Throttling – Revisited Walter F.J. Müller, GSI, Darmstadt CBM Collaboration Meeting 13 th April 2010

13 April 2010 CBM Collaboration Meeting -- Walter F.J. Müller, GSI 2 Shown on CBM FEE/DAQ Workshop on 23 rd Feb 2010 Behavior under Overload Question: What happens if more data is generated in the FEE ASCIs than can be transported to and processed by the DAQ system ? part of the data all the time Default: Each FEE/ROC drops data independently  Under overload we get part of the data all the time all of the data part the time Goal: All FEE/ROC drop data in a coordinated way  Under overload we get all of the data part the time

13 April 2010 CBM Collaboration Meeting -- Walter F.J. Müller, GSI 3 Proposals Received Global approaches  'throttle-OR'  wfjm Local approaches  1. 'Use drop slots'  R. Szczygiel  2. 'Discard epochs in a prioritized way'  S. Linev  3. 'Delete overhang data at begin of epoch'  P. Fischer  4. 'fixed frame size'  L. Schmidt First summary  local methods clearly preferential to global approaches  method 1+2 handle whole epochs  need a substantial buffer space to work effectively  perfect for later stages  method 3+4 aim to concentrate data losses towards the end of a each epoch  can be implemented on small buffer footprint

13 April 2010 CBM Collaboration Meeting -- Walter F.J. Müller, GSI 4 Canonical Architecture Data not time sorted PreAmp digitization FIFO Readout control, e,g, Token ring Data time sorted

13 April 2010 CBM Collaboration Meeting -- Walter F.J. Müller, GSI 5 Local Throttle Algorithm I PreAmp digitization FIFO Readout control, e,g, Token ring Add a THROTTLE Flip-Flop - set when FIFO full - cleared at epoch Data dropped if FF set Unclear what the system dynamics is !!

13 April 2010 CBM Collaboration Meeting -- Walter F.J. Müller, GSI 6 Local Throttle Algorithm II PreAmp digitization FIFO Readout control, e,g, Token ring Add a hit counter - data dropped if counter > limit - clear counter at epoch This implements 'fixed maximal bandwidth' per channel. Simple, clean, predictable, but potentially not optimal bandwidth usage.

13 April 2010 CBM Collaboration Meeting -- Walter F.J. Müller, GSI 7 Summary This is meant to start the discussion  no pre-mature conclusions at this point This is meant to start the discussion  no pre-mature conclusions at this point Discrete event simulations urgently needed to understand the system dynamics of different approaches Goal:  a system with a benign behavior when operated close to the bandwidth limit despite some beam intensity fluctuations  gradual increase of 'effective dead time'  data stays normalizable Alternative:  Substantial 'safety factor' in all bandwidth estimates...

13 April 2010 CBM Collaboration Meeting -- Walter F.J. Müller, GSI 8 The End Thanks for your attention