Latency and throughput of online processing in Soft X-Ray GEM-based measurement system

Abstract

The paper presents latency and performance study of the monitoring system for plasma impurities radiation in a tokamak. The developed solution measures radiation in Soft X-Ray range and can provide valuable information about the ongoing experiment with low latency. This work presents the test configuration with a single-dimensional pixel topology, with 64 channels, tested at photon rate about 100 kHz per channel. The hardware consists of the GEM-based detector, FPGAs, PCIe transmission system and the computer system with 64-bit x86 architecture. The software is the C/C++ code optimized for the execution time and working in the global trigger mode. The system uses raw data acquisition and the backend computations in CPU to provide high accuracy and high-quality results, not easily achievable otherwise. The research includes measurements of the throughput of the system and the latency of the whole data path - between the pulse detection in FPGA and storing of spectroscopy histograms in the file system in memory. The direction of improvements and further development were proposed.

International Journal of Electronics and Telecommunications

“…IV. FUTURE WORKS With new triggering modes available, there is need to fully test throughput and latency of computing platform/data path with data download only and with algorithms in online mode as done in earlier work for global triggering mode [9], [11]. Currently access to control modules and log files are available in different WWW services.…”

“…If the computation will be too slow system can temporarily, at some point, reject data packets (early architecture of the solution is presented in more details in [6]). 10 ms latency of data computation in global triggering mode was achieved and available throughputs were tested and presented in [11]. Similar tests are pending for other triggering modes, where lower latency and bigger throughput (in terms of significant data) on the same bandwidth should be achieved.…”

“…• data layout in memory -not optimal for CPU calculations, preventing zero-copy solution (needed double buffering), additional data preparation needed • data from all channels is send -not all channels provide valuable X-ray related data Despite described inefficiencies system can process data with latency less than 10ms (more details in [11]).…”

Soft real-time data processing solutions in measurement systems on example of small-scale GEM based x-ray spectrometer

“…Measurement of hardware throughput is presented in [59]. Tests of global trigger mode, raw data acquisition, data dispatching, and processing with X-ray spectrogram generation (time, charge, and position) are shown in [60]. Latency, given maximal throughput, was measured and found to be below 10ms.…”

International Journal of Electronics and Telecommunications

“…The data is transmitted without any change to the measurement PC for further postprocessing in Matlab software. More details about data handling in scope of DQM mode can be found in [10]. This mode is also very valuable for further postprocessing algorithms, especially is scope of the charge computation.…”