Module: xenomai-gch
Branch: for-forge
Commit: a88858a4565e92e6084592c64bfc1ac218cc3c5a
URL:
http://git.xenomai.org/?p=xenomai-gch.git;a=commit;h=a88858a4565e92e6084592c64bfc1ac218cc3c5a
Author: Gilles Chanteperdrix <gilles.chanteperd...@xenomai.org>
Date: Sun Jun 1 16:51:59 2014 +0200
cobalt/timers: avoid periodic timer drift
Because timer period is converted to clock ticks when starting a periodic
timer, round-off errors may accumulate at each timer tick causing the timer
to drift. Fix this by keeping the timer period as a count of nanoseconds and
convert to clock ticks at each period. This adds some overhead, but is more
correct.
---
include/cobalt/kernel/timer.h | 60 ++++++++++++++++++++++++++++++-----------
kernel/cobalt/clock.c | 37 ++++++++++++++-----------
kernel/cobalt/posix/timer.c | 6 ++---
kernel/cobalt/posix/timerfd.c | 2 +-
kernel/cobalt/thread.c | 2 +-
kernel/cobalt/timer.c | 44 +++++++++---------------------
6 files changed, 82 insertions(+), 69 deletions(-)
diff --git a/include/cobalt/kernel/timer.h b/include/cobalt/kernel/timer.h
index 3c04cd0..7b4f36e 100644
--- a/include/cobalt/kernel/timer.h
+++ b/include/cobalt/kernel/timer.h
@@ -188,10 +188,14 @@ struct xntimer {
struct list_head adjlink;
/** Timer status. */
unsigned long status;
- /** Periodic interval (raw ticks, 0 == one shot). */
- xnticks_t interval;
- /** Date of next periodic release point (raw ticks). */
- xnticks_t pexpect;
+ /** Periodic interval (nanoseconds, 0 == one shot). */
+ xnticks_t interval_ns;
+ /** Count of timer ticks in periodic mode. */
+ xnticks_t periodic_ticks;
+ /** First tick date in periodic mode. */
+ xnticks_t start_date;
+ /** Date of next periodic release point (timer ticks). */
+ xnticks_t pexpect_ticks;
/** Sched structure to which the timer is attached. */
struct xnsched *sched;
/** Timeout handler. */
@@ -255,20 +259,19 @@ static inline xntimerq_t *xntimer_this_queue(struct
xntimer *timer)
return &tmd->q;
}
-static inline xnticks_t xntimer_interval(struct xntimer *timer)
+static inline void xntimer_update_date(struct xntimer *timer)
{
- return timer->interval;
-}
+ xntimerh_date(&timer->aplink) = timer->start_date +
+ xnclock_ns_to_ticks(xntimer_clock(timer),
+ timer->periodic_ticks * timer->interval_ns);
-static inline xnticks_t xntimer_pexpect(struct xntimer *timer)
-{
- return timer->pexpect;
}
-static inline xnticks_t xntimer_pexpect_forward(struct xntimer *timer,
- xnticks_t delta)
+static inline xnticks_t xntimer_pexpect(struct xntimer *timer)
{
- return timer->pexpect += delta;
+ return timer->start_date +
+ xnclock_ns_to_ticks(xntimer_clock(timer),
+ timer->pexpect_ticks * timer->interval_ns);
}
static inline void xntimer_set_priority(struct xntimer *timer,
@@ -292,6 +295,11 @@ static inline int xntimer_fired_p(struct xntimer *timer)
return (timer->status & XNTIMER_FIRED) != 0;
}
+static inline int xntimer_periodic_p(struct xntimer *timer)
+{
+ return (timer->status & XNTIMER_PERIODIC) != 0;
+}
+
static inline int xntimer_reload_p(struct xntimer *timer)
{
return (timer->status &
@@ -368,10 +376,30 @@ void xntimer_destroy(struct xntimer *timer);
* \addtogroup timer
*@{ */
+/**
+ * @fn xnticks_t xntimer_interval(struct xntimer *timer)
+ *
+ * @brief Return the timer interval value.
+ *
+ * Return the timer interval value in nanoseconds.
+ *
+ * @param timer The address of a valid timer descriptor.
+ *
+ * @return The duration of a period in nanoseconds. The special value
+ * XN_INFINITE is returned if @a timer is currently disabled or
+ * one shot.
+ *
+ * @remark Tags: isr-allowed.
