1 files changed, 110 insertions, 0 deletions
diff --git a/util/hist.c b/util/hist.c
new file mode 100644
index 0000000..c8cbe49
--- /dev/null
+++ b/util/hist.c
@@ -0,0 +1,110 @@
+/*
+ * 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 <config.h>
+#endif
+
+#include "ntp_types.h"
+
+#include <stdio.h>
+#include <stdlib.h>
+
+#define NBUF 100001		/* size of basic histogram */
+#define NSRT 20000		/* size of overflow histogram */
+#define NCNT (600 * 1000000)	/* sample interval (us) */
+
+int col (const void *, const void *);
+
+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(&ovfl, (size_t)n, sizeof(ovfl[0]), 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(
+	const void *vx,
+	const void *vy
+	)
+{
+	const long *x = vx;
+	const long *y = vy;
+
+	return (*x - *y);
+}