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Merge branch 'timers-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 

* 'timers-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  hrtimer: Fix extra wakeups from __remove_hrtimer()
  timekeeping: add arch_offset hook to ktime_get functions
  clocksource: Avoid selecting mult values that might overflow when adjusted
  time: Improve documentation of timekeeeping_adjust()
This commit is contained in:
Linus Torvalds 2011-11-28 08:43:52 -08:00
parent ce8f55c2a0 27c9cd7e60
commit c28800a9c3
4 changed files with 145 additions and 14 deletions
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3
include/linux/clocksource.h
View File

@ -156,6 +156,7 @@ extern u64 timecounter_cyc2time(struct timecounter *tc,
* @mult: cycle to nanosecond multiplier
* @shift: cycle to nanosecond divisor (power of two)
* @max_idle_ns: max idle time permitted by the clocksource (nsecs)
* @maxadj maximum adjustment value to mult (~11%)
* @flags: flags describing special properties
* @archdata: arch-specific data
* @suspend: suspend function for the clocksource, if necessary
@ -172,7 +173,7 @@ struct clocksource {
u32 mult;
u32 shift;
u64 max_idle_ns;
u32 maxadj;
#ifdef CONFIG_ARCH_CLOCKSOURCE_DATA
struct arch_clocksource_data archdata;
#endif

6
kernel/hrtimer.c
View File

@ -885,10 +885,13 @@ static void __remove_hrtimer(struct hrtimer *timer,
struct hrtimer_clock_base *base,
unsigned long newstate, int reprogram)
{
struct timerqueue_node *next_timer;
if (!(timer->state & HRTIMER_STATE_ENQUEUED))
goto out;
if (&timer->node == timerqueue_getnext(&base->active)) {
next_timer = timerqueue_getnext(&base->active);
timerqueue_del(&base->active, &timer->node);
if (&timer->node == next_timer) {
#ifdef CONFIG_HIGH_RES_TIMERS
/* Reprogram the clock event device. if enabled */
if (reprogram && hrtimer_hres_active()) {
@ -901,7 +904,6 @@ static void __remove_hrtimer(struct hrtimer *timer,
}
#endif
}
timerqueue_del(&base->active, &timer->node);
if (!timerqueue_getnext(&base->active))
base->cpu_base->active_bases &= ~(1 << base->index);
out:

