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Experiences Using Web100 for Visible Human Testbeds

Experiences Using Web100 for Visible Human Testbeds. Thomas Hacker Center for Advanced Computing, University of Michigan Brian Athey Michigan Center for Biological Information, University of Michigan Web100 Evaluator’s Workshop Boulder, CO August 1, 2002. Outline. Visible Human Project

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Experiences Using Web100 for Visible Human Testbeds

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  1. Experiences Using Web100 for Visible Human Testbeds Thomas Hacker Center for Advanced Computing, University of Michigan Brian Athey Michigan Center for Biological Information, University of Michigan Web100 Evaluator’s Workshop Boulder, CO August 1, 2002

  2. Outline • Visible Human Project • Edgewarp Visualization Application • Performance Problems • Tuning Methodology • Results • Conclustion

  3. Visible Human Project • Sponsored by the National Library of Medicine • Goal is to deliver rendered images of anatomic content to teaching stations in the anatomy lab • Scaling requirements are stringent • At least 40 teaching stations per lab • Simultaneous access by teaching centers across the nation

  4. Edgewarp • Core component of the Visible Human Project content delivery • Designed and developed by Dr. Fred Bookstein and Dr. William Green • Delivers “filmstrip” fly-thorough of anatomical data • Allows students to navigate freely through anatomical data

  5. Edgewarp Data Access • Edgewarp pulls image voxels from data server • Only the voxels necessary to draw the current image in detail are pulled • Successively higher resolution voxels are pulled as the image fills in • Allows fast navigation (low-res) • Provides high resolution still images

  6. Performance Problems • U-M VHP demonstration at NASA AMES Gigabit Ethernet Workshop in August, 2000 • End-to-end TCP performance from University of Michigan to NASA AMES was around 3 Mb/sec. • Network bottleneck was OC-12! • No clear cause for performance problems

  7. Web100 • Tuning Methodology developed in collaboration with PSC staff (Matt Mathis) • Used Web100 as TCP “oscilloscope” to guide tuning efforts • Methodology • Start with the wire • Work up to TCP • Finish with the application

  8. Pre-tuning • Transmission test performed from PSC Visible Human Server to University of Michigan • Edgewarp test rig used with voxel server • Initial throughput approximately 12 Mb/sec • Network bottleneck was 100 Mb/sec link at University of Michigan

  9. Pre-tuning • Web100 showed small receiver socket buffers, little packet loss, poor throughput

  10. Tuning Methodology • Start with the wire • Used Cat-5e cabling • Used good network adapters • No congestion losses reported by Network Operations website • Network adaters in full-duplex mode

  11. Tuning Methodology • Work up to TCP • Client host tuned to support SACK, MTU discovery, Timestamps, and Window Scaling • The TCP maximum and default send and receive socket buffer set to 2 MB • The server was checked to ensure that these options were enabled.

  12. Web100 Reality Check Check settings in Web100 to make sure they take effect

  13. Check tcpdump to Make Sure… # /usr/sbin/tcpdump port 8694 Kernel filter, protocol ALL, datagram packet socket tcpdump: listening on all devices 19:07:26.172433 eth1 > spbuild.engin.umich.edu.1088 > vh.psc.edu.8694: S 1067517561:1067517561(0) win 32758 <mss 1460,sackOK,timestamp 29833739 0,nop,wscale 5> (DF) 19:07:26.192439 eth1 < vh.psc.edu.8694 > spbuild.engin.umich.edu.1088: S 1021853801:1021853801(0) ack 1067517562 win 4060 <mss 1460,sackOK,timestamp 1073113995 29833739,nop,wscale 5> (DF)

  14. Results • Web100 indicated “sawtooth” transmission behavior, higher throughput, and packet loss

  15. Results • Throughput improved by about a factor of four

  16. Conclusion • Web100 is an effective tool for diagnosing TCP performance problems • Web100 is an essential aid in tuning • Web100 helps to close the “wizard gap” necessary to improve performance

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