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sam3x8e: Rework timer priority code to use time instead of event count 

Rework the timer prioritization code so that is compares against the
current time instead of the number of repeat timers in a given
interrupt.  This makes the code slightly faster and it should provide
better protection against task starvation.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>
This commit is contained in:
Kevin O'Connor 2016-10-31 11:48:27 -04:00
parent 233a90ce8b
commit 77d486f8d2
1 changed files with 15 additions and 12 deletions
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27
src/sam3x8e/timer.c
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@ -89,12 +89,12 @@ timer_set_next(uint32_t next)
return 1; return 1;
} }
static uint32_t timer_repeat; static uint32_t timer_repeat_until;
#define TIMER_MAX_REPEAT 400 #define TIMER_IDLE_REPEAT_TICKS timer_from_us(500)
#define TIMER_MAX_NEXT_REPEAT 150 #define TIMER_REPEAT_TICKS timer_from_us(100)
#define TIMER_MIN_TRY_TICKS timer_from_us(1) #define TIMER_MIN_TRY_TICKS timer_from_us(1)
#define TIMER_DEFER_REPEAT_TICKS timer_from_us(2) #define TIMER_DEFER_REPEAT_TICKS timer_from_us(5)
// Similar to timer_set_next(), but wait for the given time if it is // Similar to timer_set_next(), but wait for the given time if it is
// in the near future. // in the near future.
@ -108,10 +108,9 @@ timer_try_set_next(uint32_t next)
goto done; goto done;
// Next timer is in the past or near future - can't reschedule to it // Next timer is in the past or near future - can't reschedule to it
uint32_t tr = timer_repeat-1; if (likely(sched_is_before(now, timer_repeat_until))) {
if (likely(tr)) { // Can run more timers from this irq; briefly allow irqs
irq_enable(); irq_enable();
timer_repeat = tr;
while (diff >= 0) { while (diff >= 0) {
// Next timer is in the near future - wait for time to occur // Next timer is in the near future - wait for time to occur
now = timer_read_time(); now = timer_read_time();
@ -120,13 +119,13 @@ timer_try_set_next(uint32_t next)
irq_disable(); irq_disable();
return 0; return 0;
} }
// Too many repeat timers from a single interrupt - force a pause
timer_repeat = TIMER_MAX_NEXT_REPEAT;
next = now + TIMER_DEFER_REPEAT_TICKS;
if (diff < (int32_t)(-timer_from_us(1000))) if (diff < (int32_t)(-timer_from_us(1000)))
goto fail; goto fail;
// Too many repeat timers from a single interrupt - force a pause
timer_repeat_until = now + TIMER_REPEAT_TICKS;
next = now + TIMER_DEFER_REPEAT_TICKS;
done: done:
timer_set(next); timer_set(next);
return 1; return 1;
@ -134,9 +133,13 @@ fail:
shutdown("Rescheduled timer in the past"); shutdown("Rescheduled timer in the past");
} }
// Periodic background task that temporarily boosts priority of
// timers. This helps prioritize timers when tasks are idling.
static void static void
timer_task(void) timer_task(void)
{ {
timer_repeat = TIMER_MAX_REPEAT; irq_disable();
timer_repeat_until = timer_read_time() + TIMER_IDLE_REPEAT_TICKS;
irq_enable();
} }
DECL_TASK(timer_task); DECL_TASK(timer_task);