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sched: improve time jump detection

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To detect forward time jumps, use a timestamp made before calling
select() instead of the first timeout in the queue. Also, if the timeout
value is modified by select() (e.g. on Linux) use it to get a more
accurate estimate of the elapsed time.
This commit is contained in:
Miroslav Lichvar 2014-08-20 11:34:16 +02:00
parent badf97d4ba
commit e63bd490b0
1 changed files with 38 additions and 15 deletions
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53
sched.c
View file

@ -539,28 +539,49 @@ handle_slew(struct timeval *raw,
#define JUMP_DETECT_THRESHOLD 10 #define JUMP_DETECT_THRESHOLD 10
static int static int
check_current_time(struct timeval *raw, int timeout) check_current_time(struct timeval *prev_raw, struct timeval *raw, int timeout,
struct timeval *orig_select_tv,
struct timeval *rem_select_tv)
{ {
double diff; struct timeval elapsed_min, elapsed_max;
double step, elapsed;
if (last_select_ts_raw.tv_sec > raw->tv_sec + JUMP_DETECT_THRESHOLD) { /* Get an estimate of the time spent waiting in the select() call. On some
systems (e.g. Linux) the timeout timeval is modified to return the
remaining time, use that information. */
if (timeout) {
elapsed_max = elapsed_min = *orig_select_tv;
} else if (rem_select_tv && rem_select_tv->tv_sec >= 0 &&
rem_select_tv->tv_sec <= orig_select_tv->tv_sec &&
(rem_select_tv->tv_sec != orig_select_tv->tv_sec ||
rem_select_tv->tv_usec != orig_select_tv->tv_usec)) {
UTI_DiffTimevals(&elapsed_min, orig_select_tv, rem_select_tv);
elapsed_max = elapsed_min;
} else {
if (rem_select_tv)
elapsed_max = *orig_select_tv;
else
UTI_DiffTimevals(&elapsed_max, raw, prev_raw);
elapsed_min.tv_sec = 0;
elapsed_min.tv_usec = 0;
}
if (last_select_ts_raw.tv_sec + elapsed_min.tv_sec >
raw->tv_sec + JUMP_DETECT_THRESHOLD) {
LOG(LOGS_WARN, LOGF_Scheduler, "Backward time jump detected!"); LOG(LOGS_WARN, LOGF_Scheduler, "Backward time jump detected!");
} else if (n_timer_queue_entries > 0 && } else if (prev_raw->tv_sec + elapsed_max.tv_sec + JUMP_DETECT_THRESHOLD <
timer_queue.next->tv.tv_sec + JUMP_DETECT_THRESHOLD < raw->tv_sec) { raw->tv_sec) {
LOG(LOGS_WARN, LOGF_Scheduler, "Forward time jump detected!"); LOG(LOGS_WARN, LOGF_Scheduler, "Forward time jump detected!");
} else { } else {
return 1; return 1;
} }
if (timeout) { UTI_DiffTimevalsToDouble(&step, &last_select_ts_raw, raw);
assert(n_timer_queue_entries > 0); UTI_TimevalToDouble(&elapsed_min, &elapsed);
UTI_DiffTimevalsToDouble(&diff, &timer_queue.next->tv, raw); step += elapsed;
} else {
UTI_DiffTimevalsToDouble(&diff, &last_select_ts_raw, raw);
}
/* Cooked time may no longer be valid after dispatching the handlers */ /* Cooked time may no longer be valid after dispatching the handlers */
LCL_NotifyExternalTimeStep(raw, raw, diff, fabs(diff)); LCL_NotifyExternalTimeStep(raw, raw, step, fabs(step));
return 0; return 0;
} }
@ -572,8 +593,8 @@ SCH_MainLoop(void)
{ {
fd_set rd; fd_set rd;
int status, errsv; int status, errsv;
struct timeval tv, *ptv; struct timeval tv, saved_tv, *ptv;
struct timeval now, cooked; struct timeval now, saved_now, cooked;
double err; double err;
assert(initialised); assert(initialised);
@ -581,6 +602,7 @@ SCH_MainLoop(void)
while (!need_to_exit) { while (!need_to_exit) {
/* Dispatch timeouts and fill now with current raw time */ /* Dispatch timeouts and fill now with current raw time */
dispatch_timeouts(&now); dispatch_timeouts(&now);
saved_now = now;
/* The timeout handlers may request quit */ /* The timeout handlers may request quit */
if (need_to_exit) if (need_to_exit)
@ -592,6 +614,7 @@ SCH_MainLoop(void)
UTI_DiffTimevals(&tv, &(timer_queue.next->tv), &now); UTI_DiffTimevals(&tv, &(timer_queue.next->tv), &now);
ptv = &tv; ptv = &tv;
assert(tv.tv_sec > 0 || tv.tv_usec > 0); assert(tv.tv_sec > 0 || tv.tv_usec > 0);
saved_tv = tv;
} else { } else {
ptv = NULL; ptv = NULL;
@ -613,7 +636,7 @@ SCH_MainLoop(void)
LCL_CookTime(&now, &cooked, &err); LCL_CookTime(&now, &cooked, &err);
/* Check if the time didn't jump unexpectedly */ /* Check if the time didn't jump unexpectedly */
if (!check_current_time(&now, status == 0)) { if (!check_current_time(&saved_now, &now, status == 0, &saved_tv, ptv)) {
/* Cook the time again after handling the step */ /* Cook the time again after handling the step */
LCL_CookTime(&now, &cooked, &err); LCL_CookTime(&now, &cooked, &err);
} }