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 "ntp_fp.h"
18
19 #define NBUF 800002
20 #define JAN_1970 2208988800UL /* Unix base epoch */
21 #define CLOCK_GETTIME /* Solaris hires clock */
22
23 char progname[10];
24 double sys_residual;
25 double average;
26 void sys_gettime(l_fp *);
27
28 int
main(int argc,char * argv[])29 main(
30 int argc,
31 char *argv[]
32 )
33 {
34 l_fp tr;
35 int i, j;
36 double dtemp, gtod[NBUF];
37
38 /*
39 * Force pages into memory
40 */
41 for (i = 0; i < NBUF; i ++)
42 gtod[i] = 0;
43
44 /*
45 * Construct gtod array
46 */
47 for (i = 0; i < NBUF; i ++) {
48 get_systime(&tr);
49 LFPTOD(&tr, gtod[i]);
50 }
51
52 /*
53 * Write out gtod array for later processing with Matlab
54 */
55 average = 0;
56 for (i = 0; i < NBUF - 2; i++) {
57 gtod[i] = gtod[i + 1] - gtod[i];
58 printf("%13.9f\n", gtod[i]);
59 average += gtod[i];
60 }
61
62 /*
63 * Sort the gtod array and display deciles
64 */
65 for (i = 0; i < NBUF - 2; i++) {
66 for (j = 0; j <= i; j++) {
67 if (gtod[j] > gtod[i]) {
68 dtemp = gtod[j];
69 gtod[j] = gtod[i];
70 gtod[i] = dtemp;
71 }
72 }
73 }
74 average = average / (NBUF - 2);
75 fprintf(stderr, "Average %13.9f\n", average);
76 fprintf(stderr, "First rank\n");
77 for (i = 0; i < 10; i++)
78 fprintf(stderr, "%2d %13.9f\n", i, gtod[i]);
79 fprintf(stderr, "Last rank\n");
80 for (i = NBUF - 12; i < NBUF - 2; i++)
81 fprintf(stderr, "%2d %13.9f\n", i, gtod[i]);
82 exit(0);
83 }
84
85
86 /*
87 * get_systime - return system time in NTP timestamp format.
88 */
89 void
get_systime(l_fp * now)90 get_systime(
91 l_fp *now /* system time */
92 )
93 {
94 double dtemp;
95
96 #if defined(HAVE_CLOCK_GETTIME) || defined(HAVE_GETCLOCK)
97 struct timespec ts; /* seconds and nanoseconds */
98
99 /*
100 * Convert Unix clock from seconds and nanoseconds to seconds.
101 */
102 # ifdef HAVE_CLOCK_GETTIME
103 clock_gettime(CLOCK_REALTIME, &ts);
104 # else
105 getclock(TIMEOFDAY, &ts);
106 # endif
107 now->l_i = ts.tv_sec + JAN_1970;
108 dtemp = ts.tv_nsec / 1e9;
109
110 #else /* HAVE_CLOCK_GETTIME || HAVE_GETCLOCK */
111 struct timeval tv; /* seconds and microseconds */
112
113 /*
114 * Convert Unix clock from seconds and microseconds to seconds.
115 */
116 gettimeofday(&tv, NULL);
117 now->l_i = tv.tv_sec + JAN_1970;
118 dtemp = tv.tv_usec / 1e6;
119
120 #endif /* HAVE_CLOCK_GETTIME || HAVE_GETCLOCK */
121
122 /*
123 * Renormalize to seconds past 1900 and fraction.
124 */
125 dtemp += sys_residual;
126 if (dtemp >= 1) {
127 dtemp -= 1;
128 now->l_i++;
129 } else if (dtemp < -1) {
130 dtemp += 1;
131 now->l_i--;
132 }
133 dtemp *= FRAC;
134 now->l_uf = (u_int32)dtemp;
135 }
136