lkml.org 
[lkml]   [2008]   [Mar]   [14]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
Subject[PATCH 4/8] increase time_offset resolution
time_offset is already a 64bit value but its resolution barely used, so
this makes better use of it by replacing SHIFT_UPDATE with
TICK_LENGTH_SHIFT.
Side note: the SHIFT_HZ in SHIFT_UPDATE was incorrect for CONFIG_NO_HZ
and the primary reason for changing time_offset to 64bit to avoid the
overflow.

Signed-off-by: Roman Zippel <zippel@linux-m68k.org>

---
include/linux/timex.h | 9 ++-------
kernel/time/ntp.c | 23 +++++++++++------------
2 files changed, 13 insertions(+), 19 deletions(-)

Index: linux-2.6-mm/include/linux/timex.h
===================================================================
--- linux-2.6-mm.orig/include/linux/timex.h
+++ linux-2.6-mm/include/linux/timex.h
@@ -74,27 +74,22 @@
#define MAXTC 10 /* maximum time constant (shift) */

/*
- * The SHIFT_UPDATE define establishes the decimal point of the
- * time_offset variable which represents the current offset with
- * respect to standard time.
- *
* SHIFT_USEC defines the scaling (shift) of the time_freq and
* time_tolerance variables, which represent the current frequency
* offset and maximum frequency tolerance.
*/
-#define SHIFT_UPDATE (SHIFT_HZ + 1) /* time offset scale (shift) */
#define SHIFT_USEC 16 /* frequency offset scale (shift) */
#define PPM_SCALE (NSEC_PER_USEC << (TICK_LENGTH_SHIFT - SHIFT_USEC))
#define PPM_SCALE_INV_SHIFT 20
#define PPM_SCALE_INV ((1ll << (PPM_SCALE_INV_SHIFT + TICK_LENGTH_SHIFT)) / \
PPM_SCALE + 1)

-#define MAXPHASE 512000L /* max phase error (us) */
+#define MAXPHASE 500000000l /* max phase error (ns) */
#define MAXFREQ 500000 /* max frequency error (ns/s) */
#define MAXFREQ_SCALED ((s64)MAXFREQ << TICK_LENGTH_SHIFT)
#define MINSEC 256 /* min interval between updates (s) */
#define MAXSEC 2048 /* max interval between updates (s) */
-#define NTP_PHASE_LIMIT (MAXPHASE << 5) /* beyond max. dispersion */
+#define NTP_PHASE_LIMIT ((MAXPHASE / NSEC_PER_USEC) << 5) /* beyond max. dispersion */

/*
* syscall interface - used (mainly by NTP daemon)
Index: linux-2.6-mm/kernel/time/ntp.c
===================================================================
--- linux-2.6-mm.orig/kernel/time/ntp.c
+++ linux-2.6-mm/kernel/time/ntp.c
@@ -65,16 +65,15 @@ static void ntp_update_offset(long offse
if (!(time_status & STA_PLL))
return;

- time_offset = offset;
if (!(time_status & STA_NANO))
- time_offset *= NSEC_PER_USEC;
+ offset *= NSEC_PER_USEC;

/*
* Scale the phase adjustment and
* clamp to the operating range.
*/
- time_offset = min(time_offset, (s64)MAXPHASE * NSEC_PER_USEC);
- time_offset = max(time_offset, (s64)-MAXPHASE * NSEC_PER_USEC);
+ offset = min(offset, MAXPHASE);
+ offset = max(offset, -MAXPHASE);

/*
* Select how the frequency is to be controlled
@@ -85,19 +84,19 @@ static void ntp_update_offset(long offse
mtemp = xtime.tv_sec - time_reftime;
time_reftime = xtime.tv_sec;

- freq_adj = time_offset * mtemp;
+ freq_adj = (s64)offset * mtemp;
freq_adj <<= TICK_LENGTH_SHIFT - 2 * (SHIFT_PLL + 2 + time_constant);
time_status &= ~STA_MODE;
if (mtemp >= MINSEC && (time_status & STA_FLL || mtemp > MAXSEC)) {
- freq_adj += div_s64(time_offset << (TICK_LENGTH_SHIFT - SHIFT_FLL),
+ freq_adj += div_s64((s64)offset << (TICK_LENGTH_SHIFT - SHIFT_FLL),
mtemp);
time_status |= STA_MODE;
}
freq_adj += time_freq;
freq_adj = min(freq_adj, MAXFREQ_SCALED);
time_freq = max(freq_adj, -MAXFREQ_SCALED);
- time_offset = div_s64(time_offset, NTP_INTERVAL_FREQ);
- time_offset <<= SHIFT_UPDATE;
+
+ time_offset = div_s64((s64)offset << TICK_LENGTH_SHIFT, NTP_INTERVAL_FREQ);
}

/**
@@ -128,7 +127,7 @@ void ntp_clear(void)
*/
void second_overflow(void)
{
- long time_adj;
+ s64 time_adj;

/* Bump the maxerror field */
time_maxerror += MAXFREQ / NSEC_PER_USEC;
@@ -184,7 +183,7 @@ void second_overflow(void)
tick_length = tick_length_base;
time_adj = shift_right(time_offset, SHIFT_PLL + time_constant);
time_offset -= time_adj;
- tick_length += (s64)time_adj << (TICK_LENGTH_SHIFT - SHIFT_UPDATE);
+ tick_length += time_adj;

if (unlikely(time_adjust)) {
if (time_adjust > MAX_TICKADJ) {
@@ -363,8 +362,8 @@ int do_adjtimex(struct timex *txc)
(txc->modes == ADJ_OFFSET_SS_READ))
txc->offset = save_adjust;
else {
- txc->offset = ((long)shift_right(time_offset, SHIFT_UPDATE)) *
- NTP_INTERVAL_FREQ;
+ txc->offset = shift_right(time_offset * NTP_INTERVAL_FREQ,
+ TICK_LENGTH_SHIFT);
if (!(time_status & STA_NANO))
txc->offset /= NSEC_PER_USEC;
}
--



\
 
 \ /
  Last update: 2008-03-14 21:05    [W:0.090 / U:33.524 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site