Multi-core architectures pose many challenges in real-time systems, which arise from contention between concurrent accesses to shared memory. Among the available memory arbitration policies, time-division multiplexing (TDM) ensures a predictable behavior by bounding access latencies and guaranteeing bandwidth to tasks independently from the other tasks. To do so, TDM guarantees exclusive access to the shared memory in a fixed time window. TDM, however, provides a low resource utilization as it is non-work-conserving . Besides, it is very inefficient for resources having highly variable latencies, such as sharing the access to a DRAM memory. The constant length of a TDM slot is, hence, highly pessimistic and causes an underutilization of the memory. To address these limitations, we present dynamic arbitration schemes that are based on TDM. However, instead of arbitrating at the level of TDM slots, our approach operates at the granularity of clock cycles by exploiting slack time accumulated from preceding requests. This allows the arbiter to reorder memory requests, exploit the actual access latencies of requests, and thus improve memory utilization. We demonstrate that our policies are analyzable as they preserve the guarantees of TDM in the worst case, while our experiments show an improved memory utilization. We furthermore present and evaluate an efficient hardware implementation for a variant of our arbitration strategy.

中文翻译：

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多临界系统的工作节约型动态时分复用

多核架构在实时系统中提出了许多挑战，这些挑战源于对共享内存的并发访问之间的争用。在可用的内存仲裁策略中，时分复用 (TDM) 通过限制访问延迟并保证独立于其他任务的任务带宽来确保可预测的行为。为此，TDM 保证在固定时间窗口内独占访问共享内存。然而，TDM 提供低资源利用率，因为它是非工作节约的。此外，对于具有高度可变延迟的资源，例如共享对 DRAM 存储器的访问，效率非常低。因此，TDM 插槽的恒定长度是非常悲观的，并且会导致内存利用率不足。为了解决这些限制，我们提出了基于 TDM 的动态仲裁方案。然而，我们的方法不是在 TDM 时隙级别进行仲裁，而是通过利用从先前请求累积的松弛时间以时钟周期的粒度运行。这允许仲裁器对内存请求重新排序，利用请求的实际访问延迟，从而提高内存利用率。我们证明我们的策略是可分析的，因为它们在最坏的情况下保留了 TDM 的保证，而我们的实验表明内存利用率有所提高。此外，我们还为我们的仲裁策略的变体提供并评估了一种有效的硬件实现。从而提高内存利用率。我们证明我们的策略是可分析的，因为它们在最坏的情况下保留了 TDM 的保证，而我们的实验表明内存利用率有所提高。此外，我们还为我们的仲裁策略的变体提供并评估了一种有效的硬件实现。从而提高内存利用率。我们证明我们的策略是可分析的，因为它们在最坏的情况下保留了 TDM 的保证，而我们的实验表明内存利用率有所提高。此外，我们还为我们的仲裁策略的变体提供并评估了一种有效的硬件实现。