[Beowulf] MPICH question

Reuti reuti at staff.uni-marburg.de
Tue Feb 22 15:23:41 PST 2005


you are not using shared memory, and so you will also see the rsh tasks. This 
is the usual behavior of mpich (and the other forks are most likely responsible 
for the async network communication between the tasks, although they are just 
on the same machine).

But you try this, and use in addition the following switch to ./configure 
mpich: -comm=shared , recompile (or at least relink) your program, and use a 
machinefile with only one line:


and you we now have only 4 processes and use shared memory.

Cheers - Reuti

Quoting John Lau <cflau at clustertech.com>:

> Hi,
> I have a question on the number of processes spawned by MPICH. I am
> using MPICH --with-device=ch_p4. When I use mpirun -np 4 to
> start a mpi process, total 8 processes will be spawned. But only 4
> processes have loadings on CPUs. I would like to know if it is the
> correct behavior of MPICH? And what's the use of the 4 no-loading
> process? Thank you.
> Best regards,
> John Lau
> -- 
> John Lau Chi Fai
> Cluster Technology Ltd.
> cflau at clustertech.com
> Tel: (852) 2994-3727
> Fax: (852) 2994-2101
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