+ */
+static inline xnticks_t xntimer_interval(struct xntimer *timer)
+{
+ return timer->interval_ns;
+}
+
int xntimer_start(struct xntimer *timer,
- xnticks_t value,
- xnticks_t interval,
- xntmode_t mode);
+ xnticks_t value,
+ xnticks_t interval,
+ xntmode_t mode);
void __xntimer_stop(struct xntimer *timer);
diff --git a/kernel/cobalt/clock.c b/kernel/cobalt/clock.c
index a2553d1..81b73a4 100644
--- a/kernel/cobalt/clock.c
+++ b/kernel/cobalt/clock.c
@@ -200,17 +200,19 @@ static void adjust_timer(struct xntimer *timer,
xntimerq_t *q,
xnsticks_t delta)
{
struct xnclock *clock = xntimer_clock(timer);
- xnticks_t period, mod;
+ xnticks_t period, div;
xnsticks_t diff;
xntimerh_date(&timer->aplink) -= delta;
- if ((timer->status & XNTIMER_PERIODIC) == 0)
+ if (xntimer_periodic_p(timer) == 0)
goto enqueue;
+ timer->start_date -= delta;
period = xntimer_interval(timer);
- timer->pexpect -= delta;
- diff = xnclock_read_raw(clock) - xntimerh_date(&timer->aplink);
+ diff = xnclock_ticks_to_ns(clock,
+ xnclock_read_raw(clock) -
+ xntimerh_date(&timer->aplink));
if ((xnsticks_t) (diff - period) >= 0) {
/*
@@ -220,8 +222,9 @@ static void adjust_timer(struct xntimer *timer, xntimerq_t
*q,
* that timer will tick only once and the lost ticks
* will be counted as overruns.
*/
- mod = xnarch_mod64(diff, period);
- xntimerh_date(&timer->aplink) += diff - mod;
+ div = xnarch_div64(diff, period);
+ timer->periodic_ticks += div;
+ xntimer_update_date(timer);
} else if (delta < 0
&& (timer->status & XNTIMER_FIRED)
&& (xnsticks_t) (diff + period) <= 0) {
@@ -232,9 +235,10 @@ static void adjust_timer(struct xntimer *timer, xntimerq_t
*q,
* time to a sooner date, real-time periodic timers do
* not tick until the original date has passed.
*/
- mod = xnarch_mod64(-diff, period);
- xntimerh_date(&timer->aplink) += diff + mod;
- timer->pexpect += diff + mod;
+ div = xnarch_div64(-diff, period);
+ timer->periodic_ticks -= div;
+ timer->pexpect_ticks -= div;
+ xntimer_update_date(timer);
}
enqueue:
@@ -383,7 +387,7 @@ static int clock_vfile_next(struct
xnvfile_snapshot_iterator *it, void *data)
p->scheduled = xnstat_counter_get(&timer->scheduled);
p->fired = xnstat_counter_get(&timer->fired);
p->timeout = xntimer_get_timeout(timer);
- p->interval = xntimer_get_interval(timer);
+ p->interval = xntimer_interval(timer);
p->status = timer->status;
knamecpy(p->handler, timer->handler_name);
knamecpy(p->name, timer->name);
@@ -551,7 +555,7 @@ void xnclock_tick(struct xnclock *clock)
{
xntimerq_t *timerq = &xnclock_this_timerdata(clock)->q;
struct xnsched *sched = xnsched_current();
- xnticks_t now, interval;
+ xnticks_t now, interval_ns;
struct xntimer *timer;
xnsticks_t delta;
xntimerh_t *h;
@@ -617,7 +621,7 @@ void xnclock_tick(struct xnclock *clock)
* wait for 250 ms for the user to continue
* program execution.
*/
- interval = xnclock_ns_to_ticks(clock, 250000000ULL);
+ interval_ns = 250000000ULL;
goto requeue;
}
fire:
@@ -632,11 +636,12 @@ void xnclock_tick(struct xnclock *clock)
if (!xntimer_reload_p(timer))
continue;
advance:
- interval = timer->interval;
+ interval_ns = timer->interval_ns;
requeue:
- do
- xntimerh_date(&timer->aplink) += interval;
- while (xntimerh_date(&timer->aplink) < now + clock->gravity);
+ do {
+ ++timer->periodic_ticks;
+ xntimer_update_date(timer);
+ } while (xntimerh_date(&timer->aplink) < now + clock->gravity);
#ifdef CONFIG_SMP
/*
* Make sure to pick the right percpu queue, in case
diff --git a/kernel/cobalt/posix/timer.c b/kernel/cobalt/posix/timer.c
index 476ea77..aa335ab 100644
--- a/kernel/cobalt/posix/timer.c
+++ b/kernel/cobalt/posix/timer.c
@@ -121,7 +121,7 @@ cobalt_timer_by_id(struct cobalt_process *cc, timer_t
timer_id)
if (test_bit(timer_id, cc->timers_map))
return NULL;
-
+
return cc->timers[timer_id];
}
@@ -185,7 +185,7 @@ static inline int timer_create(clockid_t clockid,
timer = xnmalloc(sizeof(*timer));
if (timer == NULL)
return -ENOMEM;
-
+
timer->sigp.si.si_errno = 0;
timer->sigp.si.si_code = SI_TIMER;
timer->sigp.si.si_overrun = 0;
@@ -667,7 +667,7 @@ int cobalt_timer_deliver(timer_t timerid) /* nklocked, IRQs
off. */
/* Killed before ultimate delivery, who cares then? */
return 0;
- if (!xntimer_interval(&timer->timerbase))
+ if (!xntimer_periodic_p(&timer->timerbase))
timer->overruns = 0;
else {
now = xnclock_read_raw(xntimer_clock(&timer->timerbase));
diff --git a/kernel/cobalt/posix/timerfd.c b/kernel/cobalt/posix/timerfd.c
index 3ffd8de..ebc554c 100644
--- a/kernel/cobalt/posix/timerfd.c
+++ b/kernel/cobalt/posix/timerfd.c
@@ -77,7 +77,7 @@ static ssize_t timerfd_read(struct rtdm_fd *fd, void __user
*buf, size_t size)
if (err == 0) {
xnticks_t now;
- if (xntimer_interval(&tfd->timer)) {
+ if (xntimer_periodic_p(&tfd->timer)) {
now = xnclock_read_raw(xntimer_clock(&tfd->timer));
ticks = 1 + xntimer_get_overruns(&tfd->timer, now);
} else
diff --git a/kernel/cobalt/thread.c b/kernel/cobalt/thread.c
index 5887be9..e3e9f44 100644
--- a/kernel/cobalt/thread.c
+++ b/kernel/cobalt/thread.c
@@ -340,7 +340,7 @@ xnticks_t xnthread_get_period(struct xnthread *thread)
* - or zero, meaning "no periodic activity".
