From e154ff3d2c5ad313ef0c66e6217502361cad2799 Mon Sep 17 00:00:00 2001 From: Roman Zippel Date: Mon, 10 Jul 2006 04:44:32 -0700 Subject: [PATCH] adjust clock for lost ticks A large number of lost ticks can cause an overadjustment of the clock. To compensate for this we look at the current error and the larger the error already is the more careful we are at adjusting the error. As small extra fix reset the error when the clock is set. Signed-off-by: Roman Zippel Acked-by: john stultz Cc: Uwe Bugla Cc: James Bottomley Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- kernel/timer.c | 85 ++++++++++++++++++++++++++++++++-------------------------- 1 file changed, 47 insertions(+), 38 deletions(-) (limited to 'kernel/timer.c') diff --git a/kernel/timer.c b/kernel/timer.c index 396a3c024c2c..2a87430a58d4 100644 --- a/kernel/timer.c +++ b/kernel/timer.c @@ -891,6 +891,7 @@ int do_settimeofday(struct timespec *tv) set_normalized_timespec(&xtime, sec, nsec); set_normalized_timespec(&wall_to_monotonic, wtm_sec, wtm_nsec); + clock->error = 0; ntp_clear(); write_sequnlock_irqrestore(&xtime_lock, flags); @@ -1008,52 +1009,52 @@ static int __init timekeeping_init_device(void) device_initcall(timekeeping_init_device); /* - * If the error is already larger, we look ahead another tick, + * If the error is already larger, we look ahead even further * to compensate for late or lost adjustments. */ -static __always_inline int clocksource_bigadjust(int sign, s64 error, s64 *interval, s64 *offset) +static __always_inline int clocksource_bigadjust(s64 error, s64 *interval, s64 *offset) { - int adj; + s64 tick_error, i; + u32 look_ahead, adj; + s32 error2, mult; /* - * As soon as the machine is synchronized to the external time - * source this should be the common case. + * Use the current error value to determine how much to look ahead. + * The larger the error the slower we adjust for it to avoid problems + * with losing too many ticks, otherwise we would overadjust and + * produce an even larger error. The smaller the adjustment the + * faster we try to adjust for it, as lost ticks can do less harm + * here. This is tuned so that an error of about 1 msec is adusted + * within about 1 sec (or 2^20 nsec in 2^SHIFT_HZ ticks). */ - error >>= 2; - if (likely(sign > 0 ? error <= *interval : error >= *interval)) - return sign; + error2 = clock->error >> (TICK_LENGTH_SHIFT + 22 - 2 * SHIFT_HZ); + error2 = abs(error2); + for (look_ahead = 0; error2 > 0; look_ahead++) + error2 >>= 2; /* - * An extra look ahead dampens the effect of the current error, - * which can grow quite large with continously late updates, as - * it would dominate the adjustment value and can lead to - * oscillation. + * Now calculate the error in (1 << look_ahead) ticks, but first + * remove the single look ahead already included in the error. */ - error += current_tick_length() >> (TICK_LENGTH_SHIFT - clock->shift + 1); - error -= clock->xtime_interval >> 1; - - adj = 0; - while (1) { - error >>= 1; - if (sign > 0 ? error <= *interval : error >= *interval) - break; - adj++; + tick_error = current_tick_length() >> (TICK_LENGTH_SHIFT - clock->shift + 1); + tick_error -= clock->xtime_interval >> 1; + error = ((error - tick_error) >> look_ahead) + tick_error; + + /* Finally calculate the adjustment shift value. */ + i = *interval; + mult = 1; + if (error < 0) { + error = -error; + *interval = -*interval; + *offset = -*offset; + mult = -1; } - - /* - * Add the current adjustments to the error and take the offset - * into account, the latter can cause the error to be hardly - * reduced at the next tick. Check the error again if there's - * room for another adjustment, thus further reducing the error - * which otherwise had to be corrected at the next update. - */ - error = (error << 1) - *interval + *offset; - if (sign > 0 ? error > *interval : error < *interval) - adj++; + for (adj = 0; error > i; adj++) + error >>= 1; *interval <<= adj; *offset <<= adj; - return sign << adj; + return mult << adj; } /* @@ -1068,11 +1069,19 @@ static void clocksource_adjust(struct