dist/ntp/util/jitter.c

   1 /*      $NetBSD: jitter.c,v 1.2 2003/12/04 16:23:38 drochner Exp $      */
   2
   3 /*
   4  * This program can be used to calibrate the clock reading jitter of a
   5  * particular CPU and operating system. It first tickles every element
   6  * of an array, in order to force pages into memory, then repeatedly
   7  * reads the system clock and, finally, writes out the time values for
   8  * later analysis. From this you can determine the jitter and if the
   9  * clock ever runs backwards.
  10  */
  11
  12 #ifdef HAVE_CONFIG_H
  13 # include <config.h>
  14 #endif
  15
  16 #include <stdio.h>
  17 #include <sys/time.h>
  18 #include <stdlib.h>
  19 #include "jitter.h"
  20
  21 #define NBUF    80002
  22 #define FRAC    4294967296.             /* a bbbbillion */
  23 #define JAN_1970 2208988800UL           /* Unix base epoch */
  24 #define CLOCK_GETTIME                   /* Solaris hires clock */
  25
  26 int debug;
  27 char progname[10];
  28 double sys_residual;
  29 double average;
  30 void sys_gettime(l_fp *);
  31
  32 int
  33 main(
  34         int argc,
  35         char *argv[]
  36         )
  37 {
  38         l_fp tr;
  39         int i, j;
  40         double dtemp, gtod[NBUF];
  41
  42         /*
  43          * Force pages into memory
  44          */
  45         for (i = 0; i < NBUF; i ++)
  46             gtod[i] = 0;
  47
  48         /*
  49          * Construct gtod array
  50          */
  51         for (i = 0; i < NBUF; i ++) {
  52                 get_systime(&tr);
  53                 LFPTOD(&tr, gtod[i]);
  54         }
  55
  56         /*
  57          * Write out gtod array for later processing with Matlab
  58          */
  59         average = 0;
  60         for (i = 0; i < NBUF - 2; i++) {
  61                 gtod[i] = gtod[i + 1] - gtod[i];
  62                 printf("%13.9f\n", gtod[i]);
  63                 average += gtod[i];
  64         }
  65
  66         /*
  67          * Sort the gtod array and display deciles
  68          */
  69         for (i = 0; i < NBUF - 2; i++) {
  70                 for (j = 0; j <= i; j++) {
  71                         if (gtod[j] > gtod[i]) {
  72                                 dtemp = gtod[j];
  73                                 gtod[j] = gtod[i];
  74                                 gtod[i] = dtemp;
  75                         }
  76                 }
  77         }
  78         average = average / (NBUF - 2);
  79         fprintf(stderr, "Average %13.9f\n", average);
  80         fprintf(stderr, "First rank\n");
  81         for (i = 0; i < 10; i++)
  82                 fprintf(stderr, "%2d %13.9f\n", i, gtod[i]);
  83         fprintf(stderr, "Last rank\n");
  84         for (i = NBUF - 12; i < NBUF - 2; i++)
  85                 fprintf(stderr, "%2d %13.9f\n", i, gtod[i]);
  86         exit(0);
  87 }
  88
  89
  90 /*
  91  * get_systime - return system time in NTP timestamp format.
  92  */
  93 void
  94 get_systime(
  95         l_fp *now               /* system time */
  96         )
  97 {
  98         double dtemp;
  99
 100 #if defined(HAVE_CLOCK_GETTIME) || defined(HAVE_GETCLOCK)
 101         struct timespec ts;     /* seconds and nanoseconds */
 102
 103         /*
 104          * Convert Unix clock from seconds and nanoseconds to seconds.
 105          */
 106 # ifdef HAVE_CLOCK_GETTIME
 107         clock_gettime(CLOCK_REALTIME, &ts);
 108 # else
 109         getclock(TIMEOFDAY, &ts);
 110 # endif
 111         now->l_i = ts.tv_sec + JAN_1970;
 112         dtemp = ts.tv_nsec / 1e9;
 113
 114 #else /* HAVE_CLOCK_GETTIME || HAVE_GETCLOCK */
 115         struct timeval tv;      /* seconds and microseconds */
 116
 117         /*
 118          * Convert Unix clock from seconds and microseconds to seconds.
 119          */
 120         gettimeofday(&tv, NULL);
 121         now->l_i = tv.tv_sec + JAN_1970;
 122         dtemp = tv.tv_usec / 1e6;
 123
 124 #endif /* HAVE_CLOCK_GETTIME || HAVE_GETCLOCK */
 125
 126         /*
 127          * Renormalize to seconds past 1900 and fraction.
 128          */
 129         dtemp += sys_residual;
 130         if (dtemp >= 1) {
 131                 dtemp -= 1;
 132                 now->l_i++;
 133         } else if (dtemp < -1) {
 134                 dtemp += 1;
 135                 now->l_i--;
 136         }
 137         dtemp *= FRAC;
 138         now->l_uf = (u_int32)dtemp;
 139 }