+++ /dev/null
-Time Interpolators
-------------------
-
-Time interpolators are a base of time calculation between timer ticks and
-allow an accurate determination of time down to the accuracy of the time
-source in nanoseconds.
-
-The architecture specific code typically provides gettimeofday and
-settimeofday under Linux. The time interpolator provides both if an arch
-defines CONFIG_TIME_INTERPOLATION. The arch still must set up timer tick
-operations and call the necessary functions to advance the clock.
-
-With the time interpolator a standardized interface exists for time
-interpolation between ticks. The provided logic is highly scalable
-and has been tested in SMP situations of up to 512 CPUs.
-
-If CONFIG_TIME_INTERPOLATION is defined then the architecture specific code
-(or the device drivers - like HPET) may register time interpolators.
-These are typically defined in the following way:
-
-static struct time_interpolator my_interpolator {
- .frequency = MY_FREQUENCY,
- .source = TIME_SOURCE_MMIO32,
- .shift = 8, /* scaling for higher accuracy */
- .drift = -1, /* Unknown drift */
- .jitter = 0 /* time source is stable */
-};
-
-void time_init(void)
-{
- ....
- /* Initialization of the timer *.
- my_interpolator.address = &my_timer;
- register_time_interpolator(&my_interpolator);
- ....
-}
-
-For more details see include/linux/timex.h and kernel/timer.c.
-
-Christoph Lameter <christoph@lameter.com>, October 31, 2004
-
__x < 0 ? -(-__x >> __s) : __x >> __s; \
})
-
-#ifdef CONFIG_TIME_INTERPOLATION
-
-#define TIME_SOURCE_CPU 0
-#define TIME_SOURCE_MMIO64 1
-#define TIME_SOURCE_MMIO32 2
-#define TIME_SOURCE_FUNCTION 3
-
-/* For proper operations time_interpolator clocks must run slightly slower
- * than the standard clock since the interpolator may only correct by having
- * time jump forward during a tick. A slower clock is usually a side effect
- * of the integer divide of the nanoseconds in a second by the frequency.
- * The accuracy of the division can be increased by specifying a shift.
- * However, this may cause the clock not to be slow enough.
- * The interpolator will self-tune the clock by slowing down if no
- * resets occur or speeding up if the time jumps per analysis cycle
- * become too high.
- *
- * Setting jitter compensates for a fluctuating timesource by comparing
- * to the last value read from the timesource to insure that an earlier value
- * is not returned by a later call. The price to pay
- * for the compensation is that the timer routines are not as scalable anymore.
- */
-
-struct time_interpolator {
- u16 source; /* time source flags */
- u8 shift; /* increases accuracy of multiply by shifting. */
- /* Note that bits may be lost if shift is set too high */
- u8 jitter; /* if set compensate for fluctuations */
- u32 nsec_per_cyc; /* set by register_time_interpolator() */
- void *addr; /* address of counter or function */
- cycles_t mask; /* mask the valid bits of the counter */
- unsigned long offset; /* nsec offset at last update of interpolator */
- u64 last_counter; /* counter value in units of the counter at last update */
- cycles_t last_cycle; /* Last timer value if TIME_SOURCE_JITTER is set */
- u64 frequency; /* frequency in counts/second */
- long drift; /* drift in parts-per-million (or -1) */
