Improved HLT Framework for Belle II Experiment

Abstract

The original Belle II HLT framework was formally upgraded replacing the old IPC based ring buffer with the ZeroMQ data transport to overcome the unexpected IPC locking problem. The new framework has been working stably in the beam run so far, but it lacks the capability to recover the processing fault without stopping the on-going data taking. In addition, the compatibility with the offline framework (basf2) was lost which was maintained in the original. In order to solve these, an improved core processing framework is developed based on original basf2, while keeping the existing ZeroMQ data transport between the servers unchanged. A new core framework zmq-basf2 is developed with a lock-free 1-to-N and N-to-1 data transport using the ZeroMQ IPC socket so that it keeps a 100% compatibility with the original ring-buffer based framework. When a processing fault occurs, the affected faulty event is salvaged from the input buffer and sent directly to the output using the ZeroMQ broadcast. The terminated process is automatically restarted without stopping data taking. This contribution describes the detail of the improved Belle II HLT framework with the result of the performance test in the real Belle II DAQ data flow.