timesyscall.c

// Copyright (C) 2010  Benoit Sigoure
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program.  If not, see <http://www.gnu.org/licenses/>.

#include <stdio.h>
#include <stdlib.h>
#include <sys/syscall.h>
#include <time.h>
#include <unistd.h>
#include <string.h>
#include <sys/mman.h>
static inline unsigned long rdtsc(void)
{
        unsigned long low, high;

        asm volatile("rdtsc" : "=a" (low), "=d" (high));

        return ((low) | (high) << 32);
}


static inline long long unsigned time_ns(struct timespec* const ts) {
  if (clock_gettime(CLOCK_REALTIME, ts)) {
    exit(1);
  }
  return ((long long unsigned) ts->tv_sec) * 1000000000LLU
    + (long long unsigned) ts->tv_nsec;
}

int main(void) {
  const int iterations = 10000000;
  unsigned long long *results = malloc(sizeof(unsigned long long)*iterations);
  memset(results,0,sizeof(long long unsigned)*iterations);
  while(0!= mlock(results,sizeof(long long unsigned)*iterations)){}
  double total=0.0;
  unsigned long long start, stop;
  struct timespec ts;
  const long long unsigned start_ns = time_ns(&ts);
  start = rdtsc();
  for (int i = 0; i < iterations; i++) {
    if (syscall(SYS_gettid) <= 1) {
      exit(2);
    }
    stop = rdtsc();
    results[i]= stop-start;
    start = stop;
  }
  
  const long long unsigned delta = time_ns(&ts) - start_ns;
  for (int i = 0; i < iterations; i++) {
          printf("%lld\n",results[i]);
  }
//  printf("%i system calls in %lluns (%.1fns/syscall)\n",
//         iterations, delta, (delta / (float) iterations));
//  printf("%i  thread context switches in %lfns (%.1fns/ctxsw)\n",
//         iterations, total/2.1, ((total/2.1) / (float) iterations));
  return 0;
}