58
kernel/time/clocksource.c
View File

@ -491,6 +491,22 @@ void clocksource_touch_watchdog(void)
clocksource_resume_watchdog();
}
/**
* clocksource_max_adjustment- Returns max adjustment amount
* @cs: Pointer to clocksource
*
*/
static u32 clocksource_max_adjustment(struct clocksource *cs)
{
u64 ret;
/*
* We won't try to correct for more then 11% adjustments (110,000 ppm),
*/
ret = (u64)cs->mult * 11;
do_div(ret,100);
return (u32)ret;
}
/**
* clocksource_max_deferment - Returns max time the clocksource can be deferred
* @cs: Pointer to clocksource
@ -503,25 +519,28 @@ static u64 clocksource_max_deferment(struct clocksource *cs)
/*
* Calculate the maximum number of cycles that we can pass to the
* cyc2ns function without overflowing a 64-bit signed result. The
* maximum number of cycles is equal to ULLONG_MAX/cs->mult which
* is equivalent to the below.
* max_cycles < (2^63)/cs->mult
* max_cycles < 2^(log2((2^63)/cs->mult))
* max_cycles < 2^(log2(2^63) - log2(cs->mult))
* max_cycles < 2^(63 - log2(cs->mult))
* max_cycles < 1 << (63 - log2(cs->mult))
* maximum number of cycles is equal to ULLONG_MAX/(cs->mult+cs->maxadj)
* which is equivalent to the below.
* max_cycles < (2^63)/(cs->mult + cs->maxadj)
* max_cycles < 2^(log2((2^63)/(cs->mult + cs->maxadj)))
* max_cycles < 2^(log2(2^63) - log2(cs->mult + cs->maxadj))
* max_cycles < 2^(63 - log2(cs->mult + cs->maxadj))
* max_cycles < 1 << (63 - log2(cs->mult + cs->maxadj))
* Please note that we add 1 to the result of the log2 to account for
* any rounding errors, ensure the above inequality is satisfied and
* no overflow will occur.
*/
max_cycles = 1ULL << (63 - (ilog2(cs->mult) + 1));
max_cycles = 1ULL << (63 - (ilog2(cs->mult + cs->maxadj) + 1));
/*
* The actual maximum number of cycles we can defer the clocksource is
* determined by the minimum of max_cycles and cs->mask.
* Note: Here we subtract the maxadj to make sure we don't sleep for
* too long if there's a large negative adjustment.
*/
max_cycles = min_t(u64, max_cycles, (u64) cs->mask);
max_nsecs = clocksource_cyc2ns(max_cycles, cs->mult, cs->shift);
max_nsecs = clocksource_cyc2ns(max_cycles, cs->mult - cs->maxadj,
cs->shift);
/*
* To ensure that the clocksource does not wrap whilst we are idle,
@ -640,7 +659,6 @@ static void clocksource_enqueue(struct clocksource *cs)
void __clocksource_updatefreq_scale(struct clocksource *cs, u32 scale, u32 freq)
{
u64 sec;
/*
* Calc the maximum number of seconds which we can run before
* wrapping around. For clocksources which have a mask > 32bit
@ -661,6 +679,20 @@ void __clocksource_updatefreq_scale(struct clocksource *cs, u32 scale, u32 freq)
clocks_calc_mult_shift(&cs->mult, &cs->shift, freq,
NSEC_PER_SEC / scale, sec * scale);
/*
* for clocksources that have large mults, to avoid overflow.
* Since mult may be adjusted by ntp, add an safety extra margin
*
*/
cs->maxadj = clocksource_max_adjustment(cs);
while ((cs->mult + cs->maxadj < cs->mult)
|| (cs->mult - cs->maxadj > cs->mult)) {
cs->mult >>= 1;
cs->shift--;
cs->maxadj = clocksource_max_adjustment(cs);
}
cs->max_idle_ns = clocksource_max_deferment(cs);
}
EXPORT_SYMBOL_GPL(__clocksource_updatefreq_scale);
@ -701,6 +733,12 @@ EXPORT_SYMBOL_GPL(__clocksource_register_scale);
*/
int clocksource_register(struct clocksource *cs)
{
/* calculate max adjustment for given mult/shift */
cs->maxadj = clocksource_max_adjustment(cs);
WARN_ONCE(cs->mult + cs->maxadj < cs->mult,
"Clocksource %s might overflow on 11%% adjustment\n",
cs->name);
/* calculate max idle time permitted for this clocksource */
cs->max_idle_ns = clocksource_max_deferment(cs);

