PVM and MOSIX

Andreas Boklund andreas at amy.udd.htu.se
Wed Nov 1 03:18:20 EST 2000


I have a cluster that use both PVM and MOSIX.
And i used it to run PVMPov.

If MOSIX is much faster i would recommend that you to make sure that
PVMPov really utilizes both machines. Otherwise it could be a
configuration error.


Alternative explanation:

To see what was best i invoked several PVMPov processes, ither on one node
each OR all on the master node and left it to MOSIX to distribute them.

What i noticed was that on 2 nodes the time was almost identical at about
70  seconds. 

Here is a shorter version of my chart:
(read of a graph and rounded, but i think you get the general idea)


Processes 	 Seconds for
		PVM	MOSIX
2		70	70
4		15	35
6		12	40
8		10	45
10		5	45
12		<5	45
14		<5	50
16		<5	55
18		<5	65
20		<5	60

As you notice the PVM times decreased with the number of nodes, while the
MOSIX timing first went down and then up again. The reason for this is
that The computer has to become "overloaded" before MOSIX starts to
migrate processes and when you start many processes the master node get so
overloaded that it cant serve the processes that it has migrated with new
figures to crunch(well it moves them back fills em up and then sends them
away again). Therefor the increase in time with a higher number of
processes. We did find that if we used a larger image then skyvase, the
initial down dip spanned over more processors. This was because the extra
time is in the initial stage before the system has stabilized(all
processes have been migrated).
 

As i see it there shouldnt be any possibility that MOSIX would distribute 
the PVMPov processes better then PVMpov alone. 


Good luck
//Andreas Boklund


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