Dramatic slowdown for -np 2
jharrop at acm.org
Mon Feb 11 21:58:55 PST 2002
This may be an MPI problem, but I'm not sure so I'm posting it here and
We are developing an application on a four node Beowulf while we wait for
the remaining nodes to arrive. Speed-up has been close to predicted with
-np 3 and 4 in a master/slave mode. But when I run at -np 2 the speed
drops to approximately 1/4 of the original serial application. (On 4 nodes
- that is 1 master and 3 slaves, we get about 2.5 times speed-up relative
to the original application.) All runs produce the same answer.
In the MPI code we have basic SEND, RECV, BCAST and REDUCE - nothing
fancy. Does anyone know if any of these or other MPI functions run into
problems with one to one master slave ration? Any other enlightenment
would be welcome.
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