ntp: increase time_freq resolution
This changes time_freq to a 64bit value and makes it static (the only outside
user had no real need to modify it). Intermediate values were already 64bit,
so the change isn't that big, but it saves a little in shifts by replacing
SHIFT_NSEC with TICK_LENGTH_SHIFT. PPM_SCALE is then used to convert between
user space and kernel space representation.
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>
diff --git a/arch/powerpc/kernel/time.c b/arch/powerpc/kernel/time.c
index 3b26fbd6..c146af9 100644
--- a/arch/powerpc/kernel/time.c
+++ b/arch/powerpc/kernel/time.c
@@ -1007,8 +1007,6 @@
vdso_data->stamp_xsec = (u64) xtime.tv_sec * XSEC_PER_SEC;
vdso_data->tb_to_xs = tb_to_xs;
- time_freq = 0;
-
write_sequnlock_irqrestore(&xtime_lock, flags);
/* Register the clocksource, if we're not running on iSeries */
diff --git a/include/linux/timex.h b/include/linux/timex.h
index 3c49d17..48c3376 100644
--- a/include/linux/timex.h
+++ b/include/linux/timex.h
@@ -86,11 +86,14 @@
*/
#define SHIFT_UPDATE (SHIFT_HZ + 1) /* time offset scale (shift) */
#define SHIFT_USEC 16 /* frequency offset scale (shift) */
-#define SHIFT_NSEC 12 /* kernel frequency offset scale */
+#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 MAXFREQ (512L << SHIFT_USEC) /* max frequency error (ppm) */
-#define MAXFREQ_NSEC (512000L << SHIFT_NSEC) /* max frequency error (ppb) */
+#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 */
@@ -209,8 +212,6 @@
extern long time_maxerror; /* maximum error */
extern long time_esterror; /* estimated error */
-extern long time_freq; /* frequency offset (scaled ppm) */
-
extern long time_adjust; /* The amount of adjtime left */
extern void ntp_clear(void);
diff --git a/kernel/time/ntp.c b/kernel/time/ntp.c
index 3fc8106..c6ae0c2 100644
--- a/kernel/time/ntp.c
+++ b/kernel/time/ntp.c
@@ -39,7 +39,7 @@
static long time_constant = 2; /* pll time constant */
long time_maxerror = NTP_PHASE_LIMIT; /* maximum error (us) */
long time_esterror = NTP_PHASE_LIMIT; /* estimated error (us) */
-long time_freq; /* frequency offset (scaled ppm)*/
+static s64 time_freq; /* frequency offset (scaled ns/s)*/
static long time_reftime; /* time at last adjustment (s) */
long time_adjust;
static long ntp_tick_adj;
@@ -49,7 +49,7 @@
u64 second_length = (u64)(tick_usec * NSEC_PER_USEC * USER_HZ)
<< TICK_LENGTH_SHIFT;
second_length += (s64)ntp_tick_adj << TICK_LENGTH_SHIFT;
- second_length += (s64)time_freq << (TICK_LENGTH_SHIFT - SHIFT_NSEC);
+ second_length += time_freq;
tick_length_base = second_length;
@@ -86,16 +86,16 @@
time_reftime = xtime.tv_sec;
freq_adj = time_offset * mtemp;
- freq_adj = shift_right(freq_adj, time_constant * 2 +
- (SHIFT_PLL + 2) * 2 - SHIFT_NSEC);
+ 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 << (SHIFT_NSEC - SHIFT_FLL), mtemp);
+ freq_adj += div_s64(time_offset << (TICK_LENGTH_SHIFT - SHIFT_FLL),
+ mtemp);
time_status |= STA_MODE;
}
freq_adj += time_freq;
- freq_adj = min(freq_adj, (s64)MAXFREQ_NSEC);
- time_freq = max(freq_adj, (s64)-MAXFREQ_NSEC);
+ 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;
}
@@ -131,7 +131,7 @@
long time_adj;
/* Bump the maxerror field */
- time_maxerror += MAXFREQ >> SHIFT_USEC;
+ time_maxerror += MAXFREQ / NSEC_PER_USEC;
if (time_maxerror > NTP_PHASE_LIMIT) {
time_maxerror = NTP_PHASE_LIMIT;
time_status |= STA_UNSYNC;
@@ -323,10 +323,9 @@
time_status &= ~STA_NANO;
if (txc->modes & ADJ_FREQUENCY) {
- time_freq = min(txc->freq, MAXFREQ);
- time_freq = min(time_freq, -MAXFREQ);
- time_freq = ((s64)time_freq * NSEC_PER_USEC)
- >> (SHIFT_USEC - SHIFT_NSEC);
+ time_freq = (s64)txc->freq * PPM_SCALE;
+ time_freq = min(time_freq, MAXFREQ_SCALED);
+ time_freq = max(time_freq, -MAXFREQ_SCALED);
}
if (txc->modes & ADJ_MAXERROR)
@@ -369,14 +368,15 @@
if (!(time_status & STA_NANO))
txc->offset /= NSEC_PER_USEC;
}
- txc->freq = (time_freq / NSEC_PER_USEC) <<
- (SHIFT_USEC - SHIFT_NSEC);
+ txc->freq = shift_right((s32)(time_freq >> PPM_SCALE_INV_SHIFT) *
+ (s64)PPM_SCALE_INV,
+ TICK_LENGTH_SHIFT);
txc->maxerror = time_maxerror;
txc->esterror = time_esterror;
txc->status = time_status;
txc->constant = time_constant;
txc->precision = 1;
- txc->tolerance = MAXFREQ;
+ txc->tolerance = MAXFREQ_SCALED / PPM_SCALE;
txc->tick = tick_usec;
/* PPS is not implemented, so these are zero */