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MathGroup Archive 2001

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ParallelMap inefficient?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg27290] ParallelMap inefficient?
  • From: Mike Yukish <may106 at psu.edu>
  • Date: Fri, 16 Feb 2001 03:58:54 -0500 (EST)
  • Organization: Penn State University, Center for Academic Computing
  • Sender: owner-wri-mathgroup at wolfram.com

Hello,

I am starting to use the parallel programming toolbox, and I've found
the ParallelMap[ ] function to be essentially broken, most likely due to
some sort of comm glitch. I was curious if anyone else has experienced a
similar problem, or if it is just my network.

If I run the following commands (listtt is a 5 element list of real
numbers), with one remote server active...

x1=SessionTime[];
ParallelMap[Sin,listtt]
SessionTime[]-x1

It takes 5-7 seconds. This is to connect with a slave computer that is
sharing a hub with the master. Obviously something is wrong. By
contrast, if I define the function on the slave

maparoni[x_]:=Map[Sin,x]

and do the following...

Do[
  With[{x=listtt},RemoteEvaluate[maparoni[x]]  ]   ,     {20}   ]
SessionTime[]-x1

It only takes 5 seconds. Note the difference. I am executing the Sin[ ]
function twenty times more, I am passing discrete hunks of data twenty
times more, and I am passing twenty times the total amount of data, yet
it takes less time to complete. So the basic linking between computers
appears to work OK.

Anybody else have experience with the ParallelMap[ ] function? I see
similar performance with ParallelTable[ ]



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