[PATCH 5/10] NTP: convert time_offset to nsec

From: Roman Zippel
Date: Wed Dec 21 2005 - 18:23:29 EST

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This converts time_offset into a scaled time_offset value. By scaling
the value it avoids completely the compensation in second_overflow().
Some calculations for the time_freq adjustments are now done using 64bit
values, which allows a better resolution and makes the NTP4 conversion
easier (the nsec resolution and increased time_constant range makes it
hard to keep it 32bit values).

Signed-off-by: Roman Zippel <zippel@xxxxxxxxxxxxxx>

---

arch/powerpc/kernel/time.c | 6 ++-
include/linux/timex.h | 6 +--
kernel/time.c | 34 +++++++++++++---------
kernel/timer.c | 68 +++++++++++++++++++--------------------------
4 files changed, 58 insertions(+), 56 deletions(-)

Index: linux-2.6-mm/arch/powerpc/kernel/time.c
===================================================================
--- linux-2.6-mm.orig/arch/powerpc/kernel/time.c 2005-12-21 12:09:49.000000000 +0100
+++ linux-2.6-mm/arch/powerpc/kernel/time.c 2005-12-21 12:12:08.000000000 +0100
@@ -794,12 +794,14 @@ void ppc_adjtimex(void)
*/
if ( time_offset < 0 ) {
ltemp = -time_offset;
- ltemp <<= SHIFT_USEC - SHIFT_UPDATE;
+ ltemp <<= SHIFT_USEC - SHIFT_HZ;
+ ltemp = ltemp * HZ / 1000;
ltemp >>= SHIFT_KG + time_constant;
ltemp = -ltemp;
} else {
ltemp = time_offset;
- ltemp <<= SHIFT_USEC - SHIFT_UPDATE;
+ ltemp <<= SHIFT_USEC - SHIFT_HZ;
+ ltemp = ltemp * HZ / 1000;
ltemp >>= SHIFT_KG + time_constant;
}

Index: linux-2.6-mm/include/linux/timex.h
===================================================================
--- linux-2.6-mm.orig/include/linux/timex.h 2005-12-21 12:12:00.000000000 +0100
+++ linux-2.6-mm/include/linux/timex.h 2005-12-21 12:12:08.000000000 +0100
@@ -95,11 +95,11 @@
#define SHIFT_USEC 16 /* frequency offset scale (shift) */
#define FINENSEC (1L << SHIFT_SCALE) /* ~1 ns in phase units */

-#define MAXPHASE 512000L /* max phase error (us) */
+#define MAXPHASE 500000000L /* max phase error (ns) */
#define MAXFREQ (512L << SHIFT_USEC) /* max frequency error (ppm) */
#define MINSEC 16L /* min interval between updates (s) */
#define MAXSEC 1200L /* max interval between updates (s) */
-#define NTP_PHASE_LIMIT (MAXPHASE << 5) /* beyond max. dispersion */
+#define NTP_PHASE_LIMIT ((MAXPHASE / 1000) << 5) /* beyond max. dispersion */

/*
* syscall interface - used (mainly by NTP daemon)
@@ -206,7 +206,7 @@ extern int tickadj; /* amount of adjus
*/
extern int time_state; /* clock status */
extern int time_status; /* clock synchronization status bits */
-extern long time_offset; /* time adjustment (us) */
+extern long time_offset; /* time adjustment (ns) */
extern long time_constant; /* pll time constant */
extern long time_tolerance; /* frequency tolerance (ppm) */
extern long time_precision; /* clock precision (us) */
Index: linux-2.6-mm/kernel/time.c
===================================================================
--- linux-2.6-mm.orig/kernel/time.c 2005-12-21 12:12:04.000000000 +0100
+++ linux-2.6-mm/kernel/time.c 2005-12-21 12:12:08.000000000 +0100
@@ -212,6 +212,7 @@ void __attribute__ ((weak)) notify_arch_
int do_adjtimex(struct timex *txc)
{
long ltemp, mtemp, save_adjust;
+ s64 freq_adj;
int result;