*/
if (xntimer_running_p(&thread->ptimer))
- period = xntimer_get_interval(&thread->ptimer);
+ period = xntimer_interval(&thread->ptimer);
else if (xnthread_test_state(thread,XNRRB))
period = xnthread_time_slice(thread);
diff --git a/kernel/cobalt/timer.c b/kernel/cobalt/timer.c
index ac3aa9f..6bdc426 100644
--- a/kernel/cobalt/timer.c
+++ b/kernel/cobalt/timer.c
@@ -137,10 +137,12 @@ int xntimer_start(struct xntimer *timer,
xntimerh_date(&timer->aplink) = date;
- timer->interval = XN_INFINITE;
+ timer->interval_ns = XN_INFINITE;
if (interval != XN_INFINITE) {
- timer->interval = xnclock_ns_to_ticks(clock, interval);
- timer->pexpect = date;
+ timer->interval_ns = interval;
+ timer->periodic_ticks = 0;
+ timer->start_date = date;
+ timer->pexpect_ticks = 0;
timer->status |= XNTIMER_PERIODIC;
}
@@ -256,29 +258,6 @@ xnticks_t xntimer_get_timeout(struct xntimer *timer)
EXPORT_SYMBOL_GPL(xntimer_get_timeout);
/**
- * @fn xnticks_t xntimer_get_interval(struct xntimer *timer)
- *
- * @brief Return the timer interval value.
- *
- * Return the timer interval value in nanoseconds.
- *
- * @param timer The address of a valid timer descriptor.
- *
- * @return The duration of a period in nanoseconds. The special value
- * XN_INFINITE is returned if @a timer is currently disabled or
- * one shot.
- *
- * @remark Tags: isr-allowed.
- */
-xnticks_t xntimer_get_interval(struct xntimer *timer)
-{
- struct xnclock *clock = xntimer_clock(timer);
-
- return xnclock_ticks_to_ns_rounded(clock, timer->interval);
-}
-EXPORT_SYMBOL_GPL(xntimer_get_interval);
-
-/**
* @fn void xntimer_init(struct xntimer *timer,struct xnclock *clock,void
(*handler)(struct xntimer *timer), struct xnthread *thread)
* @brief Initialize a timer object.
*
@@ -329,7 +308,7 @@ void __xntimer_init(struct xntimer *timer,
xntimer_set_priority(timer, XNTIMER_STDPRIO);
timer->status = XNTIMER_DEQUEUED;
timer->handler = handler;
- timer->interval = 0;
+ timer->interval_ns = 0;
/*
* Timers have to run on a real-time CPU, i.e. a member of the
* xnsched_realtime_cpus mask. If the new timer is affine to a
@@ -366,7 +345,7 @@ void xntimer_switch_tracking(struct xntimer *timer,
{
struct xnclock *oldclock = timer->tracker;
spl_t s;
-
+
xnlock_get_irqsave(&nklock, s);
list_del(&timer->next_stat);
oldclock->nrtimers--;
@@ -486,16 +465,17 @@ void xntimer_release_ipi(void)
*/
unsigned long long xntimer_get_overruns(struct xntimer *timer, xnticks_t now)
{
- xnticks_t period = xntimer_interval(timer);
- xnsticks_t delta = now - timer->pexpect;
+ xnticks_t period = timer->interval_ns;
+ xnsticks_t delta;
unsigned long long overruns = 0;
+ delta = now - xntimer_pexpect(timer);
if (unlikely(delta >= (xnsticks_t) period)) {
overruns = xnarch_div64(delta, period);
- timer->pexpect += period * overruns;
+ timer->pexpect_ticks += overruns;
}
- timer->pexpect += period;
+ timer->pexpect_ticks++;
return overruns;
}
EXPORT_SYMBOL_GPL(xntimer_get_overruns);
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