Eric S. Raymond pushed to branch master at NTPsec / ntpsec
Commits:
b14ba537 by Eric S. Raymond at 2016-09-28T07:52:06-04:00
Adapt precision/resolution measurement in ntpfrob to clock_gettime().
As a bonus, use CLOCK_MONOTONIC so the measurement is not perturbed by
NTP adjustments.
- - - - -
1 changed file:
- ntpfrob/precision.c
Changes:
=====================================
ntpfrob/precision.c
=====================================
--- a/ntpfrob/precision.c
+++ b/ntpfrob/precision.c
@@ -52,41 +52,41 @@ void precision(const iomode mode)
* MINLOOPS > 1 ensures that even if there is a STEP between the initial call
* and the first loop, it doesn't stop too early.
* Making it even greater allows MINSTEP to be reduced, assuming that the
- * chance of MINSTEP-1 other processes getting in and calling gettimeofday
+ * chance of MINSTEP-1 other processes getting in and calling clock_gettime()
* between this processes's calls.
* Reducing MINSTEP may be necessary as this sets an upper bound for the time
- * to actually call gettimeofday.
+ * to actually call clock_gettime().
*/
-#define DUSECS 1000000
+#define DNSECS 1000000000L
#define HUSECS (1024 * 1024)
-#define MINSTEP 5 /* some systems increment uS on each call */
+#define MINSTEP 5000 /* some systems increment uS on each call */
/* Don't use "1" as some *other* process may read too*/
/*We assume no system actually *ANSWERS* in this time*/
-#define MAXSTEP 20000 /* maximum clock increment (us) */
+#define MAXSTEP 20000000 /* maximum clock increment (ns) */
#define MINLOOPS 5 /* minimum number of step samples */
#define MAXLOOPS HUSECS /* Assume precision < .1s ! */
int
default_get_resolution(void)
{
- struct timeval tp;
- struct timezone tzp;
+ struct timespec tp;
long last;
int i;
long diff;
long val;
int minsteps = MINLOOPS; /* need at least this many steps */
- gettimeofday(&tp, &tzp);
- last = tp.tv_usec;
+ clock_gettime(CLOCK_MONOTONIC, &tp);
+ last = tp.tv_nsec;
for (i = - --minsteps; i< MAXLOOPS; i++) {
- gettimeofday(&tp, &tzp);
- diff = tp.tv_usec - last;
- if (diff < 0) diff += DUSECS;
+ clock_gettime(CLOCK_MONOTONIC, &tp);
+ diff = tp.tv_nsec - last;
+ if (diff < 0) diff += DNSECS;
if (diff > MINSTEP) if (minsteps-- <= 0) break;
- last = tp.tv_usec;
+ last = tp.tv_nsec;
}
+ diff /= 1000; /* step down to milliseconds */
fprintf(stderr, "resolution = %ld usec after %d loop%s\n",
diff, i, (i==1) ? "" : "s");
@@ -113,8 +113,8 @@ default_get_resolution(void)
/*
* This routine calculates the differences between successive calls to
- * gettimeofday(). If a difference is less than zero, the us field
- * has rolled over to the next second, so we add a second in us. If
+ * clock_gettime(MONOTONIC). If a difference is less than zero, the ns field
+ * has rolled over to the next second, so we add a second in ns. If
* the difference is greater than zero and less than MINSTEP, the
* clock has been advanced by a small amount to avoid standing still.
* If the clock has advanced by a greater amount, then a timer interrupt
@@ -126,36 +126,36 @@ default_get_resolution(void)
int
default_get_precision(void)
{
- struct timeval tp;
- struct timezone tzp;
+ struct timespec tp;
long last;
int i;
long diff;
long val;
- long usec;
+ long nsec;
- usec = 0;
+ nsec = 0;
val = MAXSTEP;
- gettimeofday(&tp, &tzp);
- last = tp.tv_usec;
- for (i = 0; i < MINLOOPS && usec < HUSECS;) {
- gettimeofday(&tp, &tzp);
- diff = tp.tv_usec - last;
- last = tp.tv_usec;
+ clock_gettime(CLOCK_MONOTONIC, &tp);
+ last = tp.tv_nsec;
+ for (i = 0; i < MINLOOPS && nsec < HUSECS * 1024;) {
+ clock_gettime(CLOCK_MONOTONIC, &tp);
+ diff = tp.tv_nsec - last;
+ last = tp.tv_nsec;
if (diff < 0)
- diff += DUSECS;
- usec += diff;
+ diff += DNSECS;
+ nsec += diff;
if (diff > MINSTEP) {
i++;
if (diff < val)
val = diff;
}
}
+ val /= 1000; /* step down to milliseconds */
fprintf(stderr, "precision = %ld usec after %d loop%s\n",
val, i, (i == 1) ? "" : "s");
- if (usec >= HUSECS) {
- fprintf(stderr, " (Boy this machine is fast ! usec was %ld)\n",
- usec);
+ if (nsec >= HUSECS * 1024) {
+ fprintf(stderr, " (Boy this machine is fast! nsec was %ld)\n",
+ nsec);
val = MINSTEP; /* val <= MINSTEP; fast machine */
}
diff = HUSECS;
View it on GitLab: https://gitlab.com/NTPsec/ntpsec/commit/b14ba537ba719c40389801197b2e4c01aaaf2334
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