timetrials.c

#include <stdio.h>
#include <sys/time.h>
#include <pthread.h>
#include <stdlib.h>

void log_results(const char *name, int nt, double nops, double tdiff) {
  printf(" === %s (%d threads, %0.0f total ops) ===\n", name, nt, nops);
  printf("\tTotal time:   %0.2f ms\n", tdiff*1000);
  printf("\tTime per op:  %0.1f ns\n", 1000000000.0 * (tdiff/nops));
  printf("\tOps per sec:  %0.0f ops\n", nops/tdiff);
  printf("\n");
}
struct work {
  struct timeval start, finish;
  long nops_in;
  long nops_out;
  double tdiff;
};

static inline void start_work(struct work *w) {
  gettimeofday(&w->start, NULL);
}

static inline void finish_work(struct work *w, long ops) {
  w->nops_out = ops;
  gettimeofday(&w->finish, NULL);
  w->tdiff = (double)(w->finish.tv_sec - w->start.tv_sec);
  w->tdiff += ((double)w->finish.tv_usec - (double)w->start.tv_usec)/1000000.0;
}
void runtrial(const char *name, void *(*f)(void *), int nt, int nl) {
  int i;
  void *unused;
  pthread_t tid[nt];
  struct timeval start, finish;
  struct work nop[nt];

  for(i=0;i<nt;i++) nop[i].nops_in = nl;
  for(i=0;i<nt;i++) pthread_create(&tid[i], NULL, f, &nop[i]);
  for(i=0;i<nt;i++) pthread_join(tid[i], &unused);

  double total_nops = 0.0, tot_time = 0.0;
  for(i=0;i<nt;i++) {
    total_nops += nop[i].nops_out;
    tot_time += nop[i].tdiff;
  }
  log_results(name, nt, total_nops, tot_time);
}

void *gethrtime_test(void *vw) {
  hrtime_t t;
  struct work *w = vw;
  long i;

  start_work(w);
  for(i=0;i<w->nops_in;i++) t = gethrtime();
  finish_work(w, i);

  return NULL;
}

void *gettimeofday_test(void *vw) {
  struct timeval dummy;
  struct work *w = vw;
  long i;

  start_work(w);
  for(i=0;i<w->nops_in;i++) gettimeofday(&dummy, NULL);
  finish_work(w, i);

  return NULL;
}

int main() {
  runtrial("gettimeofday", gettimeofday_test, 1, 10000000);
  runtrial("gettimeofday", gettimeofday_test, 16, 10000000);
  runtrial("gethrtime", gethrtime_test, 1, 10000000);
  runtrial("gethrtime", gethrtime_test, 16, 10000000);
  return 0;
}

; ./timetrials jesus2
=== gettimeofday (1 threads, 10000000 total ops) ===
Total time: 3033.23 ms
Time per op: 303.3 ns
Ops per sec: 3296813 ops

=== gettimeofday (16 threads, 160000000 total ops) ===
Total time: 52368.43 ms
Time per op: 327.3 ns
Ops per sec: 3055276 ops

=== gethrtime (1 threads, 10000000 total ops) ===
Total time: 2954.45 ms
Time per op: 295.4 ns
Ops per sec: 3384724 ops

=== gethrtime (16 threads, 160000000 total ops) ===
Total time: 50867.22 ms
Time per op: 317.9 ns
Ops per sec: 3145444 ops

; dis -F gettimeofday /usr/lib/libc.so jesus2
disassembly for /usr/lib/libc.so

_gettimeofday()
_gettimeofday: b8 05 00 00 00 movl $0x5,%eax
_gettimeofday+0x5: cd d2 int $0xd2
_gettimeofday+0x7: 8b 4c 24 04 movl 0x4(%esp),%ecx
_gettimeofday+0xb: e3 0f jcxz +0xf <_gettimeofday+0x1c>
_gettimeofday+0xd: 89 01 movl %eax,(%ecx)
_gettimeofday+0xf: b8 d3 4d 62 10 movl $0x10624dd3,%eax
_gettimeofday+0x14: f7 ea imull %edx
_gettimeofday+0x16: c1 fa 06 sarl $0x6,%edx
_gettimeofday+0x19: 89 51 04 movl %edx,0x4(%ecx)
_gettimeofday+0x1c: 31 c0 xorl %eax,%eax
_gettimeofday+0x1e: c3 ret

; dis -F gethrtime /usr/lib/libc.so ⏎ jesus2
disassembly for /usr/lib/libc.so

gethrtime()
gethrtime: b8 03 00 00 00 movl $0x3,%eax
gethrtime+0x5: cd d2 int $0xd2
gethrtime+0x7: c3 ret