[gmx-users] GPU efficiency question

[Albert]

Dear:

  I've got two GTX690 in a a workstation and I found that when I run the 
md production with following two command:

mpirun -np 4 md_run_mpi

or

mpirun -np 2 md_run_mpi

the efficiency are the same..... I notice that gromacs can detect 4 GPU 
(probably because GTX690 have two core..):

4 GPUs detected on host node4:
   #0: NVIDIA GeForce GTX 690, compute cap.: 3.0, ECC:  no, stat: compatible
   #1: NVIDIA GeForce GTX 690, compute cap.: 3.0, ECC:  no, stat: compatible
   #2: NVIDIA GeForce GTX 690, compute cap.: 3.0, ECC:  no, stat: compatible
   #3: NVIDIA GeForce GTX 690, compute cap.: 3.0, ECC:  no, stat: compatible


why the "-np 2" and "-np 4" are the same efficiency? shouldn't it be 
faster for "-np 4" ?

thank you very much

Albert