From 9f14f669d18477fe3df071e2fa4da36c00acee8e Mon Sep 17 00:00:00 2001 From: Roman Zippel Date: Thu, 1 May 2008 04:34:36 -0700 Subject: [PATCH] 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 Cc: john stultz Cc: Thomas Gleixner Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- include/linux/timex.h | 9 ++------- kernel/time/ntp.c | 23 +++++++++++------------ 2 files changed, 13 insertions(+), 19 deletions(-) diff --git a/include/linux/timex.h b/include/linux/timex.h index 48c3376dce71..9fbdd12a52f1 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 c6ae0c249891..44491de312a0 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; } -- 2.20.1