Supporting RISC-V Performance Counters Through Linux Performance Analysis Tools

Increased attention to RISC-V open Instruction Set Architecture (ISA), a base ISA with a variety of optional extensions, has fueled its move from embedded devices to the high-performance computing arena, with the proliferation of RISC-V-based accelerators. However, the absence of powerful performance monitoring tools often results in poorly optimized applications and, consequently, limited computing performance. While the RISC-V ISA already defines a hardware performance monitor (HPM), research and development on RISC-V-based devices have been more focused on architectures and compilers rather than tools to support monitoring performance. To overcome this limitation, a comprehensive set of extensions and modifications to the Performance analysis tools for Linux (perf/perf_events) are proposed in this paper, and a PAPI library interface is presented. These new extensions comprise not only the Linux kernel but also the OpenSBI interface, and aim to achieve full support for the RISC-V performance monitoring specification. The conducted testing and evaluation were carried out on a HiFive Unmatched board and on a CVA6 core, but the proposed extensions, and the corresponding implementation, are easily portable to other systems.