[Git][NTPsec/ntpsec][master] Adopt util/hist.c to use clock_gettime(2).

[Eric S. Raymond]

Eric S. Raymond pushed to branch master at NTPsec / ntpsec


Commits:
d9024785 by Eric S. Raymond at 2016-09-28T05:54:21-04:00
Adopt util/hist.c to use clock_gettime(2).

As a bonus, use the monotonic timer so the results are not affected
by any NTP slewing during the measurement.

- - - - -


2 changed files:

- util/README
- util/hist.c


Changes:

=====================================
util/README
=====================================
--- a/util/README
+++ b/util/README
@@ -11,7 +11,7 @@ hist.c::	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
+		clock_gettime() and, finally, writes out the time
 		values for later analysis. From this you can determine
 		the jitter and if the clock ever runs backwards.
 		To compile in the util directory, run waf configure and:


=====================================
util/hist.c
=====================================
--- a/util/hist.c
+++ b/util/hist.c
@@ -2,7 +2,7 @@
  * 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
+ * clock_gettime() and, finally, writes out the time values for later
  * analysis. From this you can determine the jitter and if the clock ever
  * runs backwards.
  */
@@ -13,10 +13,13 @@
 
 #include <stdio.h>
 #include <stdlib.h>
+#include <time.h>
 
-#define NBUF 100001		/* size of basic histogram */
-#define NSRT 20000		/* size of overflow histogram */
-#define NCNT (600 * 1000000)	/* sample interval (us) */
+#define NANOSECONDS	1000000000L
+
+#define NBUF 100001			/* size of basic histogram */
+#define NSRT 20000			/* size of overflow histogram */
+#define NCNT (600L * NANOSECONDS)	/* sample interval (ns) */
 
 int col (const void *, const void *);
 
@@ -26,8 +29,7 @@ main(
 	char *argv[]
 	)
 {
-	struct timeval ts, tr;
-	struct timezone tzp;
+	struct timespec ts, tr;
 	int i, j, n;
 	long t, u, v, w, gtod[NBUF], ovfl[NSRT];
 
@@ -46,20 +48,20 @@ main(
 	 * Construct histogram
 	 */
 	n = 0;
-	gettimeofday(&ts, &tzp);
-	t = ts.tv_sec * 1000000 + ts.tv_usec;
+	clock_gettime(CLOCK_MONOTONIC, &ts);
+	t = ts.tv_sec * NANOSECONDS + ts.tv_nsec;
 	v = t;
 	while (1) {
-		gettimeofday(&tr, &tzp);
-		u = tr.tv_sec * 1000000 + tr.tv_usec; 
+		clock_gettime(CLOCK_MONOTONIC, &tr);
+		u = tr.tv_sec * NANOSECONDS + tr.tv_nsec; 
 		if (u - v > NCNT)
 			break;
 		w = u - t;
 		if (w <= 0) {
 /*
 			printf("error <= 0 %ld %ld %ld, %ld %ld\n", w,
-			       (long)ts.tv_sec, (long)ts.tv_usec,
-			       (long)tr.tv_sec, (long)tr.tv_usec);
+			       (long)ts.tv_sec, (long)ts.tv_nsec,
+			       (long)tr.tv_sec, (long)tr.tv_nsec);
 */
 		} else if (w > NBUF - 1) {
 			ovfl[n] = w;



View it on GitLab: https://gitlab.com/NTPsec/ntpsec/commit/d9024785b6c5a8b648b4f6a6982b6de1d2afa286
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