance is 3.3 %.

Writing final coordinates.

Back Off! I just backed up confout.gro to ./#confout.gro.1#

 Dynamic load balancing report:
 DLB was turned on during the run due to measured imbalance.
 Average load imbalance: 13.0%.
 The balanceable part of the MD step is 25%, load imbalance is computed
from this.
 Part of the total run time spent waiting due to load imbalance: 3.3%.
 Steps where the load balancing was limited by -rdd, -rcon and/or -dds: X 0
% Y 0 %

NOTE: 6 % of the run time was spent in domain decomposition,
      17 % of the run time was spent in pair search,
      you might want to increase nstlist (this has no effect on accuracy)

               Core t (s)   Wall t (s)        (%)
       Time:        1.932        0.161     1200.0
                 (ns/day)    (hour/ns)
Performance:       56.337        0.426
----

Is this just a problem with the regression test and the build of Gromacs is
fine, or
is there a problem with the build I have done?

Thanks in advance.

R.