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Concurrency groups: a new way to look at real-time multiprocessor lock nesting

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Abstract

When designing a real-time multiprocessor locking protocol, the allowance of lock nesting creates complications that can inhibit parallelism. Such protocols are typically designed by focusing on the arbitration of resource requests that should be prohibited from executing concurrently. This paper proposes “concurrency groups,” a new concept that reflects an alternative point of view that focuses instead on requests that can be allowed to execute concurrently. A concurrency group is simply a group of lock requests, determined offline, that can safely execute together. This paper’s main contribution is the CGLP, a new real-time multiprocessor locking protocol that supports lock nesting through the use of concurrency groups. The CGLP is able to reap runtime parallelism benefits that have eluded prior protocols by investing effort offline in the construction of concurrency groups. A schedulability study is presented to quantify these benefits, as well as an approach to determining such groups using an Integer Linear Program (ILP) solver, which we show to be efficient in practice.

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Notes

  1. We assume the use of dynamic group locks (Ward and Anderson 2013), which coalesce all resources a task may require concurrently under a single request. For example, if a task requires access to \({\ell } _a\) and then conditionally requires access to either \({\ell } _b\) or \({\ell } _c\), it issues a single request for \(\{{\ell } _a, {\ell } _b, {\ell } _c\}\).

  2. Note that this work presents a change in the definition of slot from that by Nemitz et al. (2019b).

  3. We use a single MCS lock (Mellor-Crummey and Scott 1991) to protect all resources for the group lock. We leave it to future work to compare to a set of resource-ordered locks.

  4. This ordering refers to the order in which resources must be acquired by a given task, not the order in which requests are satisfied (Dijkstra 1978; Havender 1968).

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Acknowledgements

Work supported by NSF Grants CNS 1409175, CNS 1563845, CNS 1717589, and CPS 1837337, ARO Grant W911NF-17-1-0294, and funding from General Motors. This material is based upon work supported by the National Science Foundation Graduate Research Fellowship Program under Grant No. DGS-1650116. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.

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  1. Department of Computer Science, University of North Carolina at Chapel Hill, 201 S. Columbia St., Chapel Hill, NC, 27599, USA

    Catherine E. Nemitz, Tanya Amert, Manish Goyal & James H. Anderson

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  1. Catherine E. Nemitz
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Correspondence to Catherine E. Nemitz.

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Nemitz, C.E., Amert, T., Goyal, M. et al. Concurrency groups: a new way to look at real-time multiprocessor lock nesting. Real-Time Syst 57, 190–226 (2021). https://doi.org/10.1007/s11241-020-09361-0

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