Hi,
I am running an MPI program where N processes write to a single file on a
single shared memory machine.
I’m using OpenMPI v.4.0.2.
Each MPI process write a 1MB chunk of data for 1K times sequentially.
There is no overlap in the file between any of the two MPI processes.
I ran the program for -np = {1, 2, 4, 8}.
I am seeing that the speed of the collective write to a file for -np = {2,
4, 8} never exceeds the speed of -np = {1}.
I did the experiment with a few different file systems {local disk, ram
disk, Luster FS}.
For all of them, I see similar results.
The speed of collective write to a single shared file never exceeds the
speed of single MPI process case.
Any tip or suggestions?
I used MPI_File_write_at() routine with proper offset for each MPI process.
(I also tried MPI_File_write_at_all() routine, which makes the performance
worse as np gets bigger.)
Before writing, MPI_Barrrier() is used.
The start time is taken right after MPI_Barrier() using MPI_Timer();
The end time is taken right after another MPI_Barrier().
The speed of the collective write is calculate as
(total data amount written to the file)/(time between the first
MPI_Barrier() and the second MPI_Barrier());
Any idea to increase the speed?
Thanks,
David
