Frequency-aware Static Timing Analysis for Power-aware Embedded Architectures
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Date
2004-03-14
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Abstract
Power is a valuable resource in embedded systems as the lifetime of many such systems is constrained by their battery capacity. Recent advances in processor design have added support for dynamic frequency/voltage scaling (DVS) for saving power. Recent work on real-time scheduling focuses on saving power in static as well as dynamic scheduling environments by exploiting idle and slack due to early task completion for DVS of subsequent tasks. These scheduling algorithms rely on a priori knowledge of worst-case execution times (WCET) for each task. They assume that DVS has no effect on the worst-case execution cycles (WCEC) of a task and scale the WCET according to the processor frequency. However, for systems with memory hierarchies, the WCEC typically does change under DVS due to frequency modulation. Hence, current assumptions used by DVS schemes result in a highly exaggerated WCET.
The research presented contributes novel techniques for tight and flexible static timing analysis particularly well-suited for dynamic scheduling schemes. The technical contributions are as follows: (1) The problem of changing execution cycles due to scaling techniques is assessed. (2) A parametric approach towards bounding the WCET statically with respect to the frequency is proposed. Using a parametric model, the effect of changes in frequency on the WCEC can be captured and, thus, the WCET over any frequency range can be accurately modeled. (3) The design and implementation of the frequency-aware static timing analysis (FAST) tool, based on prior experience with static timing analysis, is discussed. (4) Experiments demonstrate that the FAST tool provides safe upper bounds on the WCET, which are tight. The FAST tool allows the capture of the WCET of six benchmarks using equations that overestimate the WCET by less than 1%. FAST equations can also be used to improve existing DVS scheduling schemes to ensure that the effect of frequency scaling on WCET is considered and that the WCET used is not exaggerated. (5) Three DVS scheduling schemes are leveraged by incorporating FAST into them and by showing that the power consumption further decreases.
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real-time scheduling, frequency scaling, real-time systems, dynamic voltage scaling
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Degree
MS
Discipline
Computer Engineering