- unsigned long skips; /* skips forward */
- unsigned long ns_skipped; /* nanoseconds skipped */
- struct time_interpolator *next;
-};
-
-extern void register_time_interpolator(struct time_interpolator *);
-extern void unregister_time_interpolator(struct time_interpolator *);
-extern void time_interpolator_reset(void);
-extern unsigned long time_interpolator_get_offset(void);
-extern void time_interpolator_update(long delta_nsec);
-
-#else /* !CONFIG_TIME_INTERPOLATION */
-
-static inline void time_interpolator_reset(void)
-{
-}
-
-static inline void time_interpolator_update(long delta_nsec)
-{
-}
-
-#endif /* !CONFIG_TIME_INTERPOLATION */
-
#define TICK_LENGTH_SHIFT 32
#ifdef CONFIG_NO_HZ
write_seqlock_irq(&xtime_lock);
wall_to_monotonic.tv_sec -= sys_tz.tz_minuteswest * 60;
xtime.tv_sec += sys_tz.tz_minuteswest * 60;
- time_interpolator_reset();
write_sequnlock_irq(&xtime_lock);
clock_was_set();
}
}
EXPORT_SYMBOL(timespec_trunc);
-#ifdef CONFIG_TIME_INTERPOLATION
-void getnstimeofday (struct timespec *tv)
-{
- unsigned long seq,sec,nsec;
-
- do {
- seq = read_seqbegin(&xtime_lock);
- sec = xtime.tv_sec;
- nsec = xtime.tv_nsec+time_interpolator_get_offset();
- } while (unlikely(read_seqretry(&xtime_lock, seq)));
-
- while (unlikely(nsec >= NSEC_PER_SEC)) {
- nsec -= NSEC_PER_SEC;
- ++sec;
- }
- tv->tv_sec = sec;
- tv->tv_nsec = nsec;
-}
-EXPORT_SYMBOL_GPL(getnstimeofday);
-
-int do_settimeofday (struct timespec *tv)
-{
- time_t wtm_sec, sec = tv->tv_sec;
- long wtm_nsec, nsec = tv->tv_nsec;
-
- if ((unsigned long)tv->tv_nsec >= NSEC_PER_SEC)
- return -EINVAL;
-
- write_seqlock_irq(&xtime_lock);
- {
- wtm_sec = wall_to_monotonic.tv_sec + (xtime.tv_sec - sec);
- wtm_nsec = wall_to_monotonic.tv_nsec + (xtime.tv_nsec - nsec);
-
- set_normalized_timespec(&xtime, sec, nsec);
- set_normalized_timespec(&wall_to_monotonic, wtm_sec, wtm_nsec);
-
- time_adjust = 0; /* stop active adjtime() */
- time_status |= STA_UNSYNC;
- time_maxerror = NTP_PHASE_LIMIT;
- time_esterror = NTP_PHASE_LIMIT;
- time_interpolator_reset();
- }
- write_sequnlock_irq(&xtime_lock);
- clock_was_set();
- return 0;
-}
-EXPORT_SYMBOL(do_settimeofday);
-
-void do_gettimeofday (struct timeval *tv)
-{
- unsigned long seq, nsec, usec, sec, offset;
- do {
- seq = read_seqbegin(&xtime_lock);
- offset = time_interpolator_get_offset();
- sec = xtime.tv_sec;
- nsec = xtime.tv_nsec;
- } while (unlikely(read_seqretry(&xtime_lock, seq)));
-
- usec = (nsec + offset) / 1000;
-
- while (unlikely(usec >= USEC_PER_SEC)) {
- usec -= USEC_PER_SEC;
- ++sec;
- }
-
- tv->tv_sec = sec;
- tv->tv_usec = usec;
-
- /*
- * Make sure xtime.tv_sec [returned by sys_time()] always
- * follows the gettimeofday() result precisely. This
- * condition is extremely unlikely, it can hit at most
- * once per second:
- */
- if (unlikely(xtime.tv_sec != tv->tv_sec)) {
- unsigned long flags;
-
- write_seqlock_irqsave(&xtime_lock, flags);
- update_wall_time();
- write_sequnlock_irqrestore(&xtime_lock, flags);
- }
-}
-EXPORT_SYMBOL(do_gettimeofday);
-
-#else /* CONFIG_TIME_INTERPOLATION */
-
#ifndef CONFIG_GENERIC_TIME
/*
* Simulate gettimeofday using do_gettimeofday which only allows a timeval
}
EXPORT_SYMBOL_GPL(getnstimeofday);
#endif
-#endif /* CONFIG_TIME_INTERPOLATION */
/* Converts Gregorian date to seconds since 1970-01-01 00:00:00.
