Quantifying the Performance Impact of Memory Latency and Bandwidth for Big Data Workloads

In recent years, DRAM technology improvements have scaled at a much slower pace than processors. While server processor core counts grow from 33% to 50% on a yearly cadence, DDR 3/4 memory channel bandwidth has grown at a slower rate, and memory latency has remained relatively flat for some time. Combined with new computing paradigms such as big data analytics, which involves analyzing massive volumes of data in real time, there is a trend of increasing pressure on the memory subsystem. This makes it important for computer architects to understand the sensitivity of the performance of big data workloads to memory bandwidth and latency, and how these workloads compare to more conventional workloads. To address this, we present straightforward analytic equations to quantify the impact of memory bandwidth and latency on workload performance, leveraging measured data from performance counters on real systems. We demonstrate how the values of the components of these equations can be used to classify different workloads according to their inherent bandwidth requirement and latency sensitivity. Using this performance model, we show the relative sensitivities of big data, high-performance computing, and enterprise workload classes to changes in memory bandwidth and latency.