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

[Mubarak, Misbah]

Thanks Dan. Keep us posted.

From: Daniel Parker <dkparker at uchicago.edu<mailto:dkparker at uchicago.edu>>
Date: Thursday, July 23, 2015 at 6:02 PM
To: Misbah Mubarak <mmubarak at anl.gov<mailto:mmubarak at anl.gov>>
Subject: Re: [codes-ross-users] Correlation between latency and number of hops on torus network?

Hey Misbah,

So when I ran a "cleaned up" version of my code, the problem didn't occur, so it looks like it's probably something I can find. I'm investigating further and will let you know about the result.

On Thu, Jul 23, 2015 at 3:40 PM, Daniel Parker <dkparker at uchicago.edu<mailto:dkparker at uchicago.edu>> wrote:
Okay, I will try to clean it up for you and send it. Thank you!

On Thu, Jul 23, 2015 at 2:19 PM, Mubarak, Misbah <mmubarak at anl.gov<mailto:mmubarak at anl.gov>> wrote:
Thanks for the update, Dan. If you can share your torus config file (and code, if you have made modifications), I can take a quick peek and may be able to help you out.

From: <codes-ross-users-bounces at lists.mcs.anl.gov<mailto:codes-ross-users-bounces at lists.mcs.anl.gov>> on behalf of Daniel Parker <dkparker at uchicago.edu<mailto:dkparker at uchicago.edu>>
Date: Thursday, July 23, 2015 at 2:46 PM
To: "codes-ross-users at lists.mcs.anl.gov<mailto:codes-ross-users at lists.mcs.anl.gov>" <codes-ross-users at lists.mcs.anl.gov<mailto:codes-ross-users at lists.mcs.anl.gov>>
Subject: [codes-ross-users] Correlation between latency and number of hops on torus network?

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


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