Simultaneous Multithreading and Hard Real Time: Can It Be Safe?

Authors Sims Hill Osborne, James H. Anderson

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Sims Hill Osborne
  • University of North Carolina, Chapel Hill, NC, USA
James H. Anderson
  • University of North Carolina, Chapel Hill, NC, USA


We thank Prof. Alex Mills (Zicklin School of Business, Baruch College, New York, NY) for reviewing an early draft and offering suggestions, particularly with regards to Sec. 4. We thank Joshua Bakita (UNC-Chapel Hill) for contributions to the code used to execute our benchmark tests. Finally, we thank our anonymous reviewers and Shepherd for the improvements they suggested to the final version of this paper.

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Sims Hill Osborne and James H. Anderson. Simultaneous Multithreading and Hard Real Time: Can It Be Safe?. In 32nd Euromicro Conference on Real-Time Systems (ECRTS 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 165, pp. 14:1-14:25, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)


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 by introducing a scheduling framework, called CERT-MT, that combines scheduling-aware timing analysis with a cyclic-executive scheduler in a way that minimizes SMT-related timing variations. The proposed scheduling-aware timing analysis is based on maximum observed execution times and accounts for the uncertainty inherent in measurement-based timing analysis. The timing analysis is found to work for tasks with and without SMT, though some adjustments are required in the former case. A large-scale schedulability study is presented that shows CERT-MT can schedule systems with total utilizations approaching 1.4 times the core count, without sacrificing safety.

Subject Classification

ACM Subject Classification
  • Computer systems organization → Real-time systems
  • Computer systems organization → Real-time system specification
  • Software and its engineering → Scheduling
  • Hardware → Statistical timing analysis
  • Software and its engineering → Multithreading
  • real-time systems
  • simultaneous multithreading
  • hard real-time
  • scheduling algorithms
  • probability
  • statistics
  • timing analysis


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