Taking a closer look at memory interference effects in commercial-off-the-shelf multicore SoCs

Abstract

Commercial-off-the-shelf (COTS) multicore systems on chip (SoC) represent a cheap and convenient solution for deploying sophisticated workloads in various application domains. The combination of several CPU cores and dedicated acceleration units tightly sharing memory and interconnect systems can provide tremendous peak performance, but also threatens timing predictability due to memory interference. Even when focusing on main CPU cores only, it has been reported that task slowdown due to memory interference can surpass 10$\times$. Such poorly predictable timing behaviors bar greater adoption of COTS multicore SoCs in the domain of timing-critical applications, and motivate the wide activity of the research community to study solutions aimed at mitigating the problem. Understanding worst-case interference patterns on such hardware platforms is fundamental for building any effective memory interference control mechanism. A common assumption in the literature is that worst-case interference is generated by (and therefore assessed through) read-intensive synthetic workloads with 100% cache miss rate. Yet certain real-life workloads exhibit worse slowdown than what is generated under said assumed worst-case, so we study the interference effects of both synthetic and real-life benchmarks on different multicore SoCs. Our experiments indicate that cache thrashing causes the worst interference experienced by real-life benchmarks – due to their different usage of caches – and that there is no universal worst-case workload for every platform.