1 files changed, 73 insertions, 0 deletions
diff --git a/usr.sbin/xntpd/util/jitter.c b/usr.sbin/xntpd/util/jitter.c
new file mode 100644
index 0000000..7201e87
--- /dev/null
+++ b/usr.sbin/xntpd/util/jitter.c
@@ -0,0 +1,73 @@
+/*
+ * 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]);
+}