/* In order to modify anything, you gotta be super-user! */
@@ -227,7 +228,8 @@ int do_adjtimex(struct timex *txc)

if (txc->modes != ADJ_OFFSET_SINGLESHOT && (txc->modes & ADJ_OFFSET))
/* adjustment Offset limited to +- .512 seconds */
- if (txc->offset <= - MAXPHASE || txc->offset >= MAXPHASE )
+ if (txc->offset <= -MAXPHASE / 1000 ||
+ txc->offset >= MAXPHASE / 1000)
return -EINVAL;

/* if the quartz is off by more than 10% something is VERY wrong ! */
@@ -291,18 +293,18 @@ int do_adjtimex(struct timex *txc)
time_adjust = 0;
}
else if (time_status & STA_PLL) {
- ltemp = txc->offset;
+ ltemp = txc->offset * 1000;

/*
* Scale the phase adjustment and
* clamp to the operating range.
*/
if (ltemp > MAXPHASE)
- time_offset = MAXPHASE << SHIFT_UPDATE;
+ time_offset = MAXPHASE;
else if (ltemp < -MAXPHASE)
- time_offset = -(MAXPHASE << SHIFT_UPDATE);
+ time_offset = -MAXPHASE;
else
- time_offset = ltemp << SHIFT_UPDATE;
+ time_offset = ltemp;

/*
* Select whether the frequency is to be controlled
@@ -316,15 +318,21 @@ int do_adjtimex(struct timex *txc)
time_reftime = xtime.tv_sec;
if (time_status & STA_FLL) {
if (mtemp >= MINSEC) {
- ltemp = (time_offset / mtemp) << (SHIFT_USEC -
- SHIFT_UPDATE);
- time_freq += shift_right(ltemp, SHIFT_KH);
+ if (time_offset < 0) {
+ freq_adj = (s64)-time_offset << SHIFT_USEC;
+ do_div(freq_adj, mtemp);
+ time_freq -= freq_adj >> SHIFT_KH;
+ } else {
+ freq_adj = (s64)time_offset << SHIFT_USEC;
+ do_div(freq_adj, mtemp);
+ time_freq += freq_adj >> SHIFT_KH;
+ }
} else /* calibration interval too short (p. 12) */
result = TIME_ERROR;
} else { /* PLL mode */
if (mtemp < MAXSEC) {
- ltemp *= mtemp;
- time_freq += shift_right(ltemp,(time_constant +
+ freq_adj = (s64)ltemp * mtemp;
+ time_freq += shift_right(freq_adj,(time_constant +
time_constant +
SHIFT_KF - SHIFT_USEC));
} else /* calibration interval too long (p. 12) */
@@ -332,6 +340,7 @@ int do_adjtimex(struct timex *txc)
}
time_freq = min(time_freq, time_tolerance);
time_freq = max(time_freq, -time_tolerance);
+ time_offset = (time_offset / HZ) << SHIFT_HZ;
} /* STA_PLL */
} /* txc->modes & ADJ_OFFSET */
if (txc->modes & ADJ_TICK)
@@ -345,9 +354,8 @@ leave: if ((time_status & (STA_UNSYNC|ST

if ((txc->modes & ADJ_OFFSET_SINGLESHOT) == ADJ_OFFSET_SINGLESHOT)
txc->offset = save_adjust;
- else {
- txc->offset = shift_right(time_offset, SHIFT_UPDATE);
- }
+ else
+ txc->offset = shift_right(time_offset, SHIFT_HZ) * HZ / 1000;
txc->freq = time_freq;
txc->maxerror = time_maxerror;
txc->esterror = time_esterror;
Index: linux-2.6-mm/kernel/timer.c
===================================================================
--- linux-2.6-mm.orig/kernel/timer.c 2005-12-21 12:12:04.000000000 +0100
+++ linux-2.6-mm/kernel/timer.c 2005-12-21 12:12:08.000000000 +0100
@@ -577,7 +577,7 @@ int tickadj = 500/HZ ? : 1; /* microsec
/* TIME_ERROR prevents overwriting the CMOS clock */
int time_state = TIME_OK; /* clock synchronization status */
int time_status = STA_UNSYNC; /* clock status bits */
-long time_offset; /* time adjustment (us) */
+long time_offset; /* time adjustment (ns) */
long time_constant = 2; /* pll time constant */
long time_tolerance = MAXFREQ; /* frequency tolerance (ppm) */
long time_precision = 1; /* clock precision (us) */
@@ -606,6 +606,7 @@ void ntp_clear(void)

tick_nsec_curr = tick_nsec;
time_adj_curr = time_adj;
+ time_offset = 0;
}

void ntp_update_frequency(void)
@@ -646,7 +647,7 @@ void ntp_update_frequency(void)
*/
static void second_overflow(void)
{
- long ltemp, adj;
+ long ltemp;

