diff options
| -rw-r--r-- | include/linux/timekeeper_internal.h | 2 | ||||
| -rw-r--r-- | kernel/time/timekeeping.c | 138 |
2 files changed, 49 insertions, 91 deletions
diff --git a/include/linux/timekeeper_internal.h b/include/linux/timekeeper_internal.h index d315c3d6725c..7acb953298a7 100644 --- a/include/linux/timekeeper_internal.h +++ b/include/linux/timekeeper_internal.h @@ -117,6 +117,8 @@ struct timekeeper { s64 ntp_error; u32 ntp_error_shift; u32 ntp_err_mult; + /* Flag used to avoid updating NTP twice with same second */ + u32 skip_second_overflow; #ifdef CONFIG_DEBUG_TIMEKEEPING long last_warning; /* diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c index c1a0ac17336e..e11760121cb2 100644 --- a/kernel/time/timekeeping.c +++ b/kernel/time/timekeeping.c @@ -332,6 +332,7 @@ static void tk_setup_internals(struct timekeeper *tk, struct clocksource *clock) tk->tkr_mono.mult = clock->mult; tk->tkr_raw.mult = clock->mult; tk->ntp_err_mult = 0; + tk->skip_second_overflow = 0; } /* Timekeeper helper functions. */ @@ -1799,20 +1800,19 @@ device_initcall(timekeeping_init_ops); */ static __always_inline void timekeeping_apply_adjustment(struct timekeeper *tk, s64 offset, - bool negative, - int adj_scale) + s32 mult_adj) { s64 interval = tk->cycle_interval; - s32 mult_adj = 1; - if (negative) { - mult_adj = -mult_adj; + if (mult_adj == 0) { + return; + } else if (mult_adj == -1) { interval = -interval; - offset = -offset; + offset = -offset; + } else if (mult_adj != 1) { + interval *= mult_adj; + offset *= mult_adj; } - mult_adj <<= adj_scale; - interval <<= adj_scale; - offset <<= adj_scale; /* * So the following can be confusing. @@ -1873,85 +1873,35 @@ static __always_inline void timekeeping_apply_adjustment(struct timekeeper *tk, } /* - * Calculate the multiplier adjustment needed to match the frequency - * specified by NTP + * Adjust the timekeeper's multiplier to the correct frequency + * and also to reduce the accumulated error value. */ -static __always_inline void timekeeping_freqadjust(struct timekeeper *tk, - s64 offset) +static void timekeeping_adjust(struct timekeeper *tk, s64 offset) { - s64 interval = tk->cycle_interval; - s64 xinterval = tk->xtime_interval; - u32 base = tk->tkr_mono.clock->mult; - u32 max = tk->tkr_mono.clock->maxadj; - u32 cur_adj = tk->tkr_mono.mult; - s64 tick_error; - bool negative; - u32 adj_scale; - - /* Remove any current error adj from freq calculation */ - if (tk->ntp_err_mult) - xinterval -= tk->cycle_interval; - - tk->ntp_tick = ntp_tick_length(); - - /* Calculate current error per tick */ - tick_error = ntp_tick_length() >> tk->ntp_error_shift; - tick_error -= (xinterval + tk->xtime_remainder); - - /* Don't worry about correcting it if its small */ - if (likely((tick_error >= 0) && (tick_error <= interval))) - return; - - /* preserve the direction of correction */ - negative = (tick_error < 0); + u32 mult; - /* If any adjustment would pass the max, just return */ - if (negative && (cur_adj - 1) <= (base - max)) - return; - if (!negative && (cur_adj + 1) >= (base + max)) - return; /* - * Sort out the magnitude of the correction, but - * avoid making so large a correction that we go - * over the max adjustment. + * Determine the multiplier from the current NTP tick length. + * Avoid expensive division when the tick length doesn't change. */ - adj_scale = 0; - tick_error = abs(tick_error); - while (tick_error > interval) { - u32 adj = 1 << (adj_scale + 