Schedulability Analysis for a Mode Transition in Real-Time Multi-core Systems

Abstract

Abstract-To enable real-time systems to adapt to dynamically changing environments, update functionalities and/or accommodate those tasks migrated from other failed sub-systems, there have been a number of studies on making timing guarantees while accounting for change of parameters and addition/deletion of tasks. While most of them have dealt with "transition" protocols that delay next task releases or discard the unfinished tasks released before the transition, such protocols are not suitable for many control systems in which missing/delaying control updates (by completing periodic tasks) even during a transition or mode-change may cause system instability or incur a significant incremental operational cost. In this paper, we focus on a transition protocol that does not miss/delay control updates during a system transition, and develop a new schedulability analysis for the transition in a real-time multi-core system, which provides sufficient timing guarantees without requiring any online information, such as the release and execution patterns of tasks and the start time of a transition. To achieve this, we extend an existing popular schedulability analysis framework for nontransitional tasks, and identify the scenarios that maximize the duration of a task's interference to another task in the case of a transition. Since the analysis works for any arbitrary transition order of tasks, we can improve the schedulability performance by enforcing a specific order. We formulate the problem of assigning an optimal transition order, and develop a solution by deriving some properties of optimality. Our evaluation results demonstrate that the proposed solution finds more schedulable task sets, which are not covered by naive approaches.

Response-Time Analysis for Multi-Mode Tasks in Real-Time Multiprocessor Systems

“…As a baseline schedulability analysis, we take the DA framework for multi-mode tasks proposed in our preliminary conference paper [17]. For all generated task sets with the four-tuple (i.e., 1000 • 4 • 9 • 8 • 9 task sets), we compare the number of schedulable task sets with µ − 1 different transitions M g ⇒ M h (1 ≤ g ≤ h = g + 1 ≤ µ) using their corresponding schedulability analyses 2 :…”

“…2, and then the relative order of tasks in each group is determined randomly (denoted by DA * seq , RTA(C) * seq , and RTA(I) * seq , respectively). Here, DA con is conducted by Theorem 1 in [17], and RTA(C) con and RTA(I) con are conducted by Theorem 1 in Subsection IV-C. Further, DA seq and DA * seq follow the analysis presented in Theorem 2 in [17], and the others are conducted by Theorem 2 in Subsection V-B. We present the simulation results for implicit-deadline tasks scheduled by FP only, as those for implicit-deadline tasks scheduled by EDF (or those for constrained-tasks scheduled by FP or EDF) exhibit a similar trend.…”

“…The other two studies aimed at incorporating single-mode tasks (i.e., independent of mode transitions) into the transition protocol [15] and reducing transition delay by exploiting a rate-based global dynamic-priority scheduling algorithm [16]. Unlike such studies, our study in the preliminary conference paper [17] supports a transition without imposing additional transition delay or task drop. Our previous study extended the existing DA framework developed for single-mode tasks on multiprocessor platforms to judge schedulability of multi-mode tasks in the presence of a given single mode transition.…”

“…Regarding global scheduling, a few studies proposed modetransition protocols that incur additional delay for a mode transition and tried to minimize the delay without any deadline miss [14]- [16]. The mode-transition protocol in our preliminary conference paper [17] is distinct from such studies in that it supports a system-wide mode transition where all tasks may switch to their new parameters without additional delay or task drop. Extending an existing popular schedulability analysis framework for single-mode tasks, called the deadline-based schedulability analysis (DA) [18], our previous study succeeded in developing a new schedulability analysis for multi-mode tasks in the presence of a mode transition.…”

Hard Real-Time Multiprocessor Scheduling Resilient to Core Failures

“…Note that the schedulability analysis with core failures can be also studied from the perspective of mode changes (e.g. [20]), whereas the functioning of the system, before and after a core failure, can be perceived as distinctive system modes. Also note that any potentially different workload requirements, before and after a failure, can be analysed with the mixed-criticality computational model (e.g.…”