On 11/10/2011 5:19 AM, Jeff Squyres wrote:
On Nov 10, 2011, at 8:11 AM, Mudassar Majeed wrote:
Thank you for your reply. I am implementing a load balancing function for MPI,
that will balance the computation load and the communication both at a time. So
my algorithm assumes that all the cores may at the end get different number of
processes to run.
Are you talking about over-subscribing cores? I.e., putting more than 1 MPI
process on each core?
In general, that's not a good idea.
In the beginning (before that function will be called), each core will have
equal number of processes. So I am thinking either to start more processes on
each core (than needed) and run my function for load balancing and then block
the remaining processes (on each core). In this way I will be able to achieve
different number of processes per core.
Open MPI spins aggressively looking for network progress. For example, if you
block in an MPI_RECV waiting for a message, Open MPI is actively banging on the
CPU looking for network progress. Because of this (and other reasons), you
probably do not want to over-subscribe your processors (meaning: you probably
don't want to put more than 1 process per core).
Or, introduce your own MPI_Test/sleep loop if you really feel that you
otherwise want to oversubscribe. Watch out for pitfalls.
