[codes-ross-users] Correlation between latency and number of hops on torus network?

[Daniel Parker]

Hello,

First I wanted to thank Jonathan and Misbah for their help on my last
question. I was successful in setting up networks where arbitrary numbers
of nodes are active or inactive.

Now that I am able to do so, however, I have made a strange observation. It
seems to me that there is not a correlation between the number of hops that
a message must make over a torus network and that message's latency. To
determine this, I created a simple model where one sender and one receiver
node are randomly chosen within a 3D 10x10x10 torus network. I take latency
measurements for 10 pings from the sender to the receiver and back, then
average the values. I repeated this trial 500 times and aggregated the data
into these graphs:

http://imgur.com/a/7rqRw

The first graph shows a cdf of latencies of the different trials, with each
data point color-coded corresponding to the number of hops between the
sender and receiver for that trial. Blue indicates few hops while red
indicates more. The second shows the distribution of hop counts observed
over the 500 trials, with number of hops on the x axis and frequency on the
y axis. As you can see, the latency seems constant despite distance between
the nodes in question, which does not make sense to me. Do any of you know
why this would be? Is there something about the torus implementation that
I'm misunderstanding?

I can upload my code if necessary.

Thanks for your help,

Dan Parker
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.mcs.anl.gov/pipermail/codes-ross-users/attachments/20150723/e7468643/attachment.html>