clocksource *clock, s64 offset) error = clock->error >> (TICK_LENGTH_SHIFT - clock->shift - 1); if (error > interval) { - adj = clocksource_bigadjust(1, error, &interval, &offset); + error >>= 2; + if (likely(error <= interval)) + adj = 1; + else + adj = clocksource_bigadjust(error, &interval, &offset); } else if (error < -interval) { - interval = -interval; - offset = -offset; - adj = clocksource_bigadjust(-1, error, &interval, &offset); + error >>= 2; + if (likely(error >= -interval)) { + adj = -1; + interval = -interval; + offset = -offset; + } else + adj = clocksource_bigadjust(error, &interval, &offset); } else return; @@ -1129,7 +1138,7 @@ static void update_wall_time(void) clocksource_adjust(clock, offset); /* store full nanoseconds into xtime */ - xtime.tv_nsec = clock->xtime_nsec >> clock->shift; + xtime.tv_nsec = (s64)clock->xtime_nsec >> clock->shift; clock->xtime_nsec -= (s64)xtime.tv_nsec << clock->shift; /* check to see if there is a new clocksource to use */ -- cgit v1.2.3 From a0009652af385a42f0e0604136f772ead406c78d Mon Sep 17 00:00:00 2001 From: Andrew Morton Date: Fri, 14 Jul 2006 00:24:06 -0700 Subject: [PATCH] del_timer_sync(): add cpu_relax() Relax the CPU in the del_timer_sync() busywait loop. Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- kernel/timer.c | 1 + 1 file changed, 1 insertion(+) (limited to 'kernel/timer.c') diff --git a/kernel/timer.c b/kernel/timer.c index 2a87430a58d4..acfa557e685b 100644 --- a/kernel/timer.c +++ b/kernel/timer.c @@ -374,6 +374,7 @@ int del_timer_sync(struct timer_list *timer) int ret = try_to_del_timer_sync(timer); if (ret >= 0) return ret; + cpu_relax(); } } -- cgit v1.2.3 From 3e143475c22036847f898d7e76ba337c1d7dbf6f Mon Sep 17 00:00:00 2001 From: john stultz Date: Fri, 14 Jul 2006 00:24:17 -0700 Subject: [PATCH] improve timekeeping resume robustness Resolve problems seen w/ APM suspend. Due to resume initialization ordering, its possible we could get a timer interrupt before the timekeeping resume() function is called. This patch ensures we don't do any timekeeping accounting before we're fully resumed. (akpm: fixes the machine-freezes-on-APM-resume bug) Signed-off-by: John Stultz Cc: Roman Zippel Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- kernel/timer.c | 19 ++++++++++++++++++- 1 file changed, 18 insertions(+), 1 deletion(-) (limited to 'kernel/timer.c') diff --git a/kernel/timer.c b/kernel/timer.c index acfa557e685b..05809c2e2fd6 100644 --- a/kernel/timer.c +++ b/kernel/timer.c @@ -969,6 +969,7 @@ void __init timekeeping_init(void) } +static int timekeeping_suspended; /* * timekeeping_resume - Resumes the generic timekeeping subsystem. * @dev: unused @@ -984,6 +985,18 @@ static int timekeeping_resume(struct sys_device *dev) write_seqlock_irqsave(&xtime_lock, flags); /* restart the last cycle value */ clock->cycle_last = clocksource_read(clock); + clock->error = 0; + timekeeping_suspended = 0; + write_sequnlock_irqrestore(&xtime_lock, flags); + return 0; +} + +static int timekeeping_suspend(struct sys_device *dev, pm_message_t state) +{ + unsigned long flags; + + write_seqlock_irqsave(&xtime_lock, flags); + timekeeping_suspended = 1; write_sequnlock_irqrestore(&xtime_lock, flags); return 0; } @@ -991,6 +1004,7 @@ static int timekeeping_resume(struct sys_device *dev) /* sysfs resume/suspend bits for timekeeping */ static struct sysdev_class timekeeping_sysclass = { .resume = timekeeping_resume, + .suspend = timekeeping_suspend, set_kset_name("timekeeping"), }; @@ -1101,13 +1115,16 @@ static void update_wall_time(void) { cycle_t offset; - clock->xtime_nsec += (s64)xtime.tv_nsec << clock->shift; + /* Make sure we're fully resumed: */ + if (unlikely(timekeeping_suspended)) + return; #ifdef CONFIG_GENERIC_TIME offset = (clocksource_read(clock) - clock->cycle_last) & clock->mask; #else offset = clock->cycle_interval; #endif + clock->xtime_nsec += (s64)xtime.tv_nsec << clock->shift; /* normally this loop will run just once, however in the * case of lost or late ticks, it will accumulate correctly. -- cgit v1.2.3