Статическая проверка корректности разделения ресурсов в системах реального времени

Among issues which arise when developing software complexes for real-time systems (RTS) one should resolve common multi-task system issues of ensuring logical correctness of the system being created (preserving the integrity of informational resources, eliminating the possibility of mutual task blocking), as well as issues of ensuring dynamic correctness, specific for RTS (feasibility of the application tasks). In the long run, resolving these issues is reduced to checking the correctness of how synchronizing operators which ensure consistent execution of application tasks are scattered in the task bodies. In order to perform such checking statically, models which represent the scattering of synchronizing operators in application tasks are constructed. In this paper several methods of processing such models are proposed which are based on constructing special multi-partite graphs — graphs of synchronizing operator dependencies. Two varieties of such graphs are resented: a) graphs of bundles, which ensure verification of logical correctness of multi-task applications (correctness of intersections of critical interval pairs); and b) graphs of bundles and critical intervals, which ensure verification of dynamic correctness of RTS applications.В ряду вопросов, возникающих в ходе разработки программных комплексов для СРВ, необходимо решать как общие для многозадачных систем вопросы обеспечения логической корректности создаваемой системы (сохранение целостности информационных ресурсов, исключения возможности взаимного блокирования задач), так и специфические для СРВ вопросы динамической корректности (своевременности исполнения задач). Решение этих вопросов в конечном счете сводится к проверке корректности размещения в теле каждой из задач синхронизирующих операторов, обеспечивающих согласованное исполнение задач. Такая проверка корректности осуществляется статически. С этой целью строятся модели, отражающие размещение синхронизирующих операторов в задачах приложения. В настоящей статье предлагаются методы обработки таких моделей посредством построения специальных многодольных графов — графов зависимостей синхронизирующих операторов. Представляются две разновидности таких графов: а) графы связок, обеспечивающие проверку логической корректности многозадачных приложений, (корректность пересечений пар критических интервалов); и б) графы связок и критических интервалов, обеспечивающие проверку динамической корректности приложений для СРВ

Транзитивное наследование приоритетов в многозадачных приложениях реального времени

Control procedures for accessing shared resources in multi-task real-time software applications are analyzed. Two approaches to preventing priority inversion – basic and transitive procedures of priority inheritance – are analyzed in detail. To illustrate the considered notions and statements, concrete examples of multi-task application configurations are provided along with their execution diagrams under particular scenarios of system events, which demonstrate insufficient response time of tasks with sufficient computing resources and even mutual task clinches. The nomenclature of attributes to be included into task and resource descriptors for task management with the two priority inheritance procedures is proposed. The sufficient conditions for the basic procedure to prevent priority inheritance are formulated. The procedure of transitive priority inheritance is demonstrated to be capable of detecting a mutual task clinch in the application.Рассматриваются методы контроля доступа задач к разделяемым ресурсам в программных приложениях для систем реального времени. Приводится детальное представление двух процедур наследования приоритетов задач: непосредственной и транзитивной. Сформулированы достаточные условия, при которых применение непосредственной процедуры предотвращает инверсию приоритетов. Предложена модификация транзитивной процедуры снимающая известные ограничения на структуру приложения, накладываемые ее традиционной реализацией. Эта модификация, кроме того, обеспечивает динамическое обнаружение некорректных ситуаций типа взаимного блокирования задач с возможностью запланированной реакции на такие ситуации

A Workload Generator for Evaluating SMT Real-Time Systems

[EN] Real-time tasks have experience a significant complexity increase in the last years. We can find examples of real-time tasks in nowadays systems that control self-driving cars or multimedia systems, among others. To cope with the high performance requirements of such systems, real-time systems are moving from simple in-order processor to complex out-of-order multicore processors. Furthermore, we expect real-time systems to use simultaneous multithreading (SMT) processors in a near future since these architectures address two key design concerns of embedded systems, that is, they provide higher performance and power efficiency than single-threaded multicores. The main drawback that multicores and SMT architectures present from a real-time perspective is that they implement shared resources. Single-threaded multicores usually share the main memory and the LLC, and SMT processor share additionally most of the microarchitectural core resources. Processes running concurrently can interfere in the shared resources, which increases the performance variability and predictability of these systems. We expect an increasing effort in the next years to mitigate these drawbacks and implement real-time systems with multicore SMT processors. Workload generation is a tedious and time-consuming task in the real-time research field because the workloads dispose of many parameters that should be correctly adjusted to provide flexible and representative workloads. Typically used workload generators, however, fail when designing workloads for theses architectures because they are not aware of the architectural characteristics of SMT systems. In this paper we present the task class-based (TCB) workload generator aimed at providing workloads to evaluate real-time systems with SMT multicore processors in an ease and automatized way.Furió Novejarque, C.; Feliu-Pérez, J.; Petit Martí, SV.; Duro-Gómez, J.; Sahuquillo Borrás, J. (2018). A Workload Generator for Evaluating SMT Real-Time Systems. IEEE Computer Society. 367-374. doi:10.1109/HPCS.2018.00067S36737

Schedulability analysis of global scheduling algorithms on multiprocessor platforms

This paper addresses the schedulability problem of periodic and sporadic real-time task sets with constrained deadlines preemptively scheduled on a multiprocessor platform composed by identical processors. We assume that a global work-conserving scheduler is used and migration from one processor to another is allowed during a task lifetime. First, a general method to derive schedulability conditions for multiprocessor real-time systems will be presented. The analysis will be applied to two typical scheduling algorithms: earliest deadline first (EDF) and fixed priority (FP). Then, the derived schedulability conditions will be tightened, refining the analysis with a simple and effective technique that significantly improves the percentage of accepted task sets. The effectiveness of the proposed test is shown through an extensive set of synthetic experiments

Best Speed Fit EDF Scheduling for Performance Asymmetric Multiprocessors

In order to improve the performance of a real-time system, asymmetric multiprocessors have been proposed. The benefits of improved system performance and reduced power consumption from such architectures cannot be fully exploited unless suitable task scheduling and task allocation approaches are implemented at the operating system level. Unfortunately, most of the previous research on scheduling algorithms for performance asymmetric multiprocessors is focused on task priority assignment. They simply assign the highest priority task to the fastest processor. In this paper, we propose BSF-EDF (best speed fit for earliest deadline first) for performance asymmetric multiprocessor scheduling. This approach chooses a suitable processor rather than the fastest one, when allocating tasks. With this proposed BSF-EDF scheduling, we also derive an effective schedulability test

Schedulability analysis of global scheduling algorithms on multiprocessor platforms

This paper addresses the schedulability problem of periodic and sporadic real-time task sets with constrained deadlines preemptively scheduled on a multiprocessor platform composed by identical processors. We assume that a global work-conserving scheduler is used and migration from one processor to another is allowed during a task lifetime. First, a general method to derive schedulability conditions for multiprocessor real-time systems will be presented. The analysis will be applied to two typical scheduling algorithms: earliest deadline first (EDF) and fixed priority (FP). Then, the derived schedulability conditions will be tightened, refining the analysis with a simple and effective technique that significantly improves the percentage of accepted task sets. The effectiveness of the proposed test is shown through an extensive set of synthetic experiments

Parallelizing with BDSC, a resource-constrained scheduling algorithm for shared and distributed memory systems

International audienceWe introduce a new parallelization framework for scientific computing based on BDSC, an efficient automatic scheduling algorithm for parallel programs in the presence of resource constraints on the number of processors and their local memory size. BDSC extends Yang and Gerasoulis's Dominant Sequence Clus-tering (DSC) algorithm; it uses sophisticated cost models and addresses both shared and distributed parallel memory architectures. We describe BDSC, its integration within the PIPS compiler infrastructure and its application to the parallelization of four well-known scientific applications: Harris, ABF, equake and IS. Our experiments suggest that BDSC's focus on efficient resource man-agement leads to significant parallelization speedups on both shared and dis-tributed memory systems, improving upon DSC results, as shown by the com-parison of the sequential and parallelized versions of these four applications running on both OpenMP and MPI frameworks

Optimal virtual cluster-based multiprocessor scheduling

Scheduling of constrained deadline sporadic task systems on multiprocessor platforms is an area which has received much attention in the recent past. It is widely believed that finding an optimal scheduler is hard, and therefore most studies have focused on developing algorithms with good processor utilization bounds. These algorithms can be broadly classified into two categories: partitioned scheduling in which tasks are statically assigned to individual processors, and global scheduling in which each task is allowed to execute on any processor in the platform. In this paper we consider a third, more general, approach called cluster-based scheduling. In this approach each task is statically assigned to a processor cluster, tasks in each cluster are globally scheduled among themselves, and clusters in turn are scheduled on the multiprocessor platform. We develop techniques to support such cluster-based scheduling algorithms, and also consider properties that minimize total processor utilization of individual clusters. In the last part of this paper, we develop new virtual cluster-based scheduling algorithms. For implicit deadline sporadic task systems, we develop an optimal scheduling algorithm that is neither Pfair nor ERfair. We also show that the processor utilization bound of us-edf{m/(2m−1)} can be improved by using virtual clustering. Since neither partitioned nor global strategies dominate over the other, cluster-based scheduling is a natural direction for research towards achieving improved processor utilization bounds