-rw-r--r-- 1005 libcpucycles-20230105/cpucycles/default-perfevent.c raw
// version 20230105
// public domain
// djb
// adapted from supercop/cpucycles/perfevent.c

#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <sys/ioctl.h>
#include <sys/types.h>
#include <sys/syscall.h>
#include <linux/perf_event.h>
#include "cpucycles_internal.h"

static int fddev = -1;

long long ticks(void)
{
  long long result;

  if (read(fddev,&result,sizeof result) < sizeof result) return 0;
  return result;
}

long long ticks_setup(void)
{
  if (fddev == -1) {
    static struct perf_event_attr attr;

    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);
    if (fddev == -1) return cpucycles_SKIP;

    ioctl(fddev,PERF_EVENT_IOC_RESET,0);
    ioctl(fddev,PERF_EVENT_IOC_ENABLE,0);
  }

  return cpucycles_MAYBECYCLECOUNTER;
}