Task Scheduling Methods for Composable and Predictable MPSoC

Task Scheduling Methods for Composable and Predictable MPSoC

Nguyen, B.T.

Molnos, A.M. (mentor)
Cotofana, S.D. (mentor)

Electrical Engineering, Mathematics and Computer Science

Computer Engineering

2010-09-29

Multiprocessor Systems on a Chip (MPSoCs) are suitable platforms for executing complex embedded applications. To reduce the cost of the hardware platform, applications share resources, which may result in inter-application timing interference due to resource request conflicts. Bounding or prohibiting this interference is crucial, as the timing of real-time applications has to be predicted in each possible case. Resources that allow sharing without application interference are denoted as composable. Composability is a desired platform property, as it enables the design and analysis of applications in isolation, and their integration with linear effort. Previous work demonstrates composability for different resources, i.e., processor, interconnect, memory. Processor composability is achieved by utilizing an Operating System (OS) that schedules fixed duration task slots, using a two-level, hierarchical approach. First, the OS determines which application owns the next slot following a strict, preemptive Time Division Multiplexing (TDM) policy, and then it picks and schedules a task of that application. As scheduling decisions are taken exclusively at slots borders, when a task finishes before its slot depletes, the time left is wasted. This may result in low processor utilization for streaming applications for which the execution of a task may start after its predecessor tasks have finished. In this work we propose a new task scheduling strategy, namely application-space task scheduling that eliminates wasted slot time. We make use of the fixed duration slots and the application TDM, to preserve composability, but the application invokes the task scheduler immediately after each task finish, inside its slot. As the application-space task scheduling strategy alone may not support all types of task scheduling, e.g., preemptive, we propose to combine OS-space and application-space scheduling on the same processor. To experimentally investigate the composability and performance of our scheme we survey existing benchmarks for the embedded domain, and build a workload consisting of two streaming applications and a synthetic application. We executed these applications on an MPSoC with two processor tiles, a monitor tile, all connected by a Æthereal NoC. Our experiments indicate that mixing application-space and OS-space task schedulers is composable. Furthermore, the application-space task scheduling achieves 17% to 40% better performance than the OS-space task scheduling for the streaming applications exercised.

http://resolver.tudelft.nl/uuid:740995b0-2576-42ea-aa49-940c6e10a7ba

2010-10-05

Student theses

master thesis

(c) 2010 Nguyen, B.T.