Mixed Criticality Systems with Varying Context Switch Costs

Robert Ian Davis, Sebastian Altmeyer, Alan Burns

Research output: Contribution to conferencePaperpeer-review


In mixed criticality systems, it is vital to ensure
that there is sufficient separation between tasks of LO- and
HI-criticality applications, so that the behavior or mis-behavior
of the former cannot affect the functional or timing correctness
of the latter. To ensure appropriate spatial isolation, the
memory address spaces and cache use by LO- and HI-criticality
tasks must be distinct. A consequence of this separation is that
the cost of switching between tasks of the same criticality can
be small, whereas the cost of context switching between tasks
of different criticality levels can be much larger. In this paper,
we focus on integrating the differing context switch costs into
fixed priority preemptive scheduling, and the two mixed
criticality scheduling schemes based on it: SMC and AMC. We
derive simple, refined, and multi-set analyses for each scheme.
Further, we show that the refined and multi-set analyses are
not compatible with Audsley’s Optimal Priority Assignment
algorithm, we therefore propose a heuristic priority assignment
policy aimed at reducing the number of high cost context
switches. Our evaluation is grounded in measurements of
context switch times (save and restore costs) from a prototype
implementation of an explicitly managed cache on an FPGA.
The evaluation shows the effectiveness of the derived analyses
and the proposed priority assignment policy.
Original languageEnglish
Number of pages12
Publication statusPublished - 9 Aug 2018
Event24th IEEE Real-Time and Embedded Technology and Applications Symposium -
Duration: 11 Apr 201813 Apr 2018


Conference24th IEEE Real-Time and Embedded Technology and Applications Symposium
Abbreviated titleRTAS 2018

Bibliographical note

Funding Information:
The research in this paper is partially funded by the ESPRC grant, MCCps (EP/K011626/1) and by the NWO Veni Project “The time is now: Timing Verificationfor Safety-Critical Multi-Cores”. EPSRC Research Data Management: No new primary data was created during this study.

Publisher Copyright:
© 2018 IEEE.

Copyright 2019 Elsevier B.V., All rights reserved.


  • real time
  • schedulability analysis
  • mixed criticality
  • context switch
  • Fixed priority
  • Mixed criticality
  • Scheduling
  • Real time
  • Context switch costs

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