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Abstract-The potential for destructive interference between running processes is increased as Chip Multiprocessors (CMPs) share more on-chip resources. We believe that understanding the nature of memory system interference is vital to achieve good fairness/complexity/performance trade-offs in CMPs. Our goal in this work is to quantify the latency penalties due to interference in all hardware-controlled, shared units (i.e. the onchip interconnect, shared cache and memory bus). To achieve this, we simulate a wide variety of realistic CMP architectures. In particular, we vary the number of cores, interconnect topology, shared cache size and off-chip memory bandwidth. We observe that interference in the off-chip memory bus accounts for between 63% and 87% of the total interference impact while the impact of cache capacity interference can be lower than indicated by previous studies (between 5% and 32% of the total impact). In addition, as much as 11% of the total impact can be due to uncontrolled allocation of shared cache Miss Status Holding Registers (MSHRs).

The pressure on off-chip memory increases significantly as more cores compete for the same resources. A CMP deals with the memory wall by exploiting thread level parallelism (TLP), shifting the focus from reducing overall memory latency to memory throughput. This extends to the memory controller where the 3D structure of modern DRAM is exploited to increase throughput.Traditionally, prefetching reduces latency by fetching data before it is needed. In this paper we explore how prefetching can be used to increase memory throughput. We present our own low-cost open-page prefetch scheduler that exploits the 3D structure of DRAM when issuing prefetches. We show that because of the complex structure of modern DRAM, prefetches can be made cheaper than ordinary reads, thus making prefetching beneficial even when prefetcher accuracy is low. As a result, prefetching with good coverage is more important than high accuracy. By exploiting this observation our low-cost open page scheme increases performance and QoS. Furthermore, we explore how prefetches should be scheduled in a state of the art memory controller by examining sequential, scheduled region, CZone/Delta Correlation and reference prediction table prefetchers.

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