/* Bump the maxerror field */
time_maxerror += time_tolerance >> SHIFT_USEC;
@@ -716,42 +717,33 @@ static void second_overflow(void)
* adjustment for each second is clamped so as to spread the adjustment
* over not more than the number of seconds between updates.
*/
- ltemp = time_offset;
- if (!(time_status & STA_FLL))
- ltemp = shift_right(ltemp, SHIFT_KG + time_constant);
- ltemp = min(ltemp, (MAXPHASE / MINSEC) << SHIFT_UPDATE);
- ltemp = max(ltemp, -(MAXPHASE / MINSEC) << SHIFT_UPDATE);
- time_offset -= ltemp;
- adj = ltemp << (SHIFT_SCALE - SHIFT_HZ - SHIFT_UPDATE);
-
- /*
- * Compute the frequency estimate and additional phase adjustment due
- * to frequency error for the next second.
- */
-
-#if HZ == 100
- /*
- * Compensate for (HZ==100) != (1 << SHIFT_HZ). Add 25% and 3.125% to
- * get 128.125; => only 0.125% error (p. 14)
- */
- adj += shift_right(adj, 2) + shift_right(adj, 5);
-#endif
-#if HZ == 250
- /*
- * Compensate for (HZ==250) != (1 << SHIFT_HZ). Add 1.5625% and
- * 0.78125% to get 255.85938; => only 0.05% error (p. 14)
- */
- adj += shift_right(adj, 6) + shift_right(adj, 7);
-#endif
-#if HZ == 1000
- /*
- * Compensate for (HZ==1000) != (1 << SHIFT_HZ). Add 1.5625% and
- * 0.78125% to get 1023.4375; => only 0.05% error (p. 14)
- */
- adj += shift_right(adj, 6) + shift_right(adj, 7);
-#endif
- tick_nsec_curr += adj >> (SHIFT_SCALE - 10);
- time_adj_curr += (adj << 10) & (FINENSEC - 1);
+ if (time_offset < 0) {
+ ltemp = -time_offset;
+ if (!(time_status & STA_FLL))
+ ltemp >>= SHIFT_KG + time_constant;
+ if (ltemp > (((MAXPHASE / HZ) << SHIFT_HZ) / MINSEC))
+ ltemp = ((MAXPHASE / HZ) << SHIFT_HZ) / MINSEC;
+ time_offset += ltemp;
+ tick_nsec_curr -= ltemp >> SHIFT_HZ;
+ time_adj_curr -= (ltemp << (SHIFT_SCALE - SHIFT_HZ)) & (FINENSEC - 1);
+ if (time_adj_curr < 0) {
+ tick_nsec_curr--;
+ time_adj_curr += FINENSEC;
+ }
+ } else {
+ ltemp = time_offset;
+ if (!(time_status & STA_FLL))
+ ltemp >>= SHIFT_KG + time_constant;
+ if (ltemp > (((MAXPHASE / HZ) << SHIFT_HZ) / MINSEC))
+ ltemp = ((MAXPHASE / HZ) << SHIFT_HZ) / MINSEC;
+ time_offset -= ltemp;
+ tick_nsec_curr += ltemp >> SHIFT_HZ;
+ time_adj_curr += (ltemp << (SHIFT_SCALE - SHIFT_HZ)) & (FINENSEC - 1);
+ if (time_adj_curr >= FINENSEC) {
+ tick_nsec_curr++;
+ time_adj_curr -= FINENSEC;
+ }
+ }
}

/* in the NTP reference this is called "hardclock()" */
-
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Next message: Roman Zippel: "[PATCH 6/10] NTP: add time_adjust to tick_nsec"
Previous message: James Bottomley: "Re: [GIT PATCH] SCSI bug fixes for 2.6.15-rc6"
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