/contrib/ntp/util/jitter.c

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