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Distributed FX software correlation

Distributed FX software correlation. Adam Deller Swinburne University/CSIRO Australia Telescope National Facility Supervisors: A/Prof Steven Tingay, Prof Matthew Bailes (Swinburne), Dr John Reynolds (ATNF). Outline. Software vs hardware correlators

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Distributed FX software correlation

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  1. Distributed FX software correlation Adam Deller Swinburne University/CSIRO Australia Telescope National Facility Supervisors: A/Prof Steven Tingay, Prof Matthew Bailes (Swinburne), Dr John Reynolds (ATNF)

  2. Outline • Software vs hardware correlators • Why software (what it does best, and the price you pay) • Current applications • The DiFX architecture • Performance and current status • Conclusions

  3. Software vs Hardware • “Software correlator”: program running on a supercomputer/cluster • Software is unclocked, could be faster or slower than real-time • No channel/integration time restrictions • Floating pt vs int calculations

  4. Why software • Flexibility - can do science that is impossible with hardware correlators • Rapid (and cheap) development • Add-ons MUCH easier in software • Compatibility and expandability • In general, less approximations due to the use of floating point

  5. The price you pay • Because software & hardware not specifically tuned, less computation per $$ hardware • Therefore not useful for EVLA/SKA scale correlators • Running costs (electricity, aircon) may be higher

  6. Current applications/results • New science the software correlator has enabled: • Disk-based LBA (greater bandwidth) • Adding global disk-based antennas to LBA experiments • High time and frequency resolution allowing wide-field imaging • VERY high frequency resolution for pulsar scintillation studies

  7. Baseband data Core 1 DataStream 1 Core 2 DataStream 2 … … Core M DataStream N Visibilities Timerange, destination Source data Master Node The DiFX architecture MPI is used for inter-process communications

  8. Usage in the LBA • PC-EVN recorders give up to 512 Mbps per DAS (x2 at ATNF antennas) • Data is recorded directly to Linux-formatted storage (Apple Xraid) • Disks shipped to Swinburne • Correlated at the Swinburne supercomputer (~300 P4 machines) • Ftp fringe tests and 256 Mbps eVLBI

  9. Performance Real-time LBA @ 1 Gbps (6 stations x 4x64 MHz bands): 100-200 CPUs (circa 2004 P4s)

  10. Current status • Verification via correlator comparison with VLBA completed • Used in production capacity with LBA - complete switch as soon as sufficient disks available • Further development (graphical frontend, FITS-IDI etc) ongoing • Exploring potential for geodesy

  11. Conclusions • Software correlators can be rapidly developed and enable science that cannot be done elsewhere • Perfect for niche/part-time experiments and feasibility tests • Used successfully with the LBA • Early science results encouraging!

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