Simultaneous Multithreading and Hard Real Time: Can it be Safe? (Artifact)

Abstract

The applicability of Simultaneous Multithreading (SMT) to real-time systems has been hampered by the difficulty of obtaining reliable execution costs in an SMT-enabled system. This problem is addressed from two directions. A scheduler is introduced, CERT-MT, that minimizes SMT-related timing variations, and two new timing analysis methods - one based on the binomial distribution and one based on Cantelli’s Inequality - are given. Both methods estimate probabilistic WCETs and attach statistical confidence levels to those estimates. The timing analyses are applied to tasks executing with and without SMT, and it is found that in some cases, two tasks utilizing SMT can be safely executed in less time than would be needed for either task by itself. A large-scale schedulability study is conducted, showing that CERT-MT can schedule systems with total utilizations twice what could otherwise be achieved. This artifact includes benchmark experiments used to compare execution times with and without SMT and code to analyze the benchmark experiments and duplicate the reported schedulability experiments.