92
kernel/time/timekeeping.c
View File

@ -249,6 +249,8 @@ ktime_t ktime_get(void)
secs = xtime.tv_sec + wall_to_monotonic.tv_sec;
nsecs = xtime.tv_nsec + wall_to_monotonic.tv_nsec;
nsecs += timekeeping_get_ns();
/* If arch requires, add in gettimeoffset() */
nsecs += arch_gettimeoffset();
} while (read_seqretry(&xtime_lock, seq));
/*
@ -280,6 +282,8 @@ void ktime_get_ts(struct timespec *ts)
*ts = xtime;
tomono = wall_to_monotonic;
nsecs = timekeeping_get_ns();
/* If arch requires, add in gettimeoffset() */
nsecs += arch_gettimeoffset();
} while (read_seqretry(&xtime_lock, seq));
@ -802,14 +806,44 @@ static void timekeeping_adjust(s64 offset)
s64 error, interval = timekeeper.cycle_interval;
int adj;
/*
* The point of this is to check if the error is greater then half
* an interval.
*
* First we shift it down from NTP_SHIFT to clocksource->shifted nsecs.
*
* Note we subtract one in the shift, so that error is really error*2.
* This "saves" dividing(shifting) intererval twice, but keeps the
* (error > interval) comparision as still measuring if error is
* larger then half an interval.
*
* Note: It does not "save" on aggrivation when reading the code.
*/
error = timekeeper.ntp_error >> (timekeeper.ntp_error_shift - 1);
if (error > interval) {
/*
* We now divide error by 4(via shift), which checks if
* the error is greater then twice the interval.
* If it is greater, we need a bigadjust, if its smaller,
* we can adjust by 1.
*/
error >>= 2;
/*
* XXX - In update_wall_time, we round up to the next
* nanosecond, and store the amount rounded up into
* the error. This causes the likely below to be unlikely.
*
* The properfix is to avoid rounding up by using
* the high precision timekeeper.xtime_nsec instead of
* xtime.tv_nsec everywhere. Fixing this will take some
* time.
*/
if (likely(error <= interval))
adj = 1;
else
adj = timekeeping_bigadjust(error, &interval, &offset);
} else if (error < -interval) {
/* See comment above, this is just switched for the negative */
error >>= 2;
if (likely(error >= -interval)) {
adj = -1;
@ -817,9 +851,65 @@ static void timekeeping_adjust(s64 offset)
offset = -offset;
} else
adj = timekeeping_bigadjust(error, &interval, &offset);
} else
} else /* No adjustment needed */
return;
WARN_ONCE(timekeeper.clock->maxadj &&
(timekeeper.mult + adj > timekeeper.clock->mult +
timekeeper.clock->maxadj),
"Adjusting %s more then 11%% (%ld vs %ld)\n",
timekeeper.clock->name, (long)timekeeper.mult + adj,
(long)timekeeper.clock->mult +
timekeeper.clock->maxadj);
/*
* So the following can be confusing.
*
* To keep things simple, lets assume adj == 1 for now.
*
* When adj != 1, remember that the interval and offset values
* have been appropriately scaled so the math is the same.
*
* The basic idea here is that we're increasing the multiplier
* by one, this causes the xtime_interval to be incremented by
* one cycle_interval. This is because:
* xtime_interval = cycle_interval * mult
* So if mult is being incremented by one:
* xtime_interval = cycle_interval * (mult + 1)
* Its the same as:
* xtime_interval = (cycle_interval * mult) + cycle_interval
* Which can be shortened to:
* xtime_interval += cycle_interval
*
* So offset stores the non-accumulated cycles. Thus the current
* time (in shifted nanoseconds) is:
* now = (offset * adj) + xtime_nsec
* Now, even though we're adjusting the clock frequency, we have
* to keep time consistent. In other words, we can't jump back
* in time, and we also want to avoid jumping forward in time.
*
* So given the same offset value, we need the time to be the same
* both before and after the freq adjustment.
* now = (offset * adj_1) + xtime_nsec_1
* now = (offset * adj_2) + xtime_nsec_2
* So:
* (offset * adj_1) + xtime_nsec_1 =
* (offset * adj_2) + xtime_nsec_2
* And we know:
* adj_2 = adj_1 + 1
* So:
* (offset * adj_1) + xtime_nsec_1 =
* (offset * (adj_1+1)) + xtime_nsec_2
* (offset * adj_1) + xtime_nsec_1 =
* (offset * adj_1) + offset + xtime_nsec_2
* Canceling the sides:
* xtime_nsec_1 = offset + xtime_nsec_2
* Which gives us:
* xtime_nsec_2 = xtime_nsec_1 - offset
* Which simplfies to:
* xtime_nsec -= offset
*
* XXX - TODO: Doc ntp_error calculation.
*/
timekeeper.mult += adj;
timekeeper.xtime_interval += interval;
timekeeper.xtime_nsec -= offset;