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228 lines
10 KiB
228 lines
10 KiB
7 years ago
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From 338b8f9bca1cd7bd65123808fc7f7b2773e637db Mon Sep 17 00:00:00 2001
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From: Lennart Poettering <lennart@poettering.net>
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Date: Wed, 18 Nov 2015 13:37:30 +0100
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Subject: [PATCH] core: add new RandomSec= setting for time units
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This allows configuration of a random time on top of the elapse events,
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in order to spread time events in a network evenly across a range.
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Cherry-picked from: 744c7693751830149ae78fdaf95c6c6f99d59f07
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Resolves: #1305279
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---
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man/systemd.timer.xml | 43 ++++++++++++++++++++++++++++++-----
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src/core/dbus-timer.c | 17 ++++++++++++++
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src/core/load-fragment-gperf.gperf.m4 | 1 +
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src/core/timer.c | 28 +++++++++++++++++++++++
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src/core/timer.h | 1 +
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src/libsystemd/sd-bus/bus-util.c | 16 +++++++++++++
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6 files changed, 100 insertions(+), 6 deletions(-)
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diff --git a/man/systemd.timer.xml b/man/systemd.timer.xml
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index 20890f227..bdd14d888 100644
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--- a/man/systemd.timer.xml
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+++ b/man/systemd.timer.xml
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@@ -180,13 +180,12 @@
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<varname>OnUnitInactiveSec=</varname> and ending the time
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configured with <varname>AccuracySec=</varname> later. Within
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this time window, the expiry time will be placed at a
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- host-specific, randomized but stable position that is
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+ host-specific, randomized, but stable position that is
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synchronized between all local timer units. This is done in
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- order to distribute the wake-up time in networked
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- installations, as well as optimizing power consumption to
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- suppress unnecessary CPU wake-ups. To get best accuracy, set
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- this option to 1us. Note that the timer is still subject to
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- the timer slack configured via
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+ order to optimize power consumption to suppress unnecessary
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+ CPU wake-ups. To get best accuracy, set this option to
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+ 1us. Note that the timer is still subject to the timer slack
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+ configured via
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<citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>'s
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<varname>TimerSlackNSec=</varname> setting. See
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<citerefentry><refentrytitle>prctl</refentrytitle><manvolnum>2</manvolnum></citerefentry>
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@@ -194,6 +193,38 @@
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this value as high as possible and as low as
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necessary.</para></listitem>
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</varlistentry>
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+
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+ <varlistentry>
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+ <term><varname>RandomSec=</varname></term>
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+
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+ <listitem><para>Delay the timer by a randomly selected, evenly
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+ distributed amount of time between 0 and the specified time
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+ value. Defaults to 0, indicating that no randomized delay
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+ shall be applied. Each timer unit will determine this delay
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+ randomly each time it is started, and the delay will simply be
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+ added on top of the next determined elapsing time. This is
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+ useful to stretch dispatching of similarly configured timer
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+ events over a certain amount time, to avoid that they all fire
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+ at the same time, possibly resulting in resource
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+ congestion. Note the relation to
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+ <varname>AccuracySec=</varname> above: the latter allows the
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+ service manager to coalesce timer events within a specified
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+ time range in order to minimize wakeups, the former does the
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+ opposite: it stretches timer events over a time range, to make
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+ it unlikely that they fire simultaneously. If
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+ <varname>RandomSec=</varname> and
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+ <varname>AccuracySec=</varname> are used in conjunction, first
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+ the a randomized time is added, and the result is then
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+ possibly shifted further to coalesce it with other timer
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+ events possibly happening on the system. As mentioned above
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+ <varname>AccuracySec=</varname> defaults to 1min and
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+ <varname>RandomSec=</varname> to 0, thus encouraging
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+ coalescing of timer events. In order to optimally stretch
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+ timer events over a certain range of time, make sure to set
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+ <varname>RandomSec=</varname> to a higher value, and
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+ <varname>AccuracySec=1us</varname>.</para></listitem>
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+ </varlistentry>
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+
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<varlistentry>
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<term><varname>Unit=</varname></term>
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diff --git a/src/core/dbus-timer.c b/src/core/dbus-timer.c
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index 43e785246..cd7bf44ba 100644
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--- a/src/core/dbus-timer.c
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+++ b/src/core/dbus-timer.c
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@@ -181,6 +181,7 @@ const sd_bus_vtable bus_timer_vtable[] = {
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BUS_PROPERTY_DUAL_TIMESTAMP("LastTriggerUSec", offsetof(Timer, last_trigger), SD_BUS_VTABLE_PROPERTY_EMITS_CHANGE),
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SD_BUS_PROPERTY("Result", "s", property_get_result, offsetof(Timer, result), SD_BUS_VTABLE_PROPERTY_EMITS_CHANGE),
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SD_BUS_PROPERTY("AccuracyUSec", "t", bus_property_get_usec, offsetof(Timer, accuracy_usec), SD_BUS_VTABLE_PROPERTY_CONST),
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+ SD_BUS_PROPERTY("RandomUSec", "t", bus_property_get_usec, offsetof(Timer, random_usec), SD_BUS_VTABLE_PROPERTY_CONST),
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SD_BUS_PROPERTY("Persistent", "b", bus_property_get_bool, offsetof(Timer, persistent), SD_BUS_VTABