text: Composable many-core systems enable the independent development and analysis of applications which will be executed on a shared platform where the mix of concurrently executed applications may change dynamically at run time. For each individual application, an off-line Design Space Exploration (DSE) is performed to compute several mapping alternatives on the platform, offering Pareto-optimal trade-offs in terms of real-time guarantees, resource usage, etc. At run time, one mapping is then chosen to launch the application on demand. In this context, to enable an independent analysis of each individual application at design time, so-called inter-application isolation schemes are applied which specify temporal or spatial isolation policies between applications. S.o.t.a. composable many-core systems are developed based on a fixed isolation scheme that is exclusively applied to every resource in every mapping of every application and use a timing analysis tailored to that isolation scheme to derive timing guarantees for each mapping. A fixed isolation scheme, however, heavily restricts the explored space of solutions and can, therefore, lead to suboptimality. Lifting this restriction necessitates a timing analysis that is applicable to mappings with an arbitrary mix of isolation schemes on different resources. To address this issue, we present an isolation-aware timing analysis that unlike existing analyses can handle multiple isolation schemes in combination within one mapping and delivers safe yet tight timing bounds by identifying and excluding interference scenarios that can never happen under the given combination of isolation schemes. Based on the timing analysis, we present a DSE which explores the choices of isolation scheme per resource within each mapping. Experimental results demonstrate the advantage of the proposed approach over approaches based on a fixed isolation scheme.
  @cite_61: Multi-core systems are increasingly interesting candidates for executing parallel real-time applications, in avionic, space or automotive industries, as they provide both computing capabilities and power efficiency. However, ensuring that timing constraints are met on such platforms is challenging, because some hardware resources are shared between cores. Assuming worst-case contentions when analyzing the schedulability of applications may result in systems mistakenly declared unschedulable, although the worst-case level of contentions can never occur in practice. In this paper, we present two contention-aware scheduling strategies that produce a time-triggered schedule of the application’s tasks. Based on knowledge of the application’s structure, our scheduling strategies precisely estimate the effective contentions, in order to minimize the overall makespan of the schedule. An Integer Linear Programming (ILP) solution of the scheduling problem is presented, as well as a heuristic solution that generates schedules very close to ones of the ILP (5 longer on average), with a much lower time complexity. Our heuristic improves by 19 the overall makespan of the resulting schedules compared to a worst-case contention baseline.
  @cite_26: 
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  @cite_41: Multicore architectures are increasingly used nowadays in embedded real-time systems. Parallel execution of tasks feigns the possibility of a massive increase in performance. However, this is usually not achieved because of contention on shared resources. Concurrently executing tasks mutually block their accesses to the shared resource, causing non-deterministic delays. Timing analysis of tasks in such systems is then far from trivial. Recently, several analytic methods have been proposed for this purpose, however, they cannot model complex arbitration schemes such as FlexRay which is a common bus arbitration protocol in the automotive industry. This paper considers real-time tasks composed of superblocks, i.e., sequences of computation and resource accessing phases. Resource accesses such as accesses to memories and caches are synchronous, i.e., they cause execution on the processing core to stall until the access is served. For such systems, the paper presents a state-based modeling and analysis approach based on Timed Automata which can model accurately arbitration schemes of any complexity. Based on it, we compute safe bounds on the worst-case response times of tasks. The scalability of the approach is increased significantly by abstracting several cores and their tasks with one arrival curve, which represents their resource accesses and computation times. This curve is then incorporated into the Timed Automata model of the system. The accuracy and scalability of the approach are evaluated with a real-world application from the automotive industry and benchmark applications.
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  @cite_43: The last decade has witnessed a major shift towards the deployment of embedded applications on multi-core platforms. However, real-time applications have not been able to fully benefit from this transition, as the computational gains offered by multi-cores are often offset by performance degradation due to shared resources, such as main memory. To efficiently use multi-core platforms for real-time systems, it is hence essential to tightly bound the interference when accessing shared resources. Although there has been much recent work in this area, a remaining key problem is to address the diversity of memory arbiters in the analysis to make it applicable to a wide range of systems. This work handles diverse arbiters by proposing a general framework to compute the maximum interference caused by the shared memory bus and its impact on the execution time of the tasks running on the cores, considering different bus arbiters. Our novel approach clearly demarcates the arbiter-dependent and independent stages in the analysis of these upper bounds. The arbiter-dependent phase takes the arbiter and the task memory-traffic pattern as inputs and produces a model of the availability of the bus to a given task. Then, based on the availability of the bus, the arbiter-independent phase determines the worst-case request-release scenario that maximizes the interference experienced by the tasks due to the contention for the bus. We show that the framework addresses the diversity problem by applying it to a memory bus shared by a fixed-priority arbiter, a time-division multiplexing (TDM) arbiter, and an unspecified work-conserving arbiter using applications from the MediaBench test suite. We also experimentally evaluate the quality of the analysis by comparison with a state-of-the-art TDM analysis approach and consistently showing a considerable reduction in maximum interference.
