/contrib/ntp/util/hist.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 calls
  5 * gettimeofday() and, finally, writes out the time values for later
  6 * analysis. From this you can determine the jitter and if the clock ever
  7 * runs backwards.
  8 */
  9
 10#ifdef HAVE_CONFIG_H
 11# include <config.h>
 12#endif
 13
 14#include "ntp_types.h"
 15
 16#include <stdio.h>
 17#include <stdlib.h>
 18
 19#define NBUF 100001		/* size of basic histogram */
 20#define NSRT 20000		/* size of overflow histogram */
 21#define NCNT (600 * 1000000)	/* sample interval (us) */
 22
 23int col P((long *, long *));
 24
 25int
 26main(
 27	int argc,
 28	char *argv[]
 29	)
 30{
 31	struct timeval ts, tr, tp;
 32	struct timezone tzp;
 33	int i, j, n;
 34	long t, u, v, w, gtod[NBUF], ovfl[NSRT];
 35
 36	/*
 37	 * Force pages into memory
 38	 */
 39	for (i = 0; i < NBUF; i++)
 40	    gtod[i] = 0;
 41	for (i = 0; i < NSRT; i++)
 42	    ovfl[i] = 0;
 43
 44	/*
 45	 * Construct histogram
 46	 */
 47	n = 0;
 48	gettimeofday(&ts, &tzp);
 49	t = ts.tv_sec * 1000000 + ts.tv_usec;
 50	v = t;
 51	while (1) {
 52		gettimeofday(&tr, &tzp);
 53		u = tr.tv_sec * 1000000 + tr.tv_usec; 
 54		if (u - v > NCNT)
 55		    break;
 56		w = u - t;
 57		if (w <= 0) {
 58/*
 59			printf("error <= 0 %ld %d %d, %d %d\n", w, ts.tv_sec,
 60			       ts.tv_usec, tr.tv_sec, tr.tv_usec);
 61*/
 62		} else if (w > NBUF - 1) {
 63			ovfl[n] = w;
 64			if (n < NSRT - 1)
 65			    n++;
 66		} else {
 67			gtod[w]++;
 68		}
 69		ts = tr;
 70		t = u;
 71	}
 72
 73	/*
 74	 * Write out histogram
 75	 */
 76	for (i = 0; i < NBUF - 1; i++) {
 77		if (gtod[i] > 0)
 78		    printf("%ld %ld\n", i, gtod[i]);
 79	}
 80	if (n == 0)
 81	    return;
 82	qsort(
 83#ifdef QSORT_USES_VOID_P
 84	    (void *)
 85#else
 86	    (char *)
 87#endif
 88	    ovfl, (size_t)n, sizeof(long), col);
 89	w = 0;
 90	j = 0;
 91	for (i = 0; i < n; i++) {
 92		if (ovfl[i] != w) {
 93			if (j > 0)
 94			    printf("%ld %ld\n", w, j);
 95			w = ovfl[i];
 96			j = 1;
 97		} else
 98		    j++;
 99	}
100	if (j > 0)
101	    printf("%ld %ld\n", w, j);
102 
103	exit(0);
104}
105
106int
107col(
108	long *x,
109	long *y
110	)
111{
112	return (*x - *y);
113}