Notes from April 2014 maintenance

This note summarizes the results of maintenance across the entire ExoGENI Testbed in April 2014.

The highlights

  • Minor fixes added to BEN to better support inter-domain topologies
  • UDP performance issue addressed. See below for more details.
  • FOAM updated across the racks
  • Floodlight updated across the racks
  • Connectivity
    • most of the connectivity caveats from the previous note still apply.
    • UvA rack is currently not reachable. We suspect a problem with the configuration in SURFnet, which we will address.
      • This behavior appears to have resolved itself by 05/06 without our intervention. Please report any further problems. 

The details: UDP performance

Some of you have observed very poor performance for UDP transfers – extremely high packet losses and very low transfer rates. This issue was traced to three separate causes:

  • Poor implementation of “learning switch” functionality in the version of Floodlight OpenFlow controller we were using. It resulted in sudden losses of packets after a period of time, particularly between bare-metal nodes. To resolve this issue we upgraded Floodlight to version 0.9 and replaced the “learning switch” module in it with a better-behaved “forwarding” module.
  • Insufficient configuration of the QEMU interface to the guest VM, which resulted in very high packet losses. We updated the Quantum agent to support the proper options.
  • Sensitivity of UDP transfers to host- and guest-side transmit and receive buffers. We tuned the host-side buffers on worker nodes, however the tuning guest-side must be accomplished by the experimenter.

To explain further how to get the best performance out of UDP on ExoGENI we will publish a separate blog entry in the immediate future.

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