1 timebench.c

/* gcc -o timebench timebench.c -lrt -O2 -fno-inline */
/* no-inline for better readable objdump -d output   */
#include <time.h>
#include <sys/time.h>
#include <sys/syscall.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define REPS 10000000

#define VARS			\
  int i;			\
  double duration;		\
  struct timespec start, end;	

#define CALC						\
  duration = end.tv_sec - start.tv_sec;			\
  duration += ((float) end.tv_nsec) / 1000000000.0;	\
  duration -= ((float) start.tv_nsec) / 1000000000.0;	\
  duration *= 1000000000 / REPS;					\

static void
bench_cgt(clockid_t clock, char *name)
{
VARS
  struct timespec ts;

  memset(&ts, 0, sizeof(ts));
  clock_gettime(CLOCK_REALTIME, &start);
  for (i = 0; i < REPS; i++) {
    clock_gettime(clock, &ts);
  }
  clock_gettime(CLOCK_REALTIME, &end);
CALC
  printf("clock_gettime(%s) execution time: %f ns\n", name, duration);
}

static void
bench_cgt_syscall(clockid_t clock, char *name)
{
VARS
  struct timespec ts;

  memset(&ts, 0, sizeof(ts));
  clock_gettime(CLOCK_REALTIME, &start);
  for (i = 0; i < REPS; i++) {
    syscall(SYS_clock_gettime, clock, &ts);
  }
  clock_gettime(CLOCK_REALTIME, &end);
CALC
  printf("clock_gettime(%s) syscall execution time: %f ns\n", name, duration);
}

static void
bench_time(void)
{
VARS

  clock_gettime(CLOCK_REALTIME, &start);
  for (i = 0; i < REPS; i++) {
    time(NULL);
  }
  clock_gettime(CLOCK_REALTIME, &end);
CALC
  printf("time() execution time: %f ns\n", duration);
}

static void
bench_gtod(void)
{
VARS
  struct timeval tv;

  clock_gettime(CLOCK_REALTIME, &start);
  for (i = 0; i < REPS; i++) {
    gettimeofday(&tv, NULL);
  }
  clock_gettime(CLOCK_REALTIME, &end);
CALC
  printf("gettimeofday() execution time: %f ns\n", duration);
}

volatile struct timespec vts;

static void
bench_v(void)
{
VARS
  struct timespec ts;

  clock_gettime(CLOCK_REALTIME, &vts);
  clock_gettime(CLOCK_REALTIME, &start);
  for (i = 0; i < REPS; i++) {
    ts = vts;
  }
  clock_gettime(CLOCK_REALTIME, &end);
CALC
  printf("volatile timespec execution time: %f ns\n", duration);
}

static void
bench_select(void)
{
VARS
  struct timeval tv;

  tv.tv_sec = 0;
  tv.tv_usec = 0;
  clock_gettime(CLOCK_REALTIME, &start);
  for (i = 0; i < REPS; i++) {
    select(0, NULL, NULL, NULL, &tv);
  }
  clock_gettime(CLOCK_REALTIME, &end);
CALC
  printf("select() execution time: %f ns\n", duration);
}

#define bench(clock) 			\
bench_cgt(clock, #clock);		\
bench_cgt_syscall(clock, #clock)

int
main(void)
{
  bench(CLOCK_REALTIME);
  bench(CLOCK_MONOTONIC);
#ifdef CLOCK_MONOTONIC_RAW
  bench(CLOCK_MONOTONIC_RAW);
#endif
#ifdef CLOCK_REALTIME_COARSE
  bench(CLOCK_REALTIME_COARSE);
#endif
#ifdef CLOCK_MONOTONIC_COARSE
  bench(CLOCK_MONOTONIC_COARSE);
#endif
  bench_time();
  bench_gtod();
  bench_v();
  bench_select();
  return(EXIT_SUCCESS);
}

