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linux: Avoid calling timer_read_time() in timer_dispatch() when not needed 

The timer_read_time() call can be expensive - when the next timer is
definitely pending, avoid making that call.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>
This commit is contained in:
Kevin O'Connor 2021-04-17 20:05:51 -04:00
parent 89af88d016
commit db0fb5d596
1 changed files with 15 additions and 3 deletions
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18
src/linux/timer.c
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@ -100,11 +100,15 @@ timer_is_before(uint32_t time1, uint32_t time2)
return (int32_t)(time1 - time2) < 0; return (int32_t)(time1 - time2) < 0;
} }
static uint32_t last_timer_read_time;
// Return the current time (in clock ticks) // Return the current time (in clock ticks)
uint32_t uint32_t
timer_read_time(void) timer_read_time(void)
{ {
return timespec_to_time(timespec_read()); uint32_t t = timespec_to_time(timespec_read());
last_timer_read_time = t;
return t;
} }
// Activate timer dispatch as soon as possible // Activate timer dispatch as soon as possible
@ -126,11 +130,19 @@ static uint32_t timer_repeat_until;
static uint32_t static uint32_t
timer_dispatch_many(void) timer_dispatch_many(void)
{ {
uint32_t tru = timer_repeat_until; uint32_t tru = timer_repeat_until, prev_ltrt = 0;
for (;;) { for (;;) {
// Run the next software timer // Run the next software timer
uint32_t next = sched_timer_dispatch(); uint32_t next = sched_timer_dispatch();
uint32_t ltrt = last_timer_read_time;
if (!timer_is_before(ltrt, next) && !timer_is_before(tru, ltrt)
&& ltrt != prev_ltrt) {
// Can run next timer without overhead of calling timer_read_time()
prev_ltrt = ltrt;
continue;
}
uint32_t now = timer_read_time(); uint32_t now = timer_read_time();
int32_t diff = next - now; int32_t diff = next - now;
if (diff > (int32_t)TIMER_MIN_TRY_TICKS) if (diff > (int32_t)TIMER_MIN_TRY_TICKS)
@ -158,7 +170,7 @@ timer_dispatch_many(void)
void void
timer_task(void) timer_task(void)
{ {
uint32_t now = timer_read_time(); uint32_t now = last_timer_read_time;
irq_disable(); irq_disable();
if (timer_is_before(timer_repeat_until, now)) if (timer_is_before(timer_repeat_until, now))
timer_repeat_until = now; timer_repeat_until = now;