* Assumes input in normal date format, i.e. 1980-12-31 23:59:59
if (xtime.tv_sec % 86400 == 0) {
xtime.tv_sec--;
wall_to_monotonic.tv_sec++;
- /*
- * The timer interpolator will make time change
- * gradually instead of an immediate jump by one second
- */
- time_interpolator_update(-NSEC_PER_SEC);
time_state = TIME_OOP;
printk(KERN_NOTICE "Clock: inserting leap second "
"23:59:60 UTC\n");
if ((xtime.tv_sec + 1) % 86400 == 0) {
xtime.tv_sec++;
wall_to_monotonic.tv_sec--;
- /*
- * Use of time interpolator for a gradual change of
- * time
- */
- time_interpolator_update(NSEC_PER_SEC);
time_state = TIME_WAIT;
printk(KERN_NOTICE "Clock: deleting leap second "
"23:59:59 UTC\n");
second_overflow();
}
- /* interpolator bits */
- time_interpolator_update(clock->xtime_interval
- >> clock->shift);
-
/* accumulate error between NTP and clock interval */
clock->error += current_tick_length();
clock->error -= clock->xtime_interval << (TICK_LENGTH_SHIFT - clock->shift);
open_softirq(TIMER_SOFTIRQ, run_timer_softirq, NULL);
}
-#ifdef CONFIG_TIME_INTERPOLATION
-
-struct time_interpolator *time_interpolator __read_mostly;
-static struct time_interpolator *time_interpolator_list __read_mostly;
-static DEFINE_SPINLOCK(time_interpolator_lock);
-
-static inline cycles_t time_interpolator_get_cycles(unsigned int src)
-{
- unsigned long (*x)(void);
-
- switch (src)
- {
- case TIME_SOURCE_FUNCTION:
- x = time_interpolator->addr;
- return x();
-
- case TIME_SOURCE_MMIO64 :
- return readq_relaxed((void __iomem *)time_interpolator->addr);
-
- case TIME_SOURCE_MMIO32 :
- return readl_relaxed((void __iomem *)time_interpolator->addr);
-
- default: return get_cycles();
- }
-}
-
-static inline u64 time_interpolator_get_counter(int writelock)
-{
- unsigned int src = time_interpolator->source;
-
- if (time_interpolator->jitter)
- {
- cycles_t lcycle;
- cycles_t now;
-
- do {
- lcycle = time_interpolator->last_cycle;
- now = time_interpolator_get_cycles(src);
- if (lcycle && time_after(lcycle, now))
- return lcycle;
-
- /* When holding the xtime write lock, there's no need
- * to add the overhead of the cmpxchg. Readers are
- * force to retry until the write lock is released.
- */
- if (writelock) {
- time_interpolator->last_cycle = now;
- return now;
- }
- /* Keep track of the last timer value returned. The use of cmpxchg here
- * will cause contention in an SMP environment.
- */
- } while (unlikely(cmpxchg(&time_interpolator->last_cycle, lcycle, now) != lcycle));
- return now;
- }
- else
- return time_interpolator_get_cycles(src);
-}
-
-void time_interpolator_reset(void)
-{
- time_interpolator->offset = 0;
- time_interpolator->last_counter = time_interpolator_get_counter(1);
-}
-
-#define GET_TI_NSECS(count,i) (((((count) - i->last_counter) & (i)->mask) * (i)->nsec_per_cyc) >> (i)->shift)
-
-unsigned long time_interpolator_get_offset(void)
-{
- /* If we do not have a time interpolator set up then just return zero */
- if (!time_interpolator)
- return 0;
-
- return time_interpolator->offset +
- GET_TI_NSECS(time_interpolator_get_counter(0), time_interpolator);
-}
-
-#define INTERPOLATOR_ADJUST 65536
-#define INTERPOLATOR_MAX_SKIP 10*INTERPOLATOR_ADJUST
-
-void time_interpolator_update(long delta_nsec)
-{
- u64 counter;
- unsigned long offset;
-
- /* If there is no time interpolator set up then do nothing */
- if (!time_interpolator)
- return;
-
- /*
- * The interpolator compensates for late ticks by accumulating the late
- * time in time_interpolator->offset. A tick earlier than expected will
- * lead to a reset of the offset and a corresponding jump of the clock
- * forward. Again this only works if the interpolator clock is running
- * slightly slower than the regular clock and the tuning logic insures
- * that.
