perfSONAR User Q&A and Other Discussion

[Eli Dart <>]

On 10/16/13 9:46 AM, Alan Whinery wrote:
> You might also reveal something useful by using periodic reports in your
> bwctl invocations (like " -i 1 ") you may find that the per second
> reports show burstiness, or the lack of it.

I find this to be very very helpful.

There is a big difference between a clean ramp to a stable speed, and 
wild fluctuation that is averaged.

A clean ramp to a stable speed argues against the presence of packet 
loss.  If performance is poor but stable, I would check the hosts and 
the application, and then check for a clean bottleneck link.  Wild 
fluctuation points toward loss - check your router and switch buffers. 
(And if "poor but stable" means fluctuating between 10Kbps and 30Kbps, 
there is probably loss too :)

None of this is set in stone of course.  However, I find that telling 
bwctl to give periodic reports is very helpful indeed.

                --eli


> On 10/16/2013 6:26 AM, Wefel, Paul wrote:
> > Couple ideas
> >
> > Run owamp between these two hosts looking for packet loss in only one
> > direction.
> > Check the switch interface that Dst is connected to looking for queue
> > drops and pause frames being sent.
> >
> > I have also seen strange issues with some NICS when offloading is enabled
> > on them.
> >
> > good luck, let us know what you find.
> >
> > -paul
> > NCSA @ UIUC
> >
> > -----Original Message-----
> > From: Roderick Mooi 
> > <>
> > Date: Wednesday, October 16, 2013 5:07 AM
> > To: 
> > ""
> > <>,
> >  
> > ""
> > <>
> > Subject: [perfsonar-user] Help with inconsistent bwctl measurements
> >
> > > Hi
> > >
> > > I have been trying to locate the cause of inconsistent measurements
> > > between two nodes for a few weeks now without success. The pattern I'm
> > > seeing is available at:
> > >
> > > https://192.96.2.247/serviceTest/bandwidthGraph.cgi?url=http://localhost:8
> > > 085/perfSONAR_PS/services/pSB&key=d9013ce7df20b8bbe45defeaeae785d6&keyR=0a
> > > 0ed6c928edf28976414a2cc7e87d6f&dstIP=192.96.2.247&srcIP=196.21.48.249&dst=
> > > 192.96.2.247&src=perfsonara.sanren.ac.za&type=TCP&length=2592000
> > >
> > > Src-Dst is consistent but Dst-Src is not.
> > >
> > > Manual tests (attached) show the same behaviour without any indication of
> > > cause - measures 941 Mbps then drops to 189 Mbps (end) and back to 941
> > > (nothing different in the logs between "good" measurements and "bad"
> > > ones). The only time I've seen something similar is when I was testing
> > >from a 10 G interface to a 1 G interface which was subsequently being
> > > flooded. In this case both interfaces are 1 G. I'm also not seeing any
> > > problems with measurements along the path or between these nodes and any
> > > other nodes. Additionally, there is very little (< 50 Mbps) real traffic
> > > between these 2 nodes.
> > >
> > > Any ideas?
> > >
> > > Thanks!
> > >
> > > Roderick
> > >
> > > --
> > > Roderick Mooi      | SANREN Engineer
> > > --
> > >
> > >  | +27 12 841 4111 | www.sanren.ac.za
> > >
> > >
> > >
> > >
> > > --
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--
Eli Dart, Network Engineer                          NOC: (510) 486-7600
ESnet Office of the CTO (AS293)                          (800) 333-7638
Lawrence Berkeley National Laboratory
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