+/* Windows NT Clock Routines
+ *
+ *
+ * Revision History:
+ * $Log$
+ * Revision 1.8 2000/11/19 08:03:20 dietrich
+ * From: "Colin Dancer" <colin.dancer@pyrochrome.net>
+ * To: <bugs@ntp.org>
+ * Sent: 10 November 2000 12:59
+ * Subject: NT bug in NTP 4.0.99j
+ *
+ * I've found a bug in (and produced a fix for) the NT clock interpolation
+ * code in NTP 4.0.99j.
+ *
+ * The symptoms of the problem are that gettimeofday() function on NT
+ * can be wrong by hundreds of seconds if, while a gettimeofday() call
+ * is being processed, an APC completes after the query of the performance
+ * counter but before the lock is grabbed. The most obvious fix is to move
+ * the lock to include the querying of the performance counter, but this
+ * could affect the predictability of the timestamp so I have instead
+ * tweaked the code to detect and sidestep the duff calculation.
+ *
+ * I've also found that on a loaded system the execution of the APC can be
+ * delayed, leading to errors of upto 10ms. There is no easy fix to this,
+ * but I do have code for an alternative interpolation scheme which avoids
+ * the problem on single processor systems. I'm currently integrating this
+ * along with code for deciding which algorithm to use based on whether
+ * the system is SP or MP.
+ *
+ * Created by Sven Dietrich sven@inter-yacht.com
+ *
+ */
+
+
#ifdef HAVE_CONFIG_H
#include "config.h"
#endif
/* dtemp is in micro seconds. NT uses 100 ns units,
* so a unit change in dwTimeAdjustment corresponds
- * to slewing 10 ppm on a 100 Hz system.
- * Calculate the number of 100ns units to add,
+ * to slewing 10 ppm on a 100 Hz system.
+ * Calculate the number of 100ns units to add,
* using OS tick frequency as per suggestion from Harry Pyle,
* and leave the remainder in dtemp */
dwTimeAdjustment = (DWORD)( dtemp / ppm_per_adjust_unit + (isneg ? -0.5 : 0.5)) ;
/* only adjust the clock if adjustment changes */
if (last_Adj != dwTimeAdjustment) {
- last_Adj = dwTimeAdjustment;
+ last_Adj = dwTimeAdjustment;
# ifdef DEBUG
- if (debug > 1)
+ if (debug > 1)
printf("SetSystemTimeAdjustment( %ld) + (%ld)\n", dwTimeAdjustment, units_per_tick);
# endif
dwTimeAdjustment += units_per_tick;
{
msyslog(LOG_ERR, "Can't adjust time: %m");
return 0;
- }
+ }
else {
sys_residual = dtemp / 1000000.0;
}
units_per_tick = initial_units_per_tick;
- /* Calculate the time adjustment resulting from incrementing
+ /* Calculate the time adjustment resulting from incrementing
* units per tick by 1 unit for 1 second */
ppm_per_adjust_unit = 1000000.0 / (double) every;
}
+
int
gettimeofday(
struct timeval *tv
LARGE_INTEGER LargeIntNowCount;
ULONGLONG Time;
ULONGLONG NowCount;
+ ULONGLONG PreCount; /*FIX*/
LONGLONG TicksElapsed;
LONG time_adjustment;
- /* Mark a mark ASAP. The latency to here should
+ /* Mark a mark ASAP. The latency to here should
* be reasonably deterministic
*/
+
+ PreCount = LastTimerCount; /*FIX*/
+
if (!QueryPerformanceCounter(&LargeIntNowCount)) {
msyslog(LOG_ERR, "QueryPeformanceCounter failed: %m");
exit(1);
/* Get base time we are going to extrapolate from
*/
- EnterCriticalSection(&TimerCritialSection);
+ EnterCriticalSection(&TimerCritialSection);
Count = LastTimerCount;
Time = LastTimerTime;
LeaveCriticalSection(&TimerCritialSection);
/* Calculate when now is.
- *
+ *
* Result = LastTimerTime + (NowCount - LastTimerCount) / PerfFrequency
*/
- if (NowCount >= Count)
- TicksElapsed = NowCount - Count; /* linear progression of ticks */
- else
- TicksElapsed = NowCount + (RollOverCount - Count);
+
+ if (NowCount >= Count)
+ {
+ TicksElapsed = NowCount - Count; /* linear progression of ticks */
+ }
+ else
+ {
+ /************************************************************************/
+ /* Differentiate between real rollover and the case of taking a */
+ /* perfcount then the APC coming in. */
+ /************************************************************************/
+ if (Count > PreCount) /*FIX*/
+ { /*FIX*/
+ TicksElapsed = 0; /*FIX*/
+ } /*FIX*/
+ else /*FIX*/
+ { /*FIX*/
+ TicksElapsed = NowCount + (RollOverCount - Count); /*FIX*/
+ } /*FIX*/
+ }
/* Calculate the new time (in 100's of nano-seconds)
*/
return 0;
}
-
static void CALLBACK
TimerApcFunction(
- LPVOID lpArgToCompletionRoutine,
- DWORD dwTimerLowValue,
+ LPVOID lpArgToCompletionRoutine,
+ DWORD dwTimerLowValue,
DWORD dwTimerHighValue
)
{
/* Check to see if the counter has rolled. This happens
more often on Multi-CPU systems */
- if ((ULONGLONG) LargeIntNowCount.QuadPart < LastTimerCount) {
+ if ((ULONGLONG) LargeIntNowCount.QuadPart < LastTimerCount) {
/* Counter Rolled - try and estimate the rollover point using
the nominal counter frequency divided by an estimate of the
- OS frequency */
- RollOverCount = LastTimerCount + PerfFrequency * every / HECTONANOSECONDS -
+ OS frequency */
+ RollOverCount = LastTimerCount + PerfFrequency * every / HECTONANOSECONDS -
(ULONGLONG) LargeIntNowCount.QuadPart;
#ifdef DEBUG
- msyslog(LOG_INFO,
- "Performance Counter Rollover %I64u:\rLast Timer Count %I64u\rCurrent Count %I64u",
+ msyslog(LOG_INFO,
+ "Performance Counter Rollover %I64u:\rLast Timer Count %I64u\rCurrent Count %I64u",
RollOverCount, LastTimerCount, LargeIntNowCount.QuadPart);
#endif
}
/* Now we can hang out and wait for the critical section to free up;
- we will get the CPU this timeslice. Meanwhile other tasks can use
+ we will get the CPU this timeslice. Meanwhile other tasks can use
the last value of LastTimerCount */
EnterCriticalSection(&TimerCritialSection);
LARGE_INTEGER Freq = { 0, 0 };
/* get the performance counter freq*/
- if (!QueryPerformanceFrequency(&Freq)) {
+ if (!QueryPerformanceFrequency(&Freq)) {
msyslog(LOG_ERR, "QueryPerformanceFrequency failed: %m\n");
exit (-1);
}
/* init variables with the time now */
GetSystemTimeAsFileTime(&StartTime);
- LastTimerTime = (((ULONGLONG) StartTime.dwHighDateTime) << 32) +
+ LastTimerTime = (((ULONGLONG) StartTime.dwHighDateTime) << 32) +
(ULONGLONG) StartTime.dwLowDateTime;
/* init sync objects */
DeleteCriticalSection(&TimerCritialSection);
msyslog(LOG_INFO, "The Network Time Protocol Service has stopped.");
- }
- else
+ }
+ else
msyslog(LOG_ERR, "Network Time Protocol Service Failed to Stop");
}
projects / thirdparty / ntp.git / commitdiff
