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.
Worst-case timing analysis of applications in multi- many-core systems has long been conducted in two steps: First, a context-independent analysis is applied to bound the WCET of each task in isolation, i.e., in absence of interferences. An overview of tools and methods for context-independent WCET analysis is provided in @cite_63 . Following the context-independent analysis, an interference analysis is performed to bound the additional latencies that may be imposed on shared resources due to external interferences.
@cite_63
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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 experim