[gmx-users] Re: GROMACS + MOSIX

Mikko Huhtala mhuhtala at abo.fi
Wed Apr 17 14:40:43 CEST 2002

David van der Spoel writes:
 > On Wed, 17 Apr 2002, Alan Wilter Sousa da Silva wrote:
 > >1- Unfortunately you can *cheat* LAM-MPI (or MPICH).
 > Or do you  mean fortunately?
 > >2- MOSIX and LAM-MPI (or MPICH) can co-exist in the same cluster.
 > >
 > >	If run a parallel job with MPI, MOSIX gets knowing and so it try
 > >balance the load although it can migrate MPI procs, so it just avoid that
 > >procs that MPI is requiring.
 > Any special tricks to get it going? It might be of interest to more 
 > people.

(open)Mosix cannot currently migrate (multithreaded) processes that
use shared memory, although there is work being done to that end, if I
have understood correctly.

We are running LAM and Gromacs on an openMosix cluster. LAM processes
are distributed the usual way via rsh, and the rsh server process is
run locked to its node on all but the cluster login node. This way the
LAM processes are not migrated (children of the login process inherit
the migratability), although I'm not sure how necessary this is: MPI
communicates via sockets, which Mosix cannot migrate, so Mosix will
try to keep the processes on the same node with the sockets even if
migration is allowed. 

Mosix will balance everything else that _is_ allowed to migrate and
work around the load of the MPI processes.

Migratable sockets are also on the to-do list of the openMosix
project, I think.


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