138 lines
2.8 KiB
C
138 lines
2.8 KiB
C
/*
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* This program can be used to calibrate the clock reading jitter of a
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* particular CPU and operating system. It first tickles every element
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* of an array, in order to force pages into memory, then repeatedly
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* reads the system clock and, finally, writes out the time values for
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* later analysis. From this you can determine the jitter and if the
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* clock ever runs backwards.
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*/
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#ifdef HAVE_CONFIG_H
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# include <config.h>
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#endif
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#include <stdio.h>
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#include <sys/time.h>
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#include <stdlib.h>
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#include "jitter.h"
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#define NBUF 80002
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#define FRAC 4294967296. /* a bbbbillion */
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#define JAN_1970 2208988800UL /* Unix base epoch */
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#define CLOCK_GETTIME /* Solaris hires clock */
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int debug;
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char progname[10];
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double sys_residual;
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double average;
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void sys_gettime(l_fp *);
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int
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main(
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int argc,
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char *argv[]
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)
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{
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l_fp tr;
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int i, j;
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double dtemp, gtod[NBUF];
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/*
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* Force pages into memory
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*/
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for (i = 0; i < NBUF; i ++)
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gtod[i] = 0;
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/*
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* Construct gtod array
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*/
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for (i = 0; i < NBUF; i ++) {
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get_systime(&tr);
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LFPTOD(&tr, gtod[i]);
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}
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/*
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* Write out gtod array for later processing with Matlab
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*/
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average = 0;
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for (i = 0; i < NBUF - 2; i++) {
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gtod[i] = gtod[i + 1] - gtod[i];
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printf("%13.9f\n", gtod[i]);
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average += gtod[i];
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}
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/*
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* Sort the gtod array and display deciles
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*/
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for (i = 0; i < NBUF - 2; i++) {
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for (j = 0; j <= i; j++) {
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if (gtod[j] > gtod[i]) {
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dtemp = gtod[j];
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gtod[j] = gtod[i];
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gtod[i] = dtemp;
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}
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}
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}
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average = average / (NBUF - 2);
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fprintf(stderr, "Average %13.9f\n", average);
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fprintf(stderr, "First rank\n");
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for (i = 0; i < 10; i++)
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fprintf(stderr, "%2d %13.9f\n", i, gtod[i]);
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fprintf(stderr, "Last rank\n");
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for (i = NBUF - 12; i < NBUF - 2; i++)
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fprintf(stderr, "%2d %13.9f\n", i, gtod[i]);
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exit(0);
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}
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/*
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* get_systime - return system time in NTP timestamp format.
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*/
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void
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get_systime(
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l_fp *now /* system time */
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)
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{
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double dtemp;
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#if defined(HAVE_CLOCK_GETTIME) || defined(HAVE_GETCLOCK)
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struct timespec ts; /* seconds and nanoseconds */
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/*
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* Convert Unix clock from seconds and nanoseconds to seconds.
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*/
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# ifdef HAVE_CLOCK_GETTIME
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clock_gettime(CLOCK_REALTIME, &ts);
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# else
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getclock(TIMEOFDAY, &ts);
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# endif
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now->l_i = ts.tv_sec + JAN_1970;
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dtemp = ts.tv_nsec / 1e9;
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#else /* HAVE_CLOCK_GETTIME || HAVE_GETCLOCK */
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struct timeval tv; /* seconds and microseconds */
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/*
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* Convert Unix clock from seconds and microseconds to seconds.
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*/
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gettimeofday(&tv, NULL);
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now->l_i = tv.tv_sec + JAN_1970;
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dtemp = tv.tv_usec / 1e6;
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#endif /* HAVE_CLOCK_GETTIME || HAVE_GETCLOCK */
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/*
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* Renormalize to seconds past 1900 and fraction.
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*/
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dtemp += sys_residual;
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if (dtemp >= 1) {
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dtemp -= 1;
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now->l_i++;
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} else if (dtemp < -1) {
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dtemp += 1;
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now->l_i--;
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}
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dtemp *= FRAC;
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now->l_uf = (u_int32)dtemp;
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}
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