[gmx-users] Fwd: Bad performance in free energy calulations

Julian Zachmann FrankJulian.Zachmann at uab.cat
Tue May 19 15:13:27 CEST 2015

```Dear Gromacs users,

I want to do free energy calculations following this
<http://www.bevanlab.biochem.vt.edu/Pages/Personal/justin/gmx-tutorials/free_energy/index.html>
tutorial.
My system contains a GPCR, membrane, small ligand, solvate - in total
60.000 atoms. I want to perturb the ligand (31 atoms, 3 hydrogen atoms get
converted to dummy atoms, one carbon atom get converted to a carbon atom,
the other 27 ligand atoms just change slightly their charges). Apart from
the perturbation and an extra simulated annealing step in the
equilibration, I am following the tutorial as close as possible.

My calculations work, but the computer performance is really bad. I am
using only 8 processors for each Lambda, so domain decomposition is not
really an issue (see below) but the CPUs run with only 25% load. Which
could be the reason? Any ideas?

.

Thank you very much for your help!!

Julian

D O M A I N   D E C O M P O S I T I O N   S T A T I S T I C S

av. #atoms communicated per step for force:  2 x 74451.3
av. #atoms communicated per step for LINCS:  2 x 4495.3

Part of the total run time spent waiting due to load imbalance: 1.4 %
Steps where the load balancing was limited by -rdd, -rcon and/or -dds: X 2
%

R E A L   C Y C L E   A N D   T I M E   A C C O U N T I N G

On 8 MPI ranks

Computing:          Num   Num      Call    Wall time         Giga-Cycles
Ranks Threads  Count      (s)         total sum    %
-----------------------------------------------------------------------------
Domain decomp.         8    1        150       3.136         65.226   0.3
DD comm. load          8    1        150       0.208          4.335   0.0
DD comm. bounds        8    1        150       0.257          5.355   0.0
Neighbor search        8    1        151      11.329        235.608   1.2
Comm. coord.           8    1       4850      11.368        236.425   1.2
Force                  8    1       5001     466.392       9699.934  50.6
Wait + Comm. F         8    1       5001      10.598        220.418   1.2
PME mesh               8    1       5001     386.976       8048.244  42.0
NB X/F buffer ops.     8    1      14701       1.670         34.724   0.2
Write traj.            8    1          3       0.133          2.768   0.0
Update                 8    1       5001       1.474         30.664   0.2
Constraints            8    1      10002      20.387        423.998   2.2
Comm. energies         8    1        501       2.255         46.891   0.2
Rest                                           4.983        103.631   0.5
-----------------------------------------------------------------------------
Total                                        921.165      19158.221 100.0
-----------------------------------------------------------------------------
Breakdown of PME mesh computation
-----------------------------------------------------------------------------
PME redist. X/F        8    1      15003     134.013       2787.183  14.5
PME spread/gather      8    1      20004     179.277       3728.576  19.5
PME 3D-FFT             8    1      20004      22.603        470.092   2.5
PME 3D-FFT Comm.       8    1      20004      47.072        979.004   5.1
PME solve Elec         8    1      10002       3.941         81.965   0.4
-----------------------------------------------------------------------------

Core t (s)   Wall t (s)        (%)
Time:     3693.315      921.165      400.9
(ns/day)    (hour/ns)
Performance:        0.938       25.583
Finished mdrun on rank 0 Tue May 19 14:01:45 2015
```