Fast and Correct Load-Link/Store-Conditional Instruction Handling in DBT Systems

Martin Kristien, Tom Spink, Brian Campbell, Susmit Sarkar, Ian Stark, Bjoern Franke, Igor Boehm, Nigel Topham

Research output: Contribution to journalArticlepeer-review

Abstract

Dynamic Binary Translation (DBT) requires the implementation of load-link/store-conditional (LL/SC) primitives for guest systems that rely on this form of synchronization. When targeting e.g. x86 host systems, LL/SC guest instructions are typically emulated using atomic Compare-and-Swap (CAS) instructions on the host. Whilst this direct mapping is efficient, this approach is problematic due to subtle differences between LL/SC and CAS semantics. In this paper, we demonstrate that this is a real problem, and we provide code examples that fail to execute correctly on QEMU and a commercial DBT system, which both use the CAS approach to LL/SC emulation. We then develop two novel and provably correct LL/SC emulation schemes: (1) A purely software based scheme, which uses the DBT system’s page translation cache for correctly selecting between fast, but unsynchronized, and slow, but fully synchronized memory accesses, and (2) a hardware accelerated scheme that leverages hardware transactional memory (HTM) provided by the host. We have implemented these two schemes in the Synopsys DesignWare® ARC® nSIM DBT system, and we evaluate our implementations against full applications, and targeted micro-benchmarks. We demonstrate that our novel schemes are not only correct, but also deliver competitive performance on-par or better than the widely used, but broken CAS scheme.
Original languageEnglish
Pages (from-to)3544 - 3554
Number of pages11
JournalIEEE Transactions on Computer-Aided Design of Integrated Circuits and Systems
Volume39
Issue number11
Early online date2 Oct 2020
DOIs
Publication statusPublished - 1 Nov 2020
Event2020 International Conference on Compilers, Architecture, and Synthesis for Embedded Systems -
Duration: 20 Sep 202025 Sep 2020
http://esweek.hosting2.acm.org/cases/

Keywords

  • Parallel architectures
  • platform virtualization

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