On the reliability of hardware event monitors in MPSoCs for critical domains

Performance Monitoring Units (PMUs) are at the heart of most-advanced timing analysis techniques to control and bound the impact of contention in Commercial Off-The-Shelf (COTS) SoCs with shared resources (e.g. GPUs and multicore CPUs). In this paper, we report discrepancies on the values obtained from the PMU event monitors and the number of events expected based on PMU event description in the processor's official documentation. Discrepancies, which may be either due to actual errors or inaccurate specifications, make PMU readings unreliable. This is particularly problematic in consideration of the critical role played by event monitors for timing analysis in domains such as automotive and avionics. This paper proposes a systematic procedure for event monitor validation. We apply it to validate event monitors in the NVIDIA Xavier and TX2, and the Zynq UltraScale+ MPSoC. We show that, while some event monitors count as expected, this is not the case for others whose discrepancies with expected values we analyze.
This work has been partially supported by the Spanish Ministry of Economy and Competitiveness (MINECO) under grant TIN2015-65316-P, the SELENE European Union’s Horizon 2020 (H2020) research and innovation programme under grant agreement No 871467, and the HiPEAC Network of Excellence. MINECO partially supported Jaume Abella under Ramon y Cajal postdoctoral fellowship (RYC-2013-14717), Enrico Mezzetti under Juan de la-Cierva-Incorporacion postdoctoral fellowship (IJCI-2016-27396), and Leonidas Kosmidis under Juan de la Cierva-Formacion postdoctoral fellowship (FJCI-2017-34095).
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