[Beowulf] ethernet switch, dhcp question

Mark Hahn hahn at physics.mcmaster.ca
Mon Oct 4 21:53:04 PDT 2004

> run several programs but the performance seems a little slow.  All 
> the computers in my lab are connected directly to the campus 
> network.  Would I see an increase in performance if I instead had 
> slaves connected through a switch in my room connected to a master 
> computer using dhcp to assign ip's?

possibly - I think you should ssh to your slaves and look at 
/proc/loadavg while running the MPI program.  (actually, 
I usually run "vmstat 1" on slaves, since it aggregates lots of 
other potentially valuable information.)

if your network is a bottleneck, slaves will be not-fully-busy.
if your campus network is 10 or 100bT or not full-duplex,
that's very likely the case.  if your campus net is gigabit,
then I would be surprised to see much improvement by using 
a local switch (assuming your lab machines are plugged into 
the same campus-owned switch).

if your lab machines are not all equivalent in speed, or if your 
MPI problem is not well-balanced, I'd expect to see some nodes 
busy and others not.  similarly, if there are pesky users running
netscape on some nodes, that's probably going to hurt (assuming 
your code is fairly tight-coupled.)

regards, mark hahn.

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