diff options
| -rw-r--r-- | include/linux/clocksource.h | 97 | ||||
| -rw-r--r-- | kernel/timer.c | 47 |
2 files changed, 125 insertions, 19 deletions
diff --git a/include/linux/clocksource.h b/include/linux/clocksource.h index c4187cda0ee4..c4739c4e3039 100644 --- a/include/linux/clocksource.h +++ b/include/linux/clocksource.h @@ -173,6 +173,103 @@ static inline void calculate_clocksource_interval(struct clocksource *c, c->interval_snsecs = (u64)c->interval_cycles * c->mult; } + +/** + * error_aproximation - calculates an error adjustment for a given error + * + * @error: Error value (unsigned) + * @unit: Adjustment unit + * + * For a given error value, this function takes the adjustment unit + * and uses binary approximation to return a power of two adjustment value. + * + * This function is only for use by the the make_ntp_adj() function + * and you must hold a write on the xtime_lock when calling. + */ +static inline int error_aproximation(u64 error, u64 unit) +{ + static int saved_adj = 0; + u64 adjusted_unit = unit << saved_adj; + + if (error > (adjusted_unit * 2)) { + /* large error, so increment the adjustment factor */ + saved_adj++; + } else if (error > adjusted_unit) { + /* just right, don't touch it */ + } else if (saved_adj) { + /* small error, so drop the adjustment factor */ + saved_adj--; + return 0; + } + + return saved_adj; +} + + +/** + * make_ntp_adj - Adjusts the specified clocksource for a given error + * + * @clock: Pointer to clock to be adjusted + * @cycles_delta: Current unacounted cycle delta + * @error: Pointer to current error value + * + * Returns clock shifted nanosecond adjustment to be applied against + * the accumulated time value (ie: xtime). + * + * If the error value is large enough, this function calulates the + * (power of two) adjustment value, and adjusts the clock's mult and + * interval_snsecs values accordingly. + * + * However, since there may be some unaccumulated cycles, to avoid + * time inconsistencies we must adjust the accumulation value + * accordingly. + * + * This is not very intuitive, so the following proof should help: + * The basic timeofday algorithm: base + cycle * mult + * Thus: + * new_base + cycle * new_mult = old_base + cycle * old_mult + * new_base = old_base + cycle * old_mult - cycle * new_mult + * new_base = old_base + cycle * (old_mult - new_mult) + * new_base - old_base = cycle * (old_mult - new_mult) + * base_delta = cycle * (old_mult - new_mult) + * base_delta = cycle * (mult_delta) + * + * Where mult_delta is the adjustment value made to mult + * + */ +static inline s64 make_ntp_adj(struct clocksource *clock, + cycles_t cycles_delta, s64* error) +{ + s64 ret = 0; + if (*error > ((s64)clock->interval_cycles+1)/2) { + /* calculate adjustment value */ + int adjustment = error_aproximation(*error, + clock->interval_cycles); + /* adjust clock */ + clock->mult += 1 << adjustment; + clock->interval_snsecs += clock->interval_cycles << adjustment; + + /* adjust the base and error for the adjustment */ + ret = -(cycles_delta << adjustment); + *error -= clock->interval_cycles << adjustment; + /* XXX adj error for cycle_delta offset? */ + } else if ((-(*error)) > ((s64)clock->interval_cycles+1)/2) { + /* calculate adjustment value */ + int adjustment = error_aproximation(-(*error), + clock->interval_cycles); + /* adjust clock */ + clock->mult -= 1 << adjustment; + clock->interval_snsecs -= clock->interval_cycles << adjustment; + + /* adjust the base and error for the adjustment */ + ret = cycles_delta << adjustment; + *error += clock->interval_cycles << adjustment; + /* XXX adj error for cycle_delta offset? */ + } + return ret; +} + + /* used to install a new clocksource */ int register_clocksource(struct clocksource*); void reselect_clocksource(void); diff --git a/kernel/timer.c b/kernel/timer.c index 623f9ea198d8..6811436a031d 100644 --- a/kernel/timer.c +++ b/kernel/timer.c @@ -597,7 +597,6 @@ long time_tolerance = MAXFREQ; /* frequency tolerance (ppm) */ long time_precision = 1; /* clock precision (us) */ long time_maxerror = NTP_PHASE_LIMIT; /* maximum error (us) */ long time_esterror = NTP_PHASE_LIMIT; /* estimated error (us) */ -static long time_phase; /* phase offset (scaled us) */ long time_freq = (((NSEC_PER_SEC + HZ/2) % HZ - HZ/2) << SHIFT_USEC) / NSEC_PER_USEC; /* frequency offset (scaled ppm)*/ static long time_adj; /* tick adjust (scaled 1 / HZ) */ @@ -747,27 +746,14 @@ static long adjtime_adjustment(void) } /* in the NTP reference this is called "hardclock()" */ -static void update_wall_time_one_tick(void) +static void update_ntp_one_tick(void) { - long time_adjust_step, delta_nsec; + long time_adjust_step; time_adjust_step = adjtime_adjustment(); if (time_adjust_step) /* Reduce by this step the amount of time left */ time_adjust -= time_adjust_step; - delta_nsec = tick_nsec + time_adjust_step * 1000; - /* - * Advance the phase, once it gets to one microsecond, then - * advance the tick more. - */ - time_phase += time_adj; - if ((time_phase >= FINENSEC) || (time_phase <= -FINENSEC)) { - long ltemp = shift_right(time_phase, (SHIFT_SCALE - 10)); - time_phase -= ltemp << (SHIFT_SCALE - 10); - delta_nsec += ltemp; - } - xtime.tv_nsec += delta_nsec; - time_interpolator_update(delta_nsec); /* Changes by adjtime() do not take effect till next tick. */ if (time_next_adjust != 0) { @@ -872,8 +858,13 @@ device_initcall(timekeeping_init_device); */ static void update_wall_time(void) { + static s64 remainder_snsecs, error; + s64 snsecs_per_sec; cycle_t now, offset; + snsecs_per_sec = (s64)NSEC_PER_SEC << clock->shift; + remainder_snsecs += (s64)xtime.tv_nsec << clock->shift; + now = read_clocksource(clock); offset = (now - last_clock_cycle)&clock->mask; @@ -881,17 +872,35 @@ static void update_wall_time(void) * case of lost or late ticks, it will accumulate correctly. */ while (offset > clock->interval_cycles) { + /* get the ntp interval in clock shifted nanoseconds */ + s64 ntp_snsecs = current_tick_length(clock->shift); + /* accumulate one interval */ + remainder_snsecs += clock->interval_snsecs; last_clock_cycle += clock->interval_cycles; offset -= clock->interval_cycles; - update_wall_time_one_tick(); - if (xtime.tv_nsec >= 1000000000) { - xtime.tv_nsec -= 1000000000; + /* interpolator bits */ + time_interpolator_update(clock->interval_snsecs + >> clock->shift); + /* increment the NTP state machine */ + update_ntp_one_tick(); + + /* accumulate error between NTP and clock interval */ + error += (ntp_snsecs - (s64)clock->interval_snsecs); + + /* correct the clock when NTP error is too big */ + remainder_snsecs += make_ntp_adj(clock, offset, &error); + + if (remainder_snsecs >= snsecs_per_sec) { + remainder_snsecs -= snsecs_per_sec; xtime.tv_sec++; second_overflow(); } } + /* store full nanoseconds into xtime */ + xtime.tv_nsec = remainder_snsecs >> clock->shift; + remainder_snsecs -= (s64)xtime.tv_nsec << clock->shift; } /* |