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Make _cyclic_ timers interval more deterministic - next timeout is calculated from last due time instead of relative to current time

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This eliminates the cyclic timer jitter
This commit is contained in:
Dirk Ziegelmeier
2018-01-05 13:45:51 +01:00
parent 2b4dde84e3
commit eaca067c7d
3 changed files with 100 additions and 62 deletions
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38
src/core/timeouts.c
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@@ -67,7 +67,7 @@
#endif /* LWIP_DEBUG_TIMERNAMES */
/* Check if timer's expiry time is greater than time and care about u32_t wraparounds */
#define TIMER_LESS_THAN(timer, t) ( (((timer)->time == (t)) || (((u32_t)((timer)->time-(t))) > 0x7fffffff)) ? 1 : 0 )
#define TIME_LESS_THAN(t, compare_to) ( (((t) == (compare_to)) || (((u32_t)((t)-(compare_to))) > 0x7fffffff)) ? 1 : 0 )
/** This array contains all stack-internal cyclic timers. To get the number of
* timers, use LWIP_ARRAYSIZE() */
@@ -115,6 +115,8 @@ const int lwip_num_cyclic_timers = LWIP_ARRAYSIZE(lwip_cyclic_timers);
/** The one and only timeout list */
static struct sys_timeo *next_timeout;
static u32_t current_timeout_due_time;
#if LWIP_TESTMODE
struct sys_timeo**
lwip_sys_timers_get_next_timout(void)
@@ -173,15 +175,30 @@ tcp_timer_needed(void)
*
* @param arg unused argument
*/
static void
cyclic_timer(void *arg)
#if !LWIP_TESTMODE
static
#endif
void
lwip_cyclic_timer(void *arg)
{
u32_t now;
u32_t next_timeout;
const struct lwip_cyclic_timer *cyclic = (const struct lwip_cyclic_timer *)arg;
#if LWIP_DEBUG_TIMERNAMES
LWIP_DEBUGF(TIMERS_DEBUG, ("tcpip: %s()\n", cyclic->handler_name));
#endif
cyclic->handler();
sys_timeout(cyclic->interval_ms, cyclic_timer, arg);
now = sys_now();
next_timeout = (u32_t)(current_timeout_due_time + cyclic->interval_ms);
if (TIME_LESS_THAN(next_timeout, now)) {
/* timer would immediately expire again -> "overload" -> restart without any correction */
sys_timeout(cyclic->interval_ms, lwip_cyclic_timer, arg);
} else {
/* correct cyclic interval with handler execution delay and sys_check_timeouts jitter */
sys_timeout((u32_t)(next_timeout - now), lwip_cyclic_timer, arg);
}
}
/** Initialize this module */
@@ -192,7 +209,7 @@ void sys_timeouts_init(void)
for (i = (LWIP_TCP ? 1 : 0); i < LWIP_ARRAYSIZE(lwip_cyclic_timers); i++) {
/* we have to cast via size_t to get rid of const warning
(this is OK as cyclic_timer() casts back to const* */
sys_timeout(lwip_cyclic_timers[i].interval_ms, cyclic_timer, LWIP_CONST_CAST(void *, &lwip_cyclic_timers[i]));
sys_timeout(lwip_cyclic_timers[i].interval_ms, lwip_cyclic_timer, LWIP_CONST_CAST(void *, &lwip_cyclic_timers[i]));
}
}
@@ -230,7 +247,7 @@ sys_timeout(u32_t msecs, sys_timeout_handler handler, void *arg)
timeout->next = NULL;
timeout->h = handler;
timeout->arg = arg;
timeout->time = (u32_t)(now + msecs); /* overflow handled by TIMER_LESS_THAN macro */
timeout->time = (u32_t)(now + msecs); /* overflow handled by TIME_LESS_THAN macro */
#if LWIP_DEBUG_TIMERNAMES
timeout->handler_name = handler_name;
LWIP_DEBUGF(TIMERS_DEBUG, ("sys_timeout: %p msecs=%"U32_F" handler=%s arg=%p\n",
@@ -241,12 +258,12 @@ sys_timeout(u32_t msecs, sys_timeout_handler handler, void *arg)
next_timeout = timeout;
return;
}
if (TIMER_LESS_THAN(timeout, next_timeout->time)) {
if (TIME_LESS_THAN(timeout->time, next_timeout->time)) {
timeout->next = next_timeout;
next_timeout = timeout;
} else {
for (t = next_timeout; t != NULL; t = t->next) {
if ((t->next == NULL) || TIMER_LESS_THAN(timeout, t->next->time)) {
if ((t->next == NULL) || TIME_LESS_THAN(timeout->time, t->next->time)) {
timeout->next = t->next;
t->next = timeout;
break;
@@ -322,12 +339,13 @@ sys_check_timeouts(void)
had_one = 0;
tmptimeout = next_timeout;
now = sys_now();
if (tmptimeout && TIMER_LESS_THAN(tmptimeout, now)) {
if (tmptimeout && TIME_LESS_THAN(tmptimeout->time, now)) {
/* timeout has expired */
had_one = 1;
next_timeout = tmptimeout->next;
handler = tmptimeout->h;
arg = tmptimeout->arg;
current_timeout_due_time = tmptimeout->time;
#if LWIP_DEBUG_TIMERNAMES
if (handler != NULL) {
LWIP_DEBUGF(TIMERS_DEBUG, ("sct calling h=%s arg=%p\n",
@@ -373,7 +391,7 @@ sys_timeouts_sleeptime(void)
return 0xffffffff;
}
now = sys_now();
if (TIMER_LESS_THAN(next_timeout, now)) {
if (TIME_LESS_THAN(next_timeout->time, now)) {
return 0;
} else {
return (u32_t)(next_timeout->time - now);