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Tighter Response-Times for Tasks with Offsets

Fulltext:


Authors:

Jukka Mäki-Turja, Mikael Sjödin

Publication Type:

Conference/Workshop Paper

Venue:

Real-time and Embedded Computing Systems and Applications Conference (RTCSA)

Publisher:

Springer-Verlag

Abstract

We present an improvement to the analysis methods for calculating approximate response times for tasks with offsets. Our improvement calculates tighter (i.e. lower) response-times than does earlier approximation methods, and simulations show that the method, under certain conditions, calculates the exact worst-case response time. We reveal, and exploit, a misconception in previous methods concerning the interference a higher priority task poses on a lower priority task. In this paper we show how the generally accepted concept of ``released for execution'' interference produces unnecessary pessimistic response times for the approximate response time analysis (RTA), presented by Tindell and Palencia Gutierrez et al. This concept of interference does not cause any pessimism in response-time analysis for tasks without offsets (neither in the exact analysis with offsets), and has thus remained undetected over the years. Instead, we propose the concept of ``imposed'' interference, which more accurately captures the interference a task causes a lower priority task. We provide formal proofs that ``imposed'' interference is never higher than ``released for execution'' interference and that it never underestimates the interference caused by higher priority tasks. We also show, by simulations on randomly generated task sets, that our improvement results in response times that outperform previous approximate methods. A typical improvement results in about 12% better admission probability (more than 30% under certain circumstances can be obtained).

Bibtex

@inproceedings{Maki-Turja622,
author = {Jukka M{\"a}ki-Turja and Mikael Sj{\"o}din},
title = {Tighter Response-Times for Tasks with Offsets},
month = {August},
year = {2004},
booktitle = {Real-time and Embedded Computing Systems and Applications Conference (RTCSA)},
publisher = {Springer-Verlag},
url = {http://www.es.mdu.se/publications/622-}
}