Worst-case Response Time Analysis Research Articles

Per Processor Spin-Based Protocols for Multiprocessor Real-Time Systems

This paper investigates preemptive spin-based global resource sharing protocols for resource-constrained real-time embedded multi-core systems based on partitioned fixed-priority preemptive scheduling. We present preemptive spin-based protocols that feature (i) an increased schedulability ratio of task sets and reduced response jitter of tasks compared to the classical non-preemptive spin-based protocol, (ii) similar memory requirements for the administration of waiting tasks as for the non-preemptive protocol whilst only causing (iii) a minimal increase of the minimal number of required stacks per core from one to at most two, and (iv) strong progress guarantees to tasks. We complement these protocols with a unified worst-case response time analysis that specializes to the classical analysis for the non-preemptive protocol. The paper includes a comparative evaluation of the preemptive protocols and the non-preemptive protocol based on synthetic data.

WCRT Analysis of CAN Messages in Gateway-Integrated In-Vehicle Networks

In modern automobiles, gateways are commonly used to connect several subsystems of controller area networks (CANs) to achieve integrated architecture and distributed cross-bus functionalities. To analyze the real-time property of such in-vehicle networks, worst-case response time (WCRT) analysis for gateway-integrated CAN messages has been studied recently. However, the WCRTs obtained are quite pessimistic. In this study, we examine in detail the various actual arriving orders of gateway messages and then propose an explorative WCRT computation method. It is proved that the obtained WCRT results are safe WCRT bounds. Experimental results for real message set demonstrate as much as 24% reduction of WCRT compared with those obtained using the state-of-the-art methods.

Response Time Analysis for Sporadic Server Based Budget Scheduling in Real Time Virtualization Environments

Virtualization techniques for embedded real-time systems typically employ TDMA scheduling to achieve temporal isolation among different virtualized applications. Recent work already introduced sporadic server based solutions relying on budgets instead of a fixed TDMA schedule. While providing better average-case response times for IRQs and tasks, a formal response time analysis for the worst-case is still missing. In order to confirm the advantage of a sporadic server based budget scheduling, this paper provides a worst-case response time analysis. To improve the sporadic server based budget scheduling even more, we provide a background scheduling implementation which will also be covered by the formal analysis. We show correctness of the analysis approach and compare it against TDMA based systems. In addition to that, we provide response time measurements from a working hypervisor implementation on an ARM based development board.

Worst-Case Response Time Analysis of a Synchronous Dataflow Graph in a Multiprocessor System with Real-Time Tasks

In this article, we propose a novel technique that estimates a tight upper bound of the worst-case response time (WCRT) of a synchronous dataflow (SDF) graph when the SDF graph shares processors with other real-time tasks. When an SDF graph is executed at runtime under a self-timed or static assignment scheduling policy on a multi-processor system, static scheduling of the SDF graph does not guarantee the satisfaction of latency constraints since changes to the schedule may result in timing anomalies. To estimate the WCRT of an SDF graph with a given mapping and scheduling result, we first construct a task instance dependency graph that depicts the dependency between node executions in a static schedule. The proposed technique combines two techniques in a novel way: schedule time bound analysis and response time analysis. The former is used to consider the interference between task instances in the same SDF graph, and the latter is used to consider the interference from other real-time tasks. Through extensive experiments with synthetic examples and benchmarks, we verify the superior performance of the proposed technique compared to other existent techniques.

Architecture and analysis of a dynamically-scheduled real-time memory controller

Memory controller design is challenging as mixed time-criticality embedded systems feature an increasing diversity of real-time (RT) and non-real-time (NRT) applications with variable transaction sizes. To satisfy the requirements of the applications, tight bounds on the worst-case response time (WCRT) of memory transactions must be provided to RT applications, while the lowest possible average response time must be given to the remaining applications. Existing real-time memory controllers cannot efficiently achieve this goal as they either bound the WCRT by sacrificing the average response time, or cannot efficiently support variable transaction sizes. In this article, we propose to use dynamic command scheduling, which is capable of efficiently dealing with transactions with variable sizes. The three main contributions of this article are: (1) a memory controller architecture consisting of a front-end and a back-end, where the former uses a TDM arbiter with a new work-conserving policy and the latter has a dynamic command scheduling algorithm that is independent of the front-end, (2) a formalization of the timings of the memory transactions for the proposed algorithm and architecture, and (3) an analysis of WCRT for transactions to capture the behavior of both the front-end and the back-end. This WCRT analysis supports variable transaction sizes and different degrees of bank parallelism. The critical part of the WCRT is the worst-case execution time (WCET) of a transaction, which is the time spent on command scheduling in the back-end. The WCET is bounded by two techniques applied to both fixed and variable transaction sizes, respectively. We experimentally evaluate the proposed memory controller and compare to an existing semi-static approach. The results demonstrate that dynamic command scheduling significantly outperforms the semi-static approach in the average case, while it performs equally well or better in the worst-case with only a few exceptions. The former reduces the average response time for NRT applications, and the latter pertains the WCRT for RT applications.

