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core/timer: Introduce RandomOffsetSec= knob (#36437)

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This is like RandomDelaySec, but it doesn't reset whenever the manager
restarts.

Fixes https://github.com/systemd/systemd/issues/21166
This commit is contained in:
Lennart Poettering
2025-06-17 16:05:12 +02:00
committed by GitHub
parent ef3a0ed834 9a0749c82b
commit 279962a9e8
7 changed files with 75 additions and 23 deletions
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src/core/timer.c
+18 -9
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@@ -348,18 +348,18 @@ static void timer_enter_elapsed(Timer *t, bool leave_around) {
timer_enter_dead(t, TIMER_SUCCESS);
}
static void add_random(Timer *t, usec_t *v) {
static void add_random_delay(Timer *t, usec_t *v) {
usec_t add;
assert(t);
assert(v);
if (t->random_usec == 0)
if (t->random_delay_usec == 0)
return;
if (*v == USEC_INFINITY)
return;
add = (t->fixed_random_delay ? timer_get_fixed_delay_hash(t) : random_u64()) % t->random_usec;
add = (t->fixed_random_delay ? timer_get_fixed_delay_hash(t) : random_u64()) % t->random_delay_usec;
if (*v + add < *v) /* overflow */
*v = (usec_t) -2; /* Highest possible value, that is not USEC_INFINITY */
@@ -392,12 +392,19 @@ static void timer_enter_waiting(Timer *t, bool time_change) {
continue;
if (v->base == TIMER_CALENDAR) {
usec_t b, rebased;
usec_t b, rebased, random_offset = 0;
if (t->random_offset_usec != 0)
random_offset = timer_get_fixed_delay_hash(t) % t->random_offset_usec;
/* If DeferReactivation= is enabled, schedule the job based on the last time
* the trigger unit entered inactivity. Otherwise, if we know the last time
* this was triggered, schedule the job based relative to that. If we don't,
* just start from the activation time or realtime. */
* just start from the activation time or realtime.
*
* Unless we have a real last-trigger time, we subtract the random_offset because
* any event that elapsed within the last random_offset has actually been delayed
* and thus hasn't truly elapsed yet. */
if (t->defer_reactivation &&
dual_timestamp_is_set(&trigger->inactive_enter_timestamp)) {
@@ -409,14 +416,16 @@ static void timer_enter_waiting(Timer *t, bool time_change) {
} else if (dual_timestamp_is_set(&t->last_trigger))
b = t->last_trigger.realtime;
else if (dual_timestamp_is_set(&UNIT(t)->inactive_exit_timestamp))
b = UNIT(t)->inactive_exit_timestamp.realtime;
b = UNIT(t)->inactive_exit_timestamp.realtime - random_offset;
else
b = ts.realtime;
b = ts.realtime - random_offset;
r = calendar_spec_next_usec(v->calendar_spec, b, &v->next_elapse);
if (r < 0)
continue;
v->next_elapse += random_offset;
/* To make the delay due to RandomizedDelaySec= work even at boot, if the scheduled
* time has already passed, set the time when systemd first started as the scheduled
* time. Note that we base this on the monotonic timestamp of the boot, not the
@@ -506,7 +515,7 @@ static void timer_enter_waiting(Timer *t, bool time_change) {
if (found_monotonic) {
usec_t left;
add_random(t, &t->next_elapse_monotonic_or_boottime);
add_random_delay(t, &t->next_elapse_monotonic_or_boottime);
left = usec_sub_unsigned(t->next_elapse_monotonic_or_boottime, triple_timestamp_by_clock(&ts, TIMER_MONOTONIC_CLOCK(t)));
log_unit_debug(UNIT(t), "Monotonic timer elapses in %s.", FORMAT_TIMESPAN(left, 0));
@@ -547,7 +556,7 @@ static void timer_enter_waiting(Timer *t, bool time_change) {
}
if (found_realtime) {
add_random(t, &t->next_elapse_realtime);
add_random_delay(t, &t->next_elapse_realtime);
log_unit_debug(UNIT(t), "Realtime timer elapses at %s.", FORMAT_TIMESTAMP(t->next_elapse_realtime));