Network Charteristics and Applications

Scott Shealy sshealy at asgnet.psc.sc.edu
Fri Jan 4 16:21:39 EST 2002


I know the question I am about to ask has the usual answer "It depends" .... 
but I was hoping that some people could answer with some specific experiences.

The Question... Which specific parallel applications/algorithms/problem 
classes benefit significantly from bandwidth increases,decreased network 
latency or a combination of both?

I am trying to classify applications/algorithms/problem classes by wether 
they would benefit significantly from network upgrades with the following 
options

	100MB switched running TCP/IP
	n channel-bonded 100MB switched running TCP/IP
	Gigabit ethernet switched running TCP/IP
	Myrinet.

I know the first three solutions don't offer much in the way of latency 
improvements.  So..  
Which  applications/algorithms/problem classes scale no matter what.?
Which applications/algorithms/problem classes scale with increased bandwidth?
Which applications/algorithms/problem classes scale with decreased latency?
Which applications/algorithms/problem classes scale with decreased latency 
and increased bandwidth?

I have read alot of theory on this and read a bunch of stuff by 
Foster..etc.... and can make statements like an application that uses 
frequent short messages will benefit from a lower latency network.  I can 
write formulas that use Tc and Ts and pull out ratios out the wazoo... But I 
am looking for real world applications that people have experience with and 
can share details with or infer some of the ratios for me...


Also if you know of applications/algorithms/problem classes that don't scale 
at all that would be of interest too...  

Also if anyone knows a general reference that discusses this... that would be 
of great interest too.

Thanks for any experience you are willing to share...
Scott Shealy
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