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/*
* 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>
#define NBUF 10001
main()
{
struct timeval tp, ts, tr;
struct timezone tzp;
long temp, j, i, gtod[NBUF];
gettimeofday(&ts, &tzp);
ts.tv_usec = 0;
/*
* Force pages into memory
*/
for (i = 0; i < NBUF; i ++)
gtod[i] = 0;
/*
* Construct gtod array
*/
for (i = 0; i < NBUF; i ++) {
gettimeofday(&tp, &tzp);
tr = tp;
tr.tv_sec -= ts.tv_sec;
tr.tv_usec -= ts.tv_usec;
if (tr.tv_usec < 0) {
tr.tv_usec += 1000000;
tr.tv_sec--;
}
gtod[i] = tr.tv_sec * 1000000 + tr.tv_usec;
}
/*
* Write out gtod array for later processing with S
*/
for (i = 0; i < NBUF - 1; 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 - 1; 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 - 11; i < NBUF - 1; i++)
fprintf(stderr, "%10ld%10ld\n", i, gtod[i]);
}
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