[mpich-discuss] Program uses 100% with MPICH2 (<10% with MPICH1)

[asco developer]

Hello,

I have a compile C program where communication between process is
implemented using MPI (more precisely MPICH1). In 2005 this seemed to
be a good option and I have kept using this version until today.

Recently a user of the program (free software hosted on
sourceforge.net) tried MPICH2 and reported huge CPU usage. I tried
myself with both version mpich2-1.4.1p1 and mpich2-1.5b2 and I got the
same results. The binary (compiled C code on Linux) uses 100% CPU and
run slowly. Interesting for me it is the fact that if I renice the
process to the lowest possible priority, the performance with MPICH2
gets similar to the MPICH1 counterpart. This puzzles me as with this
result I do know not where to start looking.

Before start posting lots information, possible not really the one you
would need, I ask for your suggestions on what type of information do
you need from my side. The master node sends about 100 MPI_DOUBLE to 1
slave (100/n for n slaves) and little information is printed on
stdout. Each one of the slave processes then executes another binary
external program via the C "system" function call. I have looked
around and I have found this entry in the discussion list,
http://lists.mcs.anl.gov/pipermail/mpich-discuss/2011-January/008787.html,
but I'm not sure if it applies to me, and Hydra is not using CPU, my
program is.


Regards,
João Ramos