Walter: Wide I/O Scaling of Number of Memory Controllers Versus Frequency and Voltage

Computational application demands do push the scaling of the number of cores, which themselves further increase the demand for more bandwidth. The use of larger rank widths and/or scaling the number of memory controllers (MCs) is a straightforward way to increase memory bandwidth. Connecting wide ranks and MCs via low-capacitance Through Silicon Vias (TSVs) favors high-bandwidth 3DStacking systems (e.g. Wide I/O). Given that voltage and frequency scaling (VFS) lower power utilization but the use of lower clock frequencies reduces bandwidth, this article proposes Walter as a Wide I/O technique that trades off scaling of the number of memory controllers (MCs) versus clock frequency and voltage (VFS) to mitigate low bandwidth and improve energy-per-bit usage. Our findings show that Walter's Wide I/O architectural benefits of using a larger number of MCs coupled with wider ranks when combined to VFS are promising: compared to the baseline for a 75% frequency/voltage reduction, MC scalability improved memory bandwidth by 2.4x and energy-per-bit reduced by 20% (most benchmarks for up to 16 MCs). Walter's architectural replacement of ranks set at specification frequencies with ones set at lower frequencies allows temperature reduction thus likely allowing further rank stacking.