benchmarks/libcpucycles 20240318_2 DragonFly

libcpucycles is a microlibrary for counting CPU cycles. Cycle counts are not as detailed as Falk diagrams but are the most precise timers available to typical software; they are central tools used in understanding and improving software performance.

The libcpucycles API is simple: include <cpucycles.h>, call cpucycles() to receive a long long whenever desired, and link with -lcpucycles.

Internally, libcpucycles understands machine-level cycle counters for amd64 (both PMC and TSC), arm32, arm64 (both PMC and VCT), mips64, ppc32, ppc64, riscv32, riscv64, s390x, sparc64, and x86. libcpucycles also understands four OS-level mechanisms, which give varying levels of accuracy: mach_absolute_time, perf_event, CLOCK_MONOTONIC, and, as a fallback, microsecond-resolution gettimeofday.

When the program first calls cpucycles(), libcpucycles automatically benchmarks the available mechanisms and selects the mechanism that does the best job. Subsequent cpucycles() calls are thread-safe and very fast. An accompanying cpucycles-info program prints a summary of cycle-counter accuracy.