Carl G. Ritson

Multicore scheduling for lightweight communicating processes

Process-oriented programming is a design methodology in which software applications are constructed from communicating concurrent processes. A typical process-oriented design involves the composition of a large number of small isolated component processes. These concurrent components allow for the scalable parallel execution of the resulting application on both shared-memory and distributed-memory architectures. In this paper we present a runtime designed to support process-oriented programming by providing lightweight processes and communication primitives. The runtimes scheduler, implemented using lock-free algorithms, automatically executes concurrent components in parallel on multicore systems. Heuristics dynamically group processes into cache-affine work units based on communication patterns. Work units are then distributed via wait-free work-stealing. Initial performance analysis shows that, using the algorithms presented in this paper, process-oriented software can execute with an efficiency approaching that of optimised sequential and coarse-grain threaded designs.

Multicore Scheduling for Lightweight Communicating Processes

Process-oriented programming is a design methodology in which software applications are constructed from communicating concurrent processes. A process-oriented design is typically composed of a large number of small isolated concurrent components. These components allow for the scalable parallel execution of the resulting application on both shared-memory and distributed-memory architectures. In this paper we present a runtime designed to support process-oriented programming by providing lightweight processes and communication primitives. Our runtime scheduler, implemented using lock-free algorithms, automatically executes concurrent components in parallel on multicore systems. Run-time heuristics dynamically group processes into cache-affine work units based on communication patterns. Work units are then distributed via wait-free work-stealing. Initial performance analysis shows that, using the algorithms presented in this paper, process-oriented software can execute with an efficiency approaching that of optimised sequential and coarse-grain threaded designs.

Exploring garbage collection with haswell hardware transactional memory

Intels latest processor microarchitecture, Haswell, adds support for a restricted form of transactional memory to the x86 programming model. We explore how this can be applied to three garbage collection scenarios in Jikes RVM: parallel copying, concurrent copying and bitmap marking. We demonstrate gains in concurrent copying speed over traditional synchronisation mechanisms of 48-101%. We also show how similar but portable performance gains can be achieved through software transactional memory techniques. We identify the architectural overhead of capturing sufficient work for transactional execution as a major stumbling block to the effective use of transactions in the other scenarios.

Benchmarking weak memory models

To achieve good multi-core performance, modern microprocessors have weak memory models, rather than enforce sequential consistency. This gives the programmer a wide scope for choosing exactly how to implement various aspects of inter-thread communication through the systems shared memory. However, these choices come with both semantic and performance consequences, often in tension with each other. In this paper, we focus on the performance side, and define techniques for evaluating the impact of various choices in using weak memory models, such as where to put fences, and which fences to use. We make no attempt to judge certain strategies as best or most efficient, and instead provide the techniques that will allow the programmer to understand the performance implications when identifying and resolving any semantic/performance trade-offs. In particular, our technique supports the reasoned selection of macrobenchmarks to use in investigating trade-offs in using weak memory models. We demonstrate our technique on both synthetic benchmarks and real-world applications for the Linux Kernel and OpenJDK Hotspot Virtual Machine on the ARMv8 and POWERv7 architectures.

Reference object processing in on-the-fly garbage collection

Most proposals for on-the-fly garbage collection ignore the question of Javas weak and other reference types. However, we show that reference types are heavily used in DaCapo benchmarks. Of the few collectors that do address this issue, most block mutators, either globally or individually, while processing reference types. We introduce a new framework for processing reference types on-the-fly in Jikes RVM. Our framework supports both insertion and deletion write barriers. We have model checked our algorithm and incorporated it in our new implementation of the Sapphire on-the-fly collector. Using a deletion barrier, we process references while mutators are running in less than three times the time that previous approaches take while mutators are halted; our overall execution times are no worse, and often better.

Checking process-oriented operating system behaviour using CSP and refinement

Process orientation is an approach to concurrency that uses concepts of processes and message-passing communication, with whole systems constructed from layered and dynamically evolving networks of communicating processes. The work described in this paper relates to the automatic model generation and verification of systems developed in process-oriented languages. We discuss some early applications of this technique to our experimental operating system, RMoX, as a means to giving a guarantee of correct system behaviour at a range of levels.

Safe parallelism for robotic control

During the Spring 2008 semester at Olin College, we introduced the programming language occam-pi to undergraduates as part of their first course in robotics. Students were able to explore image processing and autonomous behavioral control in a parallel programming language on a small mobile robotics platform with just two weeks of tutorial instruction. Our experiences to date suggest that the language and tools we have developed allow the concise expression of complex robotic control systems, and enable the integration of events from the environment in a consistent and safe model for parallel control that is directly expressed in software.