/* $NetBSD: hist.c,v 1.1.1.1 2000/03/29 12:38:59 simonb Exp $ */ /* * This program can be used to calibrate the clock reading jitter of a * particular CPU and operating system. It first tickles every element * of an array, in order to force pages into memory, then repeatedly calls * gettimeofday() and, finally, writes out the time values for later * analysis. From this you can determine the jitter and if the clock ever * runs backwards. */ #ifdef HAVE_CONFIG_H #include #endif #include #include #include #include "ntp_types.h" #define NBUF 100001 /* size of basic histogram */ #define NSRT 20000 /* size of overflow histogram */ #define NCNT (600 * 1000000) /* sample interval (us) */ int col P((long *, long *)); int main( int argc, char *argv[] ) { struct timeval ts, tr, tp; struct timezone tzp; int i, j, n; long t, u, v, w, gtod[NBUF], ovfl[NSRT]; /* * Force pages into memory */ for (i = 0; i < NBUF; i++) gtod[i] = 0; for (i = 0; i < NSRT; i++) ovfl[i] = 0; /* * Construct histogram */ n = 0; gettimeofday(&ts, &tzp); t = ts.tv_sec * 1000000 + ts.tv_usec; v = t; while (1) { gettimeofday(&tr, &tzp); u = tr.tv_sec * 1000000 + tr.tv_usec; if (u - v > NCNT) break; w = u - t; if (w <= 0) { /* printf("error <= 0 %ld %d %d, %d %d\n", w, ts.tv_sec, ts.tv_usec, tr.tv_sec, tr.tv_usec); */ } else if (w > NBUF - 1) { ovfl[n] = w; if (n < NSRT - 1) n++; } else { gtod[w]++; } ts = tr; t = u; } /* * Write out histogram */ for (i = 0; i < NBUF - 1; i++) { if (gtod[i] > 0) printf("%ld %ld\n", i, gtod[i]); } if (n == 0) return; qsort((char *)ovfl, (int)n, sizeof(long), col); w = 0; j = 0; for (i = 0; i < n; i++) { if (ovfl[i] != w) { if (j > 0) printf("%ld %ld\n", w, j); w = ovfl[i]; j = 1; } else j++; } if (j > 0) printf("%ld %ld\n", w, j); exit(0); } int col( long *x, long *y ) { return (*x - *y); }