2 output

clock_gettime(CLOCK_REALTIME) execution time: 21.616938 ns
clock_gettime(CLOCK_REALTIME) syscall execution time: 73.070474 ns
clock_gettime(CLOCK_MONOTONIC) execution time: 21.123462 ns
clock_gettime(CLOCK_MONOTONIC) syscall execution time: 74.661213 ns
clock_gettime(CLOCK_MONOTONIC_RAW) execution time: 76.850437 ns
clock_gettime(CLOCK_MONOTONIC_RAW) syscall execution time: 73.835467 ns
clock_gettime(CLOCK_REALTIME_COARSE) execution time: 7.176166 ns
clock_gettime(CLOCK_REALTIME_COARSE) syscall execution time: 64.750906 ns
clock_gettime(CLOCK_MONOTONIC_COARSE) execution time: 7.935776 ns
clock_gettime(CLOCK_MONOTONIC_COARSE) syscall execution time: 66.636675 ns
time() execution time: 3.947946 ns
gettimeofday() execution time: 21.515203 ns
volatile timespec execution time: 0.721741 ns
select() execution time: 221.470701 ns

3 virtualbox output

clock_gettime(CLOCK_REALTIME) execution time: 5523.867456 ns
clock_gettime(CLOCK_REALTIME) syscall execution time: 5184.366656 ns
clock_gettime(CLOCK_MONOTONIC) execution time: 5528.299328 ns
clock_gettime(CLOCK_MONOTONIC) syscall execution time: 5438.887168 ns
clock_gettime(CLOCK_MONOTONIC_RAW) execution time: 5501.085728 ns
clock_gettime(CLOCK_MONOTONIC_RAW) syscall execution time: 5281.261408 ns
clock_gettime(CLOCK_REALTIME_COARSE) execution time: 9.114048 ns
clock_gettime(CLOCK_REALTIME_COARSE) syscall execution time: 99.776320 ns
clock_gettime(CLOCK_MONOTONIC_COARSE) execution time: 9.789248 ns
clock_gettime(CLOCK_MONOTONIC_COARSE) syscall execution time: 104.612224 ns
time() execution time: 4.316992 ns
gettimeofday() execution time: 5285.404384 ns
volatile timespec execution time: 1.489872 ns
select() execution time: 367.661456 ns

4 qemu output

clock_gettime(CLOCK_REALTIME) execution time: 205.713536 ns
clock_gettime(CLOCK_REALTIME) syscall execution time: 203.797728 ns
clock_gettime(CLOCK_MONOTONIC) execution time: 216.525120 ns
clock_gettime(CLOCK_MONOTONIC) syscall execution time: 209.305139 ns
clock_gettime(CLOCK_MONOTONIC_RAW) execution time: 208.499407 ns
clock_gettime(CLOCK_MONOTONIC_RAW) syscall execution time: 203.348128 ns
clock_gettime(CLOCK_REALTIME_COARSE) execution time: 8.472448 ns
clock_gettime(CLOCK_REALTIME_COARSE) syscall execution time: 131.531040 ns
clock_gettime(CLOCK_MONOTONIC_COARSE) execution time: 8.876096 ns
clock_gettime(CLOCK_MONOTONIC_COARSE) syscall execution time: 135.566848 ns
time() execution time: 4.093056 ns
gettimeofday() execution time: 201.200128 ns
volatile timespec execution time: 0.871808 ns
select() execution time: 292.280128 ns

5 FreeBSD 9.2 (Atom D525)

clock_gettime(CLOCK_REALTIME) execution time: 133.198007 ns
clock_gettime(CLOCK_REALTIME) syscall execution time: 606.988477 ns
clock_gettime(CLOCK_MONOTONIC) execution time: 112.581098 ns
clock_gettime(CLOCK_MONOTONIC) syscall execution time: 585.660957 ns
time() execution time: 124.435171 ns
gettimeofday() execution time: 113.365549 ns
volatile timespec execution time: 5.153952 ns
select() execution time: 748.764848 ns