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authorRoman Zippel <zippel@linux-m68k.org>2008-05-01 04:34:36 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2008-05-01 08:03:58 -0700
commit9f14f669d18477fe3df071e2fa4da36c00acee8e (patch)
tree84b5600017902ced77ee0cb9a4bc21a6768d22e5
parent074b3b87941c99bc0ce35385b5817924b1ed0c23 (diff)
ntp: 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> Cc: john stultz <johnstul@us.ibm.com> Cc: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--include/linux/timex.h9
-rw-r--r--kernel/time/ntp.c23
2 files changed, 13 insertions, 19 deletions
diff --git a/include/linux/timex.h b/include/linux/timex.h
index 48c3376dce7..9fbdd12a52f 100644
--- a/include/linux/timex.h
+++ b/include/linux/timex.h
@@ -76,27 +76,22 @@
#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)
diff --git a/kernel/time/ntp.c b/kernel/time/ntp.c
index c6ae0c24989..44491de312a 100644
--- a/kernel/time/ntp.c
+++ b/kernel/time/ntp.c
@@ -65,16 +65,15 @@ static void ntp_update_offset(long offset)
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 offset)
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;
}