Newsgroups: comp.parallel.pvm
From: crispin@csd.uwo.ca (Crispin Cowan)
Subject: Re: Timing distributed processes
Organization: Department of Computer Science, University of Western Ontario, London, Ontario, Canada
Date: 23 Aug 1994 18:08:02 GMT
Message-ID: <33ddu2$75k@falcon.ccs.uwo.ca>

In article <33cgu6$t3e@Emerald.Oz.nthu.edu.tw>,
br801512 <br801512@totoro> wrote:
>We want to caculate the time including communication time,too.
>We have two solutions.
>(1):
>   Calling "time()" before and after Sending/Receiving.
>   It gets the turn around time. 
It also includes time that your task was not scheduled because some
other UNIX process was running.

>(2):
>   Construct another receiving function instead of 
>   blocking receive pvm_recv().
...
>        Looping while (pvm_prob(..) is not SUCCESS);
>        pvm_recv(...);
Which artificially increases the CPU load presented by your task.  If
PVM allocates more than one of your tasks to this CPU, it will
drastically alter the timing.

I don't think either of these methods measure a meaningful metric.  You
have to first determine what it is you want to measure, and then devise
a way to instrument it.  What aspect of performance do you want to
measure?  The wall-clock time to complete your task is the most direct
measure of "performance".  Comparing parallel wall-clock time to
sequential wall-clock time gives you speed-up.  Aggregate CPU usage
over the tasks gives you CPU utilization.  If you can get an idle
network of machines, wall clock time minus CPU usage is roughly your
communications time.  Getting your communications time in a non-idle
network is difficult, because it is hard to determine the spread
between the time a message is delivered to a task and the time the task
actually gets to start processing it.

Crispin
-----
Crispin Cowan, CS PhD student, searching for a research position
University of Western Ontario
Phyz-mail:  Middlesex College, MC28-C, London, Ontario, N6A 5B7
E-mail:     crispin@csd.uwo.ca          Voice:  519-661-3342
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