On Thu, Oct 9, 2008 at 10:13 AM, Jeff Squyres <email@example.com>
On Oct 9, 2008, at 8:06 AM, Sangamesh B wrote:
That seems to indicate that something else is going on -- with -np 1, there should be no MPI communication, right? I wonder if the memory allocator performance is coming into play here.
OpenMPI : 120m 6s
MPICH2 : 67m 44s
I'd be more inclined to double-check how the Gromacs app is being compiled in the first place - I wouldn't think the OpenMPI memory allocator would make anywhere near that much difference. Sangamesh, do you know what command line was used to compile both of these? Someone correct me if I'm wrong, but if MPICH2 embeds optimization flags in the 'mpicc' command and OpenMPI does not, then if he's not specifying any optimization flags in the compilation of Gromacs, MPICH2 will pass its embedded ones on to the Gromacs compile and be faster. I'm rusty on my GCC, too, though - does it default to an O2 level, or does it default to no optimizations?
Since the benchmark is readily available, I'll try running it later today.. didn't get a chance last night.