The current implementation of "default-perfevent" doesn't take into account perf counter multiplexing, so counters may be off if you have other perf measurement

The current implementation of "default-perfevent" doesn't take into account perf counter multiplexing, so counters may be off if you have other perf measurements running in the background. https://cpucycles.cr.yp.to/libcpucycles-20230105/cpucycles/default-perfevent.c.html https://cpucycles.cr.yp.to/libcpucycles-20230105/cpucycles/d... memset(&attr,0,sizeof attr); attr.type = PERF_TYPE_HARDWARE; attr.size = sizeof(struct perf_event_attr); attr.config = PERF_COUNT_HW_CPU_CYCLES; attr.disabled = 1; attr.exclude_kernel = 1; attr.exclude_hv = 1; fddev = syscall(__NR_perf_event_open,&attr,0,-1,-1,0); It needs to read time enabled / time running and scale returned values: attr.read_format = PERF_FORMAT_TOTAL_TIME_ENABLED | PERF_FORMAT_TOTAL_TIME_RUNNING;