Worst-case Stall Analysis for Multicore Architectures with Two Memory Controllers

Abstract

In multicore architectures, there is potential for contention between cores when accessing shared resources, such as system memory. Such contention scenarios are challenging to accurately analyse, from a worst-case timing perspective. One way of making memory contention in multicores more amenable to timing analysis is the use of memory regulation mechanisms. It restricts the number of accesses performed by any given core over time by using periodically replenished per-core budgets. Typically, this assumes that all cores access memory via a single shared memory controller. However, ever-increasing bandwidth requirements have brought about architectures with multiple memory controllers. These control accesses to different memory regions and are potentially shared among all cores. While this presents an opportunity to satisfy bandwidth requirements, existing analysis designed for a single memory controller are no longer safe. 
This work formulates a worst-case memory stall analysis for a memory-regulated multicore with two memory controllers. This stall analysis can be integrated into the schedulability analysis of systems under fixed-priority partitioned scheduling. Five heuristics for assigning tasks and memory budgets to cores in a stall-cognisant manner are also proposed. We experimentally quantify the cost in terms of extra stall for letting all cores benefit from the memory space offered by both controllers, and also evaluate the five heuristics for different system characteristics.