Worst Case Response Time Analysis of Sporadic Traffic in MVB

The Multifunction Vehicle Bus (MVB) protocol is well applied to train network control system where a set of process variables must be transferred between network devices. To cope with the real-time requirements of such system, the MVB protocol is designed to support both periodic and sporadic traffic. The periodic traffic is handled according to a static scheduling table, thus the schedulability can be certain after system initialization. However, for the sporadic traffic, the situation is different due to their irregular occurrence in the system. Therefore, more complex analysis must be made in order to guarantee its timing requirements. In this paper, a schedulability analysis is made by executing worst case response time analysis for sporadic traffic in MVB network.

A Technique to Calculate Cache Related Preemption Delay Using Constraints on Non-nested Preemptions

Abstract Caches incur an indirect cost to the response times of tasks due to preemptions in a task system. Hence the computation of Cache Related Preemption Delay (CRPD) is an important problem to assess the schedulability of a task system. In this paper, we have introduced the concept of inhibiting and non-nested preemptions. We have proposed a novel method to calculate tight upper and lower bounds on the number of preemptions of every task in the task-system across all phases . The problem of calculation of CRPD is modelled as a constraint satisfaction problem that can be solved by using Integer Linear Programming (ILP). The CRPD values are integrated in the worst case response time analysis.

Improved Blocking Time Analysis and Evaluation for the Multiprocessor Priority Ceiling Protocol

The Multiprocessor Priority Ceiling Protocol (MPCP) is a classic suspension-based real-time locking protocol for partitioned fixed-priority (P-FP) scheduling. However, existing blocking time analysis is pessimistic under the P-FP + MPCP scheduling, which negatively impacts the schedulability for real-time tasks. In this paper, we model each task as an alternating sequence of normal and critical sections, and use both the best-case execution time (BCET) and the worst-case execution time (WCET) to describe the execution requirement for each section. Based on this model, a novel analysis is proposed to bound shared resource requests. This analysis uses BCET to derive the lower bound on the inter-arrival time for shared resource requests, and uses WCET to obtain the upper bound on the execution time of a task on critical sections during an arbitrary time interval of Δt. Based on this analysis, improved blocking analysis and its associated worst-case response time (WCRT) analysis are proposed for P-FP + MPCP scheduling. Schedulability experiments indicate that the proposed method outperforms the existing methods and improves the schedulability significantly.

Integrating mixed transmission and practical limitations with the worst-case response-time analysis for Controller Area Network

The existing worst-case response-time analysis for Controller Area Network (CAN) calculates upper bounds on the response times of messages that are queued for transmission either periodically or sporadically. However, it does not support the analysis of mixed messages. These messages do not exhibit a periodic activation pattern and can be queued for transmission both periodically and sporadically. They are implemented by several higher-level protocols based on CAN that are used in the automotive industry. We extend the existing analysis to support worst-case response-time calculations for periodic and sporadic as well as mixed messages. Moreover, we integrate the effect of hardware and software limitations in the CAN controllers and device drivers such as abortable and non-abortable transmit buffers with the extended analysis. The extended analysis is applicable to any higher-level protocol for CAN that uses periodic, sporadic and mixed transmission modes.

Marcapasos transitorio a través de bolsa pericárdica

The existing worst-case response-time analysis for Controller Area Network (CAN) calculates upper bounds on the response times of messages that are queued for transmission either periodically or sporadically. However, it does not support the analysis of mixed messages. These messages do not exhibit a periodic activation pattern and can be queued for transmission both periodically and sporadically. They are implemented by several higher-level protocols based on CAN that are used in the automotive industry. We extend the existing analysis to support worst-case response-time calculations for periodic and sporadic as well as mixed messages. Moreover, we integrate the effect of hardware and software limitations in the CAN controllers and device drivers such as abortable and non-abortable transmit buffers with the extended analysis. The extended analysis is applicable to any higher-level protocol for CAN that uses periodic, sporadic and mixed transmission modes.