  @cite_40: Hard real-time embedded systems impose a strict latency requirement on interconnection subsystems. In the case of network-on-chip (NoC), this means each packet of a traffic stream has to be delivered within a time interval. In addition, with the increasing complexity of NoC, it consumes a significant portion of total chip power, which boosts the power footprint of such chips. In this work, we propose a methodology to minimize the energy consumption of NoC without violating the pre-specified latency deadlines of real-time applications. First, we develop a formal approach based on network calculus to obtain the worst-case delay bound of all packets, from which we derive a safe estimate of the number of cycles that a packet can be further delayed in the network without violating its deadline---the worst-case slack. With this information, we then develop an optimization algorithm that trades the slacks for lower NoC energy. Our algorithm recognizes the distribution of slacks for different traffic streams, and assigns different voltages and frequencies to different routers to achieve NoC energy-efficiency, while meeting the deadlines for all packets.
  @cite_15: In this paper we introduce a response time analysis technique for Synchronous Data Flow programs mapped to multiple parallel dependent tasks running on a compute cluster of the Kalray MPPA-256 many-core processor. The analysis we derive computes a set of response times and release dates that respect the constraints in the task dependency graph. We extend the Multicore Response Time Analysis (MRTA) framework by deriving a mathematical model of the multi-level bus arbitration policy used by the MPPA. Further, we refine the analysis to account for the release dates and response times of co-runners, and the use of memory banks. Further improvements to the precision of the analysis were achieved by splitting each task into two sequential phases, with the majority of the memory accesses in the first phase, and a small number of writes in the second phase. Our experimental evaluation focused on an avionics case study. Using measurements from the Kalray MPPA-256 as a basis, we show that the new analysis leads to response times that are a factor of 4.15 smaller for this application, than the default approach of assuming worst-case interference on each memory access.
  @cite_34: In this paper, we introduce a Multicore Response Time Analysis (MRTA) framework. This framework is extensible to different multicore architectures, with various types and arrangements of local memory, and different arbitration policies for the common interconnects. We instantiate the framework for single level local data and instruction memories (cache or scratchpads), for a variety of memory bus arbitration policies, including: Round-Robin, FIFO, Fixed-Priority, Processor-Priority, and TDMA, and account for DRAM refreshes. The MRTA framework provides a general approach to timing verification for multicore systems that is parametric in the hardware configuration and so can be used at the architectural design stage to compare the guaranteed levels of performance that can be obtained with different hardware configurations. The MRTA framework decouples response time analysis from a reliance on context independent WCET values. Instead, the analysis formulates response times directly from the demands on different hardware resources.
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  @cite_11: In this paper, we discuss a real-time on-chip communication service with a priority-based wormhole switching policy. A novel off-line schedulability analysis approach is presented. By evaluating diverse inter-relationships among the traffic-flows, this approach can predict the packet network latency based on two quantifiable different delays: direct interference from higher priority traffic-flows and indirect interference from other higher priority traffic-flows. Due to the inevitable existence of parallel interference, we prove that the general problem of determining the exact schedulability of real-time traffic-flow over the on- chip network is NP-hard. However the results presented do form an upper bound. In addition, an error in a previous published scheduling approach is illustrated and remedied. Utilizing this analysis scheme, we can flexibly evaluate at design time the schedulability of a set of traffic-flows with different QoS requirements on a real-time SoC NoC communication platform.
summary: Multi- many-core timing analyses predominantly focus on worst-case interference analysis based on the context-independent characteristics of each task and message. For instance, the analyses presented in @cite_34 @cite_19 @cite_26 @cite_60 @cite_36 @cite_42 @cite_20 @cite_8 bound the WCRT of tasks in a multi-core setup where several cores are connected to one or more memories over shared buses. @cite_34 @cite_26 , a framework for multi-core response time analysis is presented for a preemptive FP core scheduling policy coupled with multiple memory bus arbitration policies, e.g., TDM , RR , and FP . Targeting mixed-criticality systems, @cite_41 @cite_36 analyze WCRT under a non-preemptive FP core scheduling policy and a RR memory bus arbitration. The authors of @cite_15 @cite_8 present response time analyses for non-preemptive FP core scheduling policy and a multi-level bus arbitration scheme which combines RR and FP policies. @cite_61 , memory bus interference is bounded using an ILP-based timing analysis under a RR bus arbitration policy. The framework presented in @cite_43 , analyzes memory bus interference under a variety of arbitration policies, e.g., TDM and FP . Concerning the NOC , in @cite_11 and @cite_40 NOC transfer delays are analyzed under FP and RR link arbitration policies, respectively.