/contrib/ntp/util/jitter.c
https://bitbucket.org/freebsd/freebsd-head/ · C · 137 lines · 88 code · 17 blank · 32 comment · 12 complexity · 9bcdb403f4e9f30c721e0d95ccb08ac9 MD5 · raw file
- /*
- * 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
- * reads the system clock and, finally, writes out the time values for
- * later analysis. From this you can determine the jitter and if the
- * clock ever runs backwards.
- */
- #ifdef HAVE_CONFIG_H
- # include <config.h>
- #endif
- #include <stdio.h>
- #include <sys/time.h>
- #include <stdlib.h>
- #include "jitter.h"
- #define NBUF 80002
- #define FRAC 4294967296. /* a bbbbillion */
- #define JAN_1970 2208988800UL /* Unix base epoch */
- #define CLOCK_GETTIME /* Solaris hires clock */
- int debug;
- char progname[10];
- double sys_residual;
- double average;
- void sys_gettime(l_fp *);
- int
- main(
- int argc,
- char *argv[]
- )
- {
- l_fp tr;
- int i, j;
- double dtemp, gtod[NBUF];
- /*
- * Force pages into memory
- */
- for (i = 0; i < NBUF; i ++)
- gtod[i] = 0;
- /*
- * Construct gtod array
- */
- for (i = 0; i < NBUF; i ++) {
- get_systime(&tr);
- LFPTOD(&tr, gtod[i]);
- }
- /*
- * Write out gtod array for later processing with Matlab
- */
- average = 0;
- for (i = 0; i < NBUF - 2; i++) {
- gtod[i] = gtod[i + 1] - gtod[i];
- printf("%13.9f\n", gtod[i]);
- average += gtod[i];
- }
- /*
- * Sort the gtod array and display deciles
- */
- for (i = 0; i < NBUF - 2; i++) {
- for (j = 0; j <= i; j++) {
- if (gtod[j] > gtod[i]) {
- dtemp = gtod[j];
- gtod[j] = gtod[i];
- gtod[i] = dtemp;
- }
- }
- }
- average = average / (NBUF - 2);
- fprintf(stderr, "Average %13.9f\n", average);
- fprintf(stderr, "First rank\n");
- for (i = 0; i < 10; i++)
- fprintf(stderr, "%2d %13.9f\n", i, gtod[i]);
- fprintf(stderr, "Last rank\n");
- for (i = NBUF - 12; i < NBUF - 2; i++)
- fprintf(stderr, "%2d %13.9f\n", i, gtod[i]);
- exit(0);
- }
- /*
- * get_systime - return system time in NTP timestamp format.
- */
- void
- get_systime(
- l_fp *now /* system time */
- )
- {
- double dtemp;
- #if defined(HAVE_CLOCK_GETTIME) || defined(HAVE_GETCLOCK)
- struct timespec ts; /* seconds and nanoseconds */
- /*
- * Convert Unix clock from seconds and nanoseconds to seconds.
- */
- # ifdef HAVE_CLOCK_GETTIME
- clock_gettime(CLOCK_REALTIME, &ts);
- # else
- getclock(TIMEOFDAY, &ts);
- # endif
- now->l_i = ts.tv_sec + JAN_1970;
- dtemp = ts.tv_nsec / 1e9;
- #else /* HAVE_CLOCK_GETTIME || HAVE_GETCLOCK */
- struct timeval tv; /* seconds and microseconds */
- /*
- * Convert Unix clock from seconds and microseconds to seconds.
- */
- gettimeofday(&tv, NULL);
- now->l_i = tv.tv_sec + JAN_1970;
- dtemp = tv.tv_usec / 1e6;
- #endif /* HAVE_CLOCK_GETTIME || HAVE_GETCLOCK */
- /*
- * Renormalize to seconds past 1900 and fraction.
- */
- dtemp += sys_residual;
- if (dtemp >= 1) {
- dtemp -= 1;
- now->l_i++;
- } else if (dtemp < -1) {
- dtemp += 1;
- now->l_i--;
- }
- dtemp *= FRAC;
- now->l_uf = (u_int32)dtemp;
- }