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Future Dataflow Bottlenecks

Future Dataflow Bottlenecks. Christopher O’Grady with A. Perazzo and M. Weaver Babar Dataflow Group. View of the DAQ System. A series of parallel assembly lines System runs as fast as the slowest worker on the assembly line

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Future Dataflow Bottlenecks

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  1. Future Dataflow Bottlenecks Christopher O’Grady with A. Perazzo and M. Weaver Babar Dataflow Group

  2. View of the DAQ System • A series of parallel assembly lines • System runs as fast as the slowest worker on the assembly line • Trigger rate projections tell us how fast workers should work, event size projections tell us how fast they actually take. • Use software written by Amedeo Perazzo and James Swain to record system performance info • We use this information to project into the future. All the following plots are made by Matt Weaver.

  3. Projections • On June 25, 2001 I predicted the DCH readout would be a bottleneck in 2005. • Also, when we saw unexplained deadtime from GLT, the projection system “told” us that there was 90us delay shipping data (which we then saw on the scope). • This projection system works well.

  4. Projection Improvements • Matt has split all occupancy projections into HER/LER/LUM components (previously, only for DCH). • Using Jan 2004 background runs. • Looks at all ROMs individually. Previously just the worst. • Projecting through 2007-2010 (3*10**34)

  5. General Observations • HER worse than 2002 • LER better than 2002 • Now see a luminosity term in sizes • Event size is 75kb in 2007 (3*10**34)

  6. Trigger Rate Projections • From the Trigger Group: • Need <140us!

  7. Fiber Transfer Bottlenecks • DCH/SVT the largest. GLT also important. 140us

  8. Behaviour of Fiber Deadtime • Worse than other deadtime, since “earliest” buffering in the system.

  9. Plan of Attack for Fiber • DCH: in progress • GLT/DCT: sudong in progress, should be straightforward • SVT: • try running system at 60MHz, or • reduce occupancy (and efficiency) with thresholds • EMT: straightforward

  10. Feature Extraction Bottleneck DCH/DRC/EMC/EMT/SVT ideally need work 140us

  11. Plan of Attack for FEX • DCH FEX taken care of with electronics upgrade. • DRC and SVT FEX relatively easy (don’t “do” anything). • EMT FEX requires data format change (some work but doable, in principle). Amedeo already did one pass. • EMC FEX hard! Already a lot of work on that by Matt.

  12. EMC FEX • Need new idea (like Walt had) or new CPUs. • new CPUs won't necessarily work easily: mechanical, electrical, software issues. significant work and money. • Maybe 20% gain from nbr bits, but hardware untested and corners may not see gain.

  13. VME Bottleneck Currently overestimated. EMC/DRC/SVT 140us

  14. Plan of Attack for VME • Many bottlenecks, but maybe not a problem. • Could imagine going to all-network event build. • For this would likely need ~150 Gbit network cards ($45K) + fibers + network switch ($60K?). Maybe more L3 nodes.

  15. Summary • Up until now have been able to reduce big bottlenecks: EMT FEX, EMC FEX, network stack, DCH data transfer(in progress), GLT/DCT data transfer (sudong, in progress). • With the above work we should be able to sustain 5kHz in 2007. Not good enough for predicted 7kHz L1. • EMC FEX and SVT fiber transfer hardest. • Bottlenecks getting varied and difficult: ~$100K + significant code mods to eliminate VME. ~$500K for new CPUs, and new CPUs may be tough. • There are deadtime periods we don’t quantitatively understand.

  16. My Intuition • It’s going to be a little rough by 2007. • Continue improving the system piece by piece with manpower and money we have, BUT • Tightening the trigger in 2007 will likely be necessary.

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