1); - - /* Check if adjustment gets us within 1 unit from the max */ - if (negative && (cur_adj - adj) <= (base - max)) - break; - if (!negative && (cur_adj + adj) >= (base + max)) - break; - - adj_scale++; - tick_error >>= 1; + if (likely(tk->ntp_tick == ntp_tick_length())) { + mult = tk->tkr_mono.mult - tk->ntp_err_mult; + } else { + tk->ntp_tick = ntp_tick_length(); + mult = div64_u64((tk->ntp_tick >> tk->ntp_error_shift) - + tk->xtime_remainder, tk->cycle_interval); } - /* scale the corrections */ - timekeeping_apply_adjustment(tk, offset, negative, adj_scale); -} + /* + * If the clock is behind the NTP time, increase the multiplier by 1 + * to catch up with it. If it's ahead and there was a remainder in the + * tick division, the clock will slow down. Otherwise it will stay + * ahead until the tick length changes to a non-divisible value. + */ + tk->ntp_err_mult = tk->ntp_error > 0 ? 1 : 0; + mult += tk->ntp_err_mult; -/* - * Adjust the timekeeper's multiplier to the correct frequency - * and also to reduce the accumulated error value. - */ -static void timekeeping_adjust(struct timekeeper *tk, s64 offset) -{ - /* Correct for the current frequency error */ - timekeeping_freqadjust(tk, offset); - - /* Next make a small adjustment to fix any cumulative error */ - if (!tk->ntp_err_mult && (tk->ntp_error > 0)) { - tk->ntp_err_mult = 1; - timekeeping_apply_adjustment(tk, offset, 0, 0); - } else if (tk->ntp_err_mult && (tk->ntp_error <= 0)) { - /* Undo any existing error adjustment */ - timekeeping_apply_adjustment(tk, offset, 1, 0); - tk->ntp_err_mult = 0; - } + timekeeping_apply_adjustment(tk, offset, mult - tk->tkr_mono.mult); if (unlikely(tk->tkr_mono.clock->maxadj && (abs(tk->tkr_mono.mult - tk->tkr_mono.clock->mult) @@ -1968,18 +1918,15 @@ static void timekeeping_adjust(struct timekeeper *tk, s64 offset) * in the code above, its possible the required corrective factor to * xtime_nsec could cause it to underflow. * - * Now, since we already accumulated the second, cannot simply roll - * the accumulated second back, since the NTP subsystem has been - * notified via second_overflow. So instead we push xtime_nsec forward - * by the amount we underflowed, and add that amount into the error. - * - * We'll correct this error next time through this function, when - * xtime_nsec is not as small. + * Now, since we have already accumulated the second and the NTP + * subsystem has been notified via second_overflow(), we need to skip + * the next update. */ if (unlikely((s64)tk->tkr_mono.xtime_nsec < 0)) { - s64 neg = -(s64)tk->tkr_mono.xtime_nsec; - tk->tkr_mono.xtime_nsec = 0; - tk->ntp_error += neg << tk->ntp_error_shift; + tk->tkr_mono.xtime_nsec += (u64)NSEC_PER_SEC << + tk->tkr_mono.shift; + tk->xtime_sec--; + tk->skip_second_overflow = 1; } } @@ -2002,6 +1949,15 @@ static inline unsigned int accumulate_nsecs_to_secs(struct timekeeper *tk) tk->tkr_mono.xtime_nsec -= nsecps; tk->xtime_sec++; + /* + * Skip NTP update if this second was accumulated before, + * i.e. xtime_nsec underflowed in timekeeping_adjust() + */ + if (unlikely(tk->skip_second_overflow)) { + tk->skip_second_overflow = 0; + continue; + } + /* Figure out if its a leap sec and apply if needed */ leap = second_overflow(tk->xtime_sec); if (unlikely(leap)) { @@ -2118,7 +2074,7 @@ void update_wall_time(void) shift--; } - /* correct the clock when NTP error is too big */ + /* Adjust the multiplier to correct NTP error */ timekeeping_adjust(tk, offset); /* |