GCoM: A Detailed GPU Core Model for Accurate Analytical Modeling of Modern GPUs

Abstract

Analytical models can greatly help computer architects perform orders of magnitude faster early-stage design space exploration than using cycle-level simulators. To facilitate rapid design space exploration for graphics processing units (GPUs), prior studies have proposed GPU analytical models which capture first-order stall events causing performance degradation; however, the existing analytical models cannot accurately model modern GPUs due to their outdated and highly abstract GPU core microarchitecture assumptions. Therefore, to accurately evaluate the performance of modern GPUs, we need a new GPU analytical model which accurately captures the stall events incurred by the significant changes in the core microarchitectures of modern GPUs. We propose GCoM, an accurate GPU analytical model which faithfully captures the key core-side stall events of modern GPUs. Through detailed microarchitecture-driven GPU core modeling, GCoM accurately models modern GPUs by revealing the following key core-side stalls overlooked by the existing GPU analytical models. First, GCoM identifies the compute structural stall events caused by the limited per-sub-core functional units. Second, GCoM exposes the memory structural stalls due to the limited banks and shared nature of per-core L1 data caches. Third, GCoM correctly predicts the memory data stalls induced by the sectored L1 data caches which split a cache line into a set of sectors sharing the same tag. Fourth, GCoM captures the idle stalls incurred by the inter- and intra-core load imbalances. Our experiments using an NVIDIA RTX 2060 configuration show that GCoM greatly improves the modeling accuracy by achieving a mean absolute error of 10.0% against Accel-Sim cycle-level simulator, whereas the state-of-the-art GPU analytical model achieves a mean absolute error of 44.9%.