[gmx-users] condition on MPI and GPU tasks

[Sikandar Mashayak]

Hi,

I am checking out GPU performance of Gromacs5.0 on a single node of a
cluster.
The node has two 8-core Sandy Bridge Xeon E5-2670 and two NVIDIA K20x GPUs.

My question - is there a restriction on how many number of MPI tasks can be
used per GPU task?

I observe that I could only perform mdrun with same number of MPI tasks as
GPU tasks. I use one OpenMP thread per MPI task. If I use more MPI tasks
than no. of GPUs, I get an error:


Fatal error:
Incorrect launch configuration: mismatching number of PP MPI processes and
GPUs per node.
mdrun_mpi was started with 4 PP MPI processes per node, but you provided 2
GPUs.

Thanks,
Sikandar