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Multi-Site VLBI UDP Flow Testing: Challenges and Performance Analysis

This presentation by Dr. Richard Hughes-Jones from The University of Manchester details the setup and findings from multiple VLBI UDP flow tests conducted in December 2006. The tests aimed to evaluate network performance concerning throughput, packet loss, and re-ordering across various international sites, including Onsala, JIVE, and Bologna. Key challenges faced during implementation included firewall configurations, CPU load issues, and routing problems. The results demonstrated varied performance with significant insights into data communication efficiencies.

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Multi-Site VLBI UDP Flow Testing: Challenges and Performance Analysis

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  1. VLBI & Protocolsvlbi_udp Multiple Flow Tests Richard Hughes-Jones The University of Manchesterwww.hep.man.ac.uk/~rich/ then “Talks” ESLEA Bits&Bytes, Manchester, 7-8 Dec 2006, R. Hughes-Jones Manchester

  2. Setting up the Tests • Thank you to the people at all the sites for your help and making facilities available • Including: • Onsala • JIVE • Torun and Pioner Poznan • GARR Bologna • Jodrell and Manchester Network Group • Dante ESLEA Bits&Bytes, Manchester, 7-8 Dec 2006, R. Hughes-Jones Manchester

  3. vlbi_udp: Multi-site Streams Gbit link Chalmers University of Technology, Gothenburg Metsähovi OnsalaSweden Jodrell BankUK Gbit link TorunPoland DedicatedGbit link Dwingeloo DWDM link MedicinaItaly ESLEA Bits&Bytes, Manchester, 7-8 Dec 2006, R. Hughes-Jones Manchester

  4. vlbi_udp: UDP on the WAN • iGrid2002 monolithic code • Convert to use pthreads • control • Data input • Data output • Code branch for Simon’s file transfer tests • Work on vlbi_recv: • Output thread polled for data in the ring buffer – burned CPU • Input thread signals output thread when there is work to do – else wait on semaphore – packet loss at high rate, variable thoughput • Output thread uses sched_yield() when no work to do • Multi-flow Network performance – being set up Nov/Dec06 • 3 Sites to JIVE: manc UKLight; Manc production; Bologna GEANT PoP • Measure: throughput, packet loss, re-ordering, 1-way delay • To do • Add code for:MarkV card and PCEVN interface ESLEA Bits&Bytes, Manchester, 7-8 Dec 2006, R. Hughes-Jones Manchester

  5. vlbi_udp: Some of the Problems • JIVE made Huygens, mark524 (.54) and mark620 (.59) available • Within minutes of Arpad leaving the Alteon NIC of mark524 lost the data network! • OK used mark623 (.62) – faster CPU • Firewalls needed to allow vlbi_udp ports • Aarrgg (!!!) Huygens is SUZE Linux • Routing – well this ALWAYS needs to be fixed !!! • AMD Opteron did not like sched_getaffinity() sched_setaffinity() • Comment out this bit • udpmon flows Onsala to JIVE look good • udpmon flows JIVE mark623 to Onsala & Manc UKL don’t work • Firewall down stops after 77 udpmon loops • Firewall up udpmon cant communicate with Onsala • CPU load issues on the markV systems • Don’t seem to be able to keep up with receiveing UDP flow AND emptying the ring buffer • Torun PC / Link lost during the tests ESLEA Bits&Bytes, Manchester, 7-8 Dec 2006, R. Hughes-Jones Manchester

  6. 2.2GHz AMD Athlon • Udpmon OK but single thread • Vlbi_udp uses recvmsg() & iovectors • No not quite !!! • Asked for a flow of 600Mbit/s (-w20 us) got ~300 Mbit/s (-w58 us) • 1.8% packet loss • 1.1% re-ordered (mainly by 1 or 2 packets) • Onsala gig7 (Academic internet to Ams then UKLight)Onsala  gig8 (all Academic internet) • ~4.5% lost and ~3.5% re-ordered vlbi_udp Onsala  mark623 • It worked ! ESLEA Bits&Bytes, Manchester, 7-8 Dec 2006, R. Hughes-Jones Manchester

  7. Multiple vlbi_udp Flows • Gig7  Huygens UKLight 15 us spacing 800 Mbit/s • Gig8  mark623 Academic Internet 20 us spacing 600 Mbit/s • Bologna  mark620 Academic Internet 30 us spacing 400 Mbit/s SJ5 Access link SURFnet Access link GARR Access link ESLEA Bits&Bytes, Manchester, 7-8 Dec 2006, R. Hughes-Jones Manchester

  8. Multiple vlbi_udp Flows • Gig7  Huygens UKLight 15 us spacing • 816 Mbit/s del <1Mbit/sstep 1 Mbit/s • Zero packet loss • Zero re-ordering • Gig8  mark623 Academic Internet 20 us spacing • 612 Mbit/s • 0.6 falling to 0.05% packet loss • 0.02 % re-ordering • Bologna  mark620 Academic Internet 30 us spacing • 396 Mbit/s • 0.02 % packet loss • 0 % re-ordering ESLEA Bits&Bytes, Manchester, 7-8 Dec 2006, R. Hughes-Jones Manchester

  9. Any Questions? ESLEA Bits&Bytes, Manchester, 7-8 Dec 2006, R. Hughes-Jones Manchester

  10. Backup Slides ESLEA Bits&Bytes, Manchester, 7-8 Dec 2006, R. Hughes-Jones Manchester

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