Memory latency effects in decoupled architectures

Decoupled computer architectures partition the memory access and execute functions in a computer program and achieve high-performance by exploiting the fine-grain parallelism between the two. These architectures make use of an access processor to perform the data fetch ahead of demand by the execute process and hence are often less sensitive to memory access delays than conventional architectures. Past performance studies of decoupled computers used memory systems that are interleaved or pipelined, and in those studies, latency effects were partially hidden due to interleaving. A detailed simulation study of the latency effects in decoupled computers is undertaken in this paper. Decoupled architecture performance is compared to single processors with caches. The memory latency sensitivity of cache based uniprocessors and decoupled systems is studied. Simulations are performed to determine the significance of data caches in a decoupled architecture. It is observed that decoupled architectures can reduce the peak memory bandwidth requirement, but not the total bandwidth, whereas data caches can reduce the total bandwidth by capturing locality. It may be concluded that despite their capability to partially mask the effects of memory latency, decoupled architectures still need a data cache