Dear Developers,
I have faced a performance degradation on multi-core single processor machine.
Specifically, in the most recent Open MPI v1.8 the initialization and process
startup stage became ~10x slower compared to v1.6.5. In order to measure
timings I have used the following code snippet:
/*-------------------------------------------*/
#include <mpi.h>
int main (int argc, char *argv[]) {
MPI_Init(&argc,&argv);
MPI_Finalize();
return 0;
}
/*-------------------------------------------*/
The execution wall time has been measured in a trivial way by using the 'time'
command, i.e.:
time mpirun -np 2 ./a.out
Below are given averaged timings for both versions on Linux x86_64 (Intel
i7-3630):
Default settings:
1.8 : 0.679 s
1.6.5: 1.041 s
OMPI_MCA_btl=tcp,self:
1.8 : 0.679 s
1.6.5: 0.041 s
The same problem has been detected on Mac OS X v10.9.2.
Here I should stress that others MPI distributions perform as the OpenMPI
v1.6.5 with the TCP byte transfer layer activated.
So, I am wondering whether it is possible to tune v1.8 in order to boost the
startup process? The problem is that during the automatic nightly verification
of our program we usually spawn parallel binaries a thousands of times.
Thank you In advance!
Best regards,
Victor.
