#include <stdio.h>
#include <unistd.h>
#include <sys/mman.h> /* for mmap and MCL_CURRENT */
#include <stdlib.h> /* for atoi */
#include <asm/msr.h> /* for rdtsc */

#define __USE_GNU 
#include <sched.h> /* for sched_xxxx */

#define NB_TEST 60000000000ULL

#include <string.h>

float get_cpu_clock_speed()
{
  FILE *fp;
  char buffer[1024];
  size_t bytes_read;
  char *match;
  float clock_speed;

  fp = fopen ("/proc/cpuinfo", "r");
  bytes_read = fread (buffer, 1, sizeof (buffer), fp);
  fclose (fp);
  if (bytes_read == 0 || bytes_read == sizeof (buffer))
    return 0;

  buffer[bytes_read] = '\0';

  match = strstr (buffer, "cpu MHz");

  if (match == NULL)
    return 0;

  sscanf (match, "cpu MHz : %f", &clock_speed);
 
  return clock_speed;
}


int main(int argc,char **argv)
{
 unsigned long long max,dt;
 float frequency;
 int cptr;
 long long i;
 struct sched_param sched_param;
 double duree;
 union {
   unsigned long long total;
   struct {
     unsigned long MSL;
     unsigned long LSL;
   };
 } tempsdeb,tempsfin,t1,t2,tmax1,tmax2;
 cpu_set_t new_mask;
 pid_t p = 0;
 int ret;

  if (argc!=2)
  {
     fprintf(stderr,"error usage:%s <NUM_CPU>\n",argv[0]);
     return -1;
  }
 
  CPU_ZERO(&new_mask);
  CPU_SET(atoi(argv[1]),&new_mask);
  ret = sched_setaffinity(p,sizeof(cpu_set_t) , &new_mask);
  rdtsc(tempsdeb.MSL,tempsdeb.LSL);
  printf(" time begin %Lx \n",tempsdeb.total);
  sched_param.sched_priority =99;
  cptr = sched_setscheduler(getpid(), SCHED_FIFO,&sched_param );
  cptr = mlockall(MCL_CURRENT);
  printf("cptr mlockall %d\n",cptr);

 
 max=0;
 rdtsc(t1.MSL,t1.LSL);
 for (i = 0; i < NB_TEST; i++)
   {
	 rdtsc(t2.MSL,t2.LSL);
	 dt = t2.total - t1.total;
	 if ( dt > max) 
	 { max = dt;
	  tmax1.total = t1.total;
	  tmax2.total = t2.total;
	  }
	 t1.total = t2.total;
   }

 rdtsc(tempsfin.MSL,tempsfin.LSL);

 printf(" time end %Lx \n",tempsfin.total);
 printf(" time max 1  %Lx \n",tmax1.total);
 printf(" time max 2  %Lx \n",tmax2.total);

 frequency = get_cpu_clock_speed();

  if (frequency == 0)
	  return -1;

 duree =((double) (tempsfin.total - tempsdeb.total))/(frequency*1000000);

 printf("Test duration %f s max detected %.0f µs\n",duree,((double)max)/(frequency));

 return 0;
}