Dynamic Real-time Scheduling of Firm Periodic Tasks with Hard and Soft Aperiodic Tasks

Abstract

In this paper, we address the problem of the dynamic scheduling of skippable periodic task sets (i.e., period tasks allowing occasional skips of instances), together with aperiodic tasks. Scheduling of tasks is handled thanks to the merging of two existing approaches: the Skip-Over task model and the EDL (Earliest Deadline as Late as possible) aperiodic task server. The objective is to provide two on-line scheduling algorithms, namely EDL-RTO and EDL-BWP, in order to minimize the average response time of soft aperiodic requests, while ensuring that the QoS (Quality of Service) of periodic tasks will never be less than a specified bound. We also extend our results to the acceptance of sporadic tasks (i.e., aperiodic tasks with deadlines). We show that these novel scheduling algorithms have better performance compared to related algorithms regarding aperiodic response time and acceptance ratio.

Quality of Service Scheduling in the Firm Real-Time Systems

“…The determination of the latest start time for every red instance requires preliminary construction of the schedule by a variant of the EDL algorithm taking skips into account (Marchand & Silly-Chetto, 2006). We assume in the EDL schedule established at time τ that the instance following immediately a blue one -which is part of the current periodic instance set at time τ -is red.…”

Quality of Service Scheduling in Real-Time Systems

“…They propose and analyze an algorithm, based on a variant of Earliest Deadline First (EDF) scheduling, in order to exploit skips under the Total Bandwith Server (TBS). In previous works [10,12], we have considered the same approach but using the Earliest Deadline as Late as possible server (EDL). These results have led us to propose a raw version of the RLP algorithm (idle time schedule based on red tasks only) [11].…”

“…The main idea of this approach is to take advantage of the slack of red periodic task instances. Determination of the latest start time for every red request of the periodic task set requires preliminary construction of the schedule by a variant of the EDL algorithm taking skips into account [12]. In the EDL schedule established at time τ, we assume that the instance following immediately a blue instance which is part of the current periodic instance set at time τ, is red.…”

Dynamic scheduling of periodic skippable tasks in an overloaded real-time system

“…The main idea of this approach is to take advantage of the slack of red periodic task instances. Determination of the latest start time for every red instance of the periodic task set requires preliminary construction of the schedule as described previously and taking skips into account [8,10]. In the EDL schedule established at current time t, we assume that the instance following immediately a blue instance which is part of the current periodic instance set at time t, is red.…”