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From: rfinch@caldwr.water.ca.gov (Ralph Finch)
Newsgroups: comp.sys.isis
Subject: How to measure message overhead
Keywords: message, overhead
Message-ID: <196@locke.water.ca.gov>
Date: 10 Jul 90 15:10:33 GMT
Organization: Calif. Dept. of Water Resources, Sac.
Lines: 32


We have 2 Fortran applications here that we wish to run in a
distributed fashion for faster elapsed times.  The first, a
calibration program, will run from 30 minutes to a few hours for each
server job.  Thus the overhead incurred by running under ISIS and
transferring data across the network in messages is not a problem.  In
the second application, though, each server will probably run perhaps
a few tens of milliseconds, and thus we want to keep overhead as low
as possible.

The overhead model I am assuming is something like

O=f+cB

where O is the total overhead, say in milliseconds
f is a fixed overhead incurred with each message (bcast or reply)
c a coefficient, milliseconds/byte
B the number of bytes transferred in each message

Questions:

1) Is the above model anywhere close to reality?

2) What's a good way of measuring overhead?

2) What have others done to reduce overhead?  I have some ideas, most
from the ISIS manual, but am curious as to what non-obvious things
people have done.
-- 
Ralph Finch			916-445-0088
rfinch@water.ca.gov		...ucbvax!ucdavis!caldwr!rfinch
Any opinions expressed are my own; they do not represent the DWR