1 /* $NetBSD: jitter.c,v 1.6 2020/05/25 20:47:37 christos 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 "ntp_fp.h"
20
21 #define NBUF 800002
22 #define JAN_1970 2208988800UL /* Unix base epoch */
23 #define CLOCK_GETTIME /* Solaris hires clock */
24
25 char progname[10];
26 double sys_residual;
27 double average;
28 void sys_gettime(l_fp *);
29
30 int
main(int argc,char * argv[])31 main(
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 */
91 void
get_systime(l_fp * now)92 get_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 }
138