- */
-
- counter = time_interpolator_get_counter(1);
- offset = time_interpolator->offset +
- GET_TI_NSECS(counter, time_interpolator);
-
- if (delta_nsec < 0 || (unsigned long) delta_nsec < offset)
- time_interpolator->offset = offset - delta_nsec;
- else {
- time_interpolator->skips++;
- time_interpolator->ns_skipped += delta_nsec - offset;
- time_interpolator->offset = 0;
- }
- time_interpolator->last_counter = counter;
-
- /* Tuning logic for time interpolator invoked every minute or so.
- * Decrease interpolator clock speed if no skips occurred and an offset is carried.
- * Increase interpolator clock speed if we skip too much time.
- */
- if (jiffies % INTERPOLATOR_ADJUST == 0)
- {
- if (time_interpolator->skips == 0 && time_interpolator->offset > tick_nsec)
- time_interpolator->nsec_per_cyc--;
- if (time_interpolator->ns_skipped > INTERPOLATOR_MAX_SKIP && time_interpolator->offset == 0)
- time_interpolator->nsec_per_cyc++;
- time_interpolator->skips = 0;
- time_interpolator->ns_skipped = 0;
- }
-}
-
-static inline int
-is_better_time_interpolator(struct time_interpolator *new)
-{
- if (!time_interpolator)
- return 1;
- return new->frequency > 2*time_interpolator->frequency ||
- (unsigned long)new->drift < (unsigned long)time_interpolator->drift;
-}
-
-void
-register_time_interpolator(struct time_interpolator *ti)
-{
- unsigned long flags;
-
- /* Sanity check */
- BUG_ON(ti->frequency == 0 || ti->mask == 0);
-
- ti->nsec_per_cyc = ((u64)NSEC_PER_SEC << ti->shift) / ti->frequency;
- spin_lock(&time_interpolator_lock);
- write_seqlock_irqsave(&xtime_lock, flags);
- if (is_better_time_interpolator(ti)) {
- time_interpolator = ti;
- time_interpolator_reset();
- }
- write_sequnlock_irqrestore(&xtime_lock, flags);
-
- ti->next = time_interpolator_list;
- time_interpolator_list = ti;
- spin_unlock(&time_interpolator_lock);
-}
-
-void
-unregister_time_interpolator(struct time_interpolator *ti)
-{
- struct time_interpolator *curr, **prev;
- unsigned long flags;
-
- spin_lock(&time_interpolator_lock);
- prev = &time_interpolator_list;
- for (curr = *prev; curr; curr = curr->next) {
- if (curr == ti) {
- *prev = curr->next;
- break;
- }
- prev = &curr->next;
- }
-
- write_seqlock_irqsave(&xtime_lock, flags);
- if (ti == time_interpolator) {
- /* we lost the best time-interpolator: */
- time_interpolator = NULL;
- /* find the next-best interpolator */
- for (curr = time_interpolator_list; curr; curr = curr->next)
- if (is_better_time_interpolator(curr))
- time_interpolator = curr;
- time_interpolator_reset();
- }
- write_sequnlock_irqrestore(&xtime_lock, flags);
- spin_unlock(&time_interpolator_lock);
-}
-#endif /* CONFIG_TIME_INTERPOLATION */
-
/**
* msleep - sleep safely even with waitqueue interruptions
* @msecs: Time in milliseconds to sleep for
git://ftp.safe.ca / safe / jmp / linux-2.6 / commitdiff