/* * 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. */#include <sys/time.h>#include <stdio.h>#include <sys/timex.h>#define NBUF 20002#define ntp_gettime(t)  syscall(SYS_ntp_gettime, (t))#define ntp_adjtime(t)  syscall(SYS_ntp_adjtime, (t))intmain(	int argc,	char *argv[]	){	struct timeval ts, tr;	struct ntptimeval ntv;	long temp, j, i, gtod[NBUF];	temp = ntp_gettime(&ntv);	ts = ntv.time;	if (temp < 0) {		printf("NTP precision time kernel not available\n");		exit(0);	}	/*	 * Force pages into memory	 */	for (i = 0; i < NBUF; i ++)		gtod[i] = 0;	/*	 * Construct gtod array	 */	for (i = 0; i < NBUF; i ++) {		(void)ntp_gettime(&ntv);/*printf("%08lx %08lx\n", ntv.time.tv_sec, ntv.time.tv_usec);*/		tr = ntv.time;		gtod[i] = (tr.tv_sec - ts.tv_sec) * 1000000000 + tr.tv_usec;	}	/*	 * Write out gtod array for later processing with S	 */	for (i = 0; i < NBUF - 2; i++) {/*		  printf("%lu\n", gtod[i]);*/				gtod[i] = gtod[i + 1] - gtod[i];		printf("%lu\n", gtod[i]);	}	/*	 * Sort the gtod array and display deciles	 */	for (i = 0; i < NBUF - 2; i++) {		for (j = 0; j <= i; j++) {			if (gtod[j] > gtod[i]) {				temp = gtod[j];				gtod[j] = gtod[i];				gtod[i] = temp;			}		}	}	fprintf(stderr, "First rank\n");	for (i = 0; i < 10; i++)	    fprintf(stderr, "%10ld%10ld\n", i, gtod[i]);	fprintf(stderr, "Last rank\n");	for (i = NBUF - 12; i < NBUF - 2; i++)	    fprintf(stderr, "%10ld%10ld\n", i, gtod[i]);	exit(0);}