An Efficient Test Method for Rate Monotonic Schedulability

Rate Monotonic scheduling algorithm has been widely used in real-time systems for its optimality in fixed priority scheduling. Determining the Rate Monotonic schedulability of tasks is an important problem when designing a real-time system. There are exact schedulability test methods for Rate Monotonic scheduling, but the worst case response time analysis on which the exact tests are based is NP-hard. So the exact tests are often too complex to be executed on-line for large numbers of tasks. For practical use, polynomial time sufficient conditions for the Rate Monotonic schedulability have been studied. However, existing polynomial time tests are often too pessimistic. In this paper, we propose a new polynomial time sufficient condition based on the response time analysis, which is less pessimistic than existing ones. Simulation results show that our test significantly outperforms the existing tests and has performance close to the exact test.

Modified Worst Case Response Time Analysis of CAN Bus Consisting of Nodes with Buffers

Worst case response time analysis of CAN Bus is the de facto method for evaluating the real-time performance which is a key feature of industrial bus. Compared with WCRT which aimed at nodes without buffer, a modified algorithm was presented to calculate the response time of CAN Bus consisting of nodes with both hardware and software buffers. The modified algorithm introduced local blocking time to describe the effect of buffers on response time. Based on the analysis of the different structures between hardware and software buffers, modified WCRT calculation methods of messages in hardware or software buffers were presented. Then the WCRT analysis of the whole system was obtained by consolidating the response time of node and bus. Results show that the response time calculated by the modified method is much longer than that calculated by the traditional WCRT. The modified method makes the WCRT analysis more coincident with the application of engineering, which helps the design and optimization of CAN based industrial bus.

Response Time Analysis of Messages in Controller Area Network: A Review

This paper reviews the research work done on the response time analysis of messages in controller area network (CAN) from the time CAN specification was submitted for standardization (1990) and became a standard (1993) up to the present (2012). Such research includes the worst-case response time analysis which is deterministic and probabilistic response time analysis which is stochastic. A detailed view on both types of analyses is presented here. In addition to these analyses, there has been research on statistical analysis of controller area network message response times.

Optimization of task allocation and priority assignment in hard real-time distributed systems

The complexity and physical distribution of modern active safety, chassis, and powertrain automotive applications requires the use of distributed architectures. Complex functions designed as networks of function blocks exchanging signal information are deployed onto the physical HW and implemented in a SW architecture consisting of a set of tasks and messages. The typical configuration features priority-based scheduling of tasks and messages and imposes end-to-end deadlines. In this work, we present and compare formulations and procedures for the optimization of the task allocation, the signal to message mapping, and the assignment of priorities to tasks and messages in order to meet end-to-end deadline constraints and minimize latencies. Our formulations leverage worst-case response time analysis within a mixed integer linear optimization framework and are compared for performance against a simulated annealing implementation. The methods are applied for evaluation to an automotive case study of complexity comparable to industrial design problems.

The Worst-Case Response Time Analysis for FIFO-based Offset Assigned CAN Messages

The Controller Area Network (CAN) is widely employed in automotive control system networks. In the last few years, the amount of data has been increasing rapidly in these networks. With the purpose of improving CAN bandwidth efficiency, scheduling and analysis are considered to be particularly important. As an effective method, it has been known that assigning offsets to the CAN messages can reduce their worst case response time (WCRT). Meanwhile, the fact is that many commercial CAN controllers have been equipped with a priority or first-in-first-out (FIFO) queue to transmit messages to the CAN bus. However, previous researches for WCRT analysis of CAN messages either assumed a priority queue or did not consider the offset. For this reason, in this paper we propose a WCRT analysis method for CAN messages with assigned offset in the FIFO queue. We first present a critical instant theorem, then we propose two algorithms for WCRT calculation based on the given theorem. Experimental results on generated message sets and a real message set have validated the effectiveness of the proposed algorithms.

An efficient response-time analysis for real-time transactions with fixed priority assignment

In the general context of tasks with offsets (general transactions), only exponential methods are known to calculate the exact worst-case response time (WCRT) of a task. The known pseudo-polynomial techniques give an upper bound of the WCRT. In this paper, we present a new worst-case response-time analysis technique (mixed method) for transactions scheduled by fixed priorities, and executing on a uniprocessor system. This new analysis technique gives a better (i.e. lower) pseudo-polynomial upper bound of the WCRT. The main idea is to combine the principle of exact calculation and the principle of approximation calculation, in order to decrease the pessimism of WCRT analysis, thus allowing improving the upper bound of the response time provided while preserving a pseudo-polynomial complexity. Then we define the Accumulative Monotonic property on which a necessary condition of feasibility is discussed. We also propose, to speed up the exact and mixed analysis, the dominated candidate task concept that allows reducing significantly the number of critical instants to study in an analysis.

Worst-case response time analysis of real-time tasks under fixed-priority scheduling with deferred preemption

Fixed-priority scheduling with deferred preemption (FPDS) has been proposed in the literature as a viable alternative to fixed-priority pre-emptive scheduling (FPPS), that obviates the need for non-trivial resource access protocols and reduces the cost of arbitrary preemptions. This paper shows that existing worst-case response time analysis of hard real-time tasks under FPDS, arbitrary phasing and relative deadlines at most equal to periods is pessimistic and/or optimistic. The same problem also arises for fixed-priority non-pre-emptive scheduling (FPNS), being a special case of FPDS. This paper provides a revised analysis, resolving the problems with the existing approaches. The analysis is based on known concepts of critical instant and busy period for FPPS. To accommodate for our scheduling model for FPDS, we need to slightly modify existing definitions of these concepts. The analysis assumes a continuous scheduling model, which is based on a partitioning of the timeline in a set of non-empty, right semi-open intervals. It is shown that the critical instant, longest busy period, and worst-case response time for a task are suprema rather than maxima for all tasks, except for the lowest priority task. Hence, that instant, period, and response time cannot be assumed for any task, except for the lowest priority task. Moreover, it is shown that the analysis is not uniform for all tasks, i.e. the analysis for the lowest priority task differs from the analysis of the other tasks. These anomalies for the lowest priority task are an immediate consequence of the fact that only the lowest priority task cannot be blocked. To build on earlier work, the worst-case response time analysis for FPDS is expressed in terms of known worst-case analysis results for FPPS. The paper includes pessimistic variants of the analysis, which are uniform for all tasks, illustrates the revised analysis for an advanced model for FPDS, where tasks are structured as flow graphs of subjobs rather than sequences, and shows that our analysis is sustainable.

Timing analysis for preemptive multitasking real-time systems with caches

In this paper, we propose an approach to estimate the worst-case response time (WCRT) of each task in a preemptive multitasking single-processor real-time system utilizing an L1 cache. The approach combines intertask cache-eviction analysis and intratask cache-access analysis to estimate the number of cache lines that can possibly be evicted by the preempting task and also be accessed again by the preempted task after preemptions (thus requiring the preempted task to reload the cache line(s)). This cache-reload delay caused by preempting task(s) is then incorporated into WCRT analysis. Three sets of applications with up to six concurrent tasks running are used to test our approach. The experimental results show that our approach can tighten the WCRT estimate by up to 32% (1.4X) over prior state-of-the-art.

REAL TIME COMPUTING IN A HIGH PERFORMANCE CLUSTER.

Nowadays, cluster computing is a common strategy to achieve high performance computing and resolve computationally intensive tasks such as flight simulation, medical imaging, etc. Two powerful tools have been used to facilitate the development of cluster oriented applications, namely the message passing interface (MPI) and the parallel virtual machine (PVM). However, there are situations in which the application execution is time constrained, e.g., complex real-time image processing, but neither MPI or PVM take time constraints in consideration. Therefore, this paper proposes a cluster integration methodology that is amenable to real-time analysis and implementation, based on Linux with improved temporal resolution and a high-speed TDMA interconnection bus built on top of SCI.The main contribution of the paper is a worst-case response time analysis, its characterization using randomly generated task sets and its verification using a system simulator. The proposed analysis can be applied to a class of distributed real-time systems in which a set of nodes, running tasks under fixed priorities, communicate over a TDMA bus, but it is overly pessimistic in the presence of a significant percentage of communicating tasks.