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Upgrade Letter of Intent High Level Trigger Thorsten Kollegger

Upgrade Letter of Intent High Level Trigger Thorsten Kollegger. ALICE | Offline Week | 03.10.2012. Requirements. Focus of ALICE upgrade on physics probes requiring high statistics: sample 10 nb -1 Online System Requirements

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Upgrade Letter of Intent High Level Trigger Thorsten Kollegger

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  1. Upgrade Letter of IntentHigh Level TriggerThorsten Kollegger ALICE | Offline Week | 03.10.2012

  2. Requirements Focus of ALICE upgrade on physics probes requiring high statistics: sample 10 nb-1 Online System Requirements Sample full 50kHz Pb-Pb interaction rate (current limit at ~500Hz, factor 100 increase)  ~1.1 TByte/s detector readoutHowever: storage bandwidth limited to ~20 GByte/s many physics probes have low S/B: classical trigger/event filter approach not efficient ALICE | Offline Week | 03.10.2012 | Thorsten Kollegger

  3. Slide from Karel Safarik • Main physics topics, at the LHC uniquely accessible with the ALICE detector: • measurement of heavy-flavour transport parameters: • diffusion coefficient – azimuthal anisotropy and RAA • in-medium thermalization and hadronization – meson-baryon • mass dependence of energy loss – RAA • study of QGP properties via transport coefficients (h/s, q) • J/y , y’, and cc states down to zero pt in wide rapidity range • yields and transverse momentum spectra – RAA, elliptic flow • density dependence – central vs. forward production • statistical hadronization vs. dissociation/recombination ˆ Physics Motivation ALICE | Offline Week | 03.10.2012 | Thorsten Kollegger

  4. Physics Motivation Slide from Karel Safarik • measurement of low-mass and low-ptdi-leptons • chiral symmetry restoration – vector-meson spectral function • disappearance of vacuum condensate and generation of hadron masses • QGP thermal radiation – low-mass di-lepton continuum • space-time evolution of the QGP – radial and elliptic flow of emitted radiation • Jet quenching and fragmentation • jet energy recuperation at very low pt • heavy-flavourtagged jets, gluon vs. quark induced jets • heavy-flavour produced in fragmentation • particle identified fragmentation functions • Heavy-nuclear states • high statistics mass-4 and -5 (anti-)hypernuclei • search for H-dibaryon, Ln bound state, etc. ALICE | Offline Week | 03.10.2012 | Thorsten Kollegger

  5. Why not triggering? Slide from Luciano Musa Triggering on D0, Ds and Λc (pT>2 Gev/c)  ~ 36 kHz@50kHz rate... ALICE | Offline Week | 03.10.2012 | Thorsten Kollegger

  6. Strategy Data reduction by (partial) online reconstruction and compression Store only reconstruction results, discard raw data Demonstrated with TPC clustering since Pb-Pb 2011 Optimized data structures for lossless compression Algorithms designed to allow for offline reconstruction passes with improved calibrations  Implies much tighter coupling between online and offline reconstruction software ALICE | Offline Week | 03.10.2012 | Thorsten Kollegger

  7. Event Size Expected data sizes for minimum bias Pb-Pb collisions at full LHC energy ALICE | Offline Week | 03.10.2012 | Thorsten Kollegger

  8. TPC Data Reduction First steps up to clustering on FEE/FPNs (RORC FPGA)Further steps require full event reconstruction on EPNs, pattern recognition requires only coarse online calibration ALICE | Offline Week | 03.10.2012 | Thorsten Kollegger

  9. TPC Data Reduction Float to Fixed-Point convertion, size according to detector resolution Reduction of data size/cluster: 22 Byte -> 10 Byte ALICE | Offline Week | 03.10.2012 | Thorsten Kollegger

  10. TPC Data Reduction • Lossless data compression with Huffman code (entropy encoding) • Data members transformed to increase performance: • e.g. Padrow Number => Drow(i) = row(i) – row(i-1) • Entropy reduced from ~6 to 1.1 ALICE | Offline Week | 03.10.2012 | Thorsten Kollegger

  11. TPC Data Reduction Overall data size to tape reduced by factor 4.3 Used in Pb+Pb 2011, p+p 2012... standard ALICE data format Further reduction possible by transforming pad, time coordinates ALICE | Offline Week | 03.10.2012 | Thorsten Kollegger

  12. TPC Data Reduction First steps up to clustering on FEE/FPNs (RORC FPGA)Further steps require full event reconstruction on EPNs, pattern recognition requires only coarse online calibration ALICE | Offline Week | 03.10.2012 | Thorsten Kollegger

  13. Further data reduction • Discard clusters not assigned to tracks (or in the track vincinity) • Requires online calibration (at least coarse one) • Allows later offline re-production • Alternative: identify background clusters ALICE | Offline Week | 03.10.2012 | Thorsten Kollegger

  14. Processing Power Estimate for online systems based on current HLT processing power - ~2500 cores in ~200 nodes 108 FPGAs on H-RORCs for local preprocessing • TPC clusterfinding: 1 FPGA equivalent to ~80 CPU cores - 64 GPGPUs for tracking (NVIDIA GTX480 + GTX580) Scaling to 50 kHz rate to estimate requirements - ~ 250.000 cores additional processing power by FPGAs + GPGPUs 1250-1500 nodes in 2018 with multicores ALICE | Offline Week | 03.10.2012 | Thorsten Kollegger

  15. HLT TPC Tracking Algorithm implemented as multithreaded CPU and CUDA GPU version ALICE | Offline Week | 03.10.2012 | Thorsten Kollegger

  16. HLT TPC Tracking 3-fold speedup of GPU compared to optimized CPU version on 6 cores ALICE | Offline Week | 03.10.2012 | Thorsten Kollegger

  17. HLT Tracking Performance Active GPU Threads using Dynamic Scheduling time Consistency between GPU and CPU version of tracker threads Active GPU Threads: 67% ALICE | Offline Week | 03.10.2012 | Thorsten Kollegger

  18. HLT Tracking Performance Old HLT efficiency macro • Efficiency/Clone/Fake rate calculation • merged with PWG-PP/TPC code • Under review by TPC group ALICE | Offline Week | 03.10.2012 | Thorsten Kollegger

  19. Summary After the upgrade: Store only reconstruction results, discard raw data Requires online calibration Algorithms designed to allow for offline reconstruction passes with improved calibrations  Implies much tighter coupling between online and offline reconstruction software ALICE | Offline Week | 03.10.2012 | Thorsten Kollegger

  20. ALICE | Offline Week | 03.10.2012 | Thorsten Kollegger

  21. Backup - Processing Power Estimate of processing power based on scaling by Moore’s law However: no increase in single core clock speed, instead multi/many-core Reconstruction software needs to adapt to full use resources Picture from Herb Sutte: The Free Lunch Is Over A Fundamental Turn Toward Concurrency in Software Dr. Dobb's Journal, 30(3), March 2005 (updated) ALICE | Offline Week | 03.10.2012 | Thorsten Kollegger

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