Newsgroups: comp.parallel.mpi
From: ramesh@chippewa.ERC.MsState.Edu (Ramesh Pankajakshan)
Subject: Re: Performance problems using mpi on the SGI Power Challenge
Organization: MSU/NSF Engineering Research Center
Date: 20 Sep 1996 18:54:48 GMT
Message-ID: <RAMESH.96Sep20135448@chippewa.ERC.MsState.Edu>

I have had similiar problems on our SGI Power Challenge(12 R10Ks, 4 Gig).
It seems that when the load is greater than the number of available
processors the message passing performance degrades dramatically. Eg.
One of my codes typically spends 5% of the runtime in communications on
an unloaded machine. But with 16 heavy processes running on the machine
the communication time goes to 60% of runtime ! This is inspite of the
fact that total runtime is higher due to processor, bus and memory contention.


Ramesh
--
Ramesh Pankajakshan

