xntpd 3.3b from UDel

[unix-history] / contrib / xntpd / util / jitter.c

/*
* This program can be used to calibrate the clock reading jitter of a
* particular CPU and operating system. It first tickles every element
* of an array, in order to force pages into memory, then repeatedly calls
* gettimeofday() and, finally, writes out the time values for later
* analysis. From this you can determine the jitter and if the clock ever
* runs backwards.
*/
#include <sys/time.h>
#include <stdio.h>

#define NBUF 10001

main()
{
       struct timeval tp, ts, tr;
       struct timezone tzp;
       long temp, j, i, gtod[NBUF];

       gettimeofday(&ts, &tzp);
       ts.tv_usec = 0;

       /*
        * Force pages into memory
        */
       for (i = 0; i < NBUF; i ++)
               gtod[i] = 0;

       /*
        * Construct gtod array
        */
       for (i = 0; i < NBUF; i ++) {
               gettimeofday(&tp, &tzp);
               tr = tp;
               tr.tv_sec -= ts.tv_sec;
               tr.tv_usec -= ts.tv_usec;
               if (tr.tv_usec < 0) {
                       tr.tv_usec += 1000000;
                       tr.tv_sec--;
               }
               gtod[i] = tr.tv_sec * 1000000 + tr.tv_usec;
       }

       /*
        * Write out gtod array for later processing with S
        */
       for (i = 0; i < NBUF - 1; i++) {
/*
               printf("%lu\n", gtod[i]);
*/
               gtod[i] = gtod[i + 1] - gtod[i];
               printf("%lu\n", gtod[i]);
       }

       /*
        * Sort the gtod array and display deciles
        */
       for (i = 0; i < NBUF - 1; i++) {
               for (j = 0; j <= i; j++) {
                       if (gtod[j] > gtod[i]) {
                               temp = gtod[j];
                               gtod[j] = gtod[i];
                               gtod[i] = temp;
                       }
               }
       }
       fprintf(stderr, "First rank\n");
       for (i = 0; i < 10; i++)
               fprintf(stderr, "%10ld%10ld\n", i, gtod[i]);
       fprintf(stderr, "Last rank\n");
       for (i = NBUF - 11; i < NBUF - 1; i++)
               fprintf(stderr, "%10ld%10ld\n", i, gtod[i]);
}