Demystifying the Nvidia Ampere Architecture through Microbenchmarking and Instruction-level Analysis

Graphics processing units (GPUs) are now considered the leading hardware to accelerate general-purpose workloads such as AI, data analytics, and HPC. Over the last decade, researchers have focused on demystifying and evaluating the microarchitecture features of various GPU architectures beyond what vendors reveal. This line of work is necessary to understand the hardware better and build more efficient workloads and applications. Many works have studied the recent Nvidia architectures, such as Volta and Turing, comparing them to their successor, Ampere. However, some microarchitecture features, such as the clock cycles for the different instructions, have not been extensively studied for the Ampere architecture. In this paper, we study the clock cycles per instructions with various data types found in the instruction-set architecture (ISA) of Nvidia GPUs. Using microbenchmarks, we measure the clock cycles for PTX ISA instructions and their SASS ISA instructions counterpart. we further calculate the clock cycle needed to access each memory unit. We also demystify the new version of the tensor core unit found in the Ampere architecture by using the WMMA API and measuring its clock cycles per instruction and throughput for the different data types and input shapes. The results found in this work should guide software developers and hardware architects. Furthermore, the clock cycles per instructions are widely used by performance modeling simulators and tools to model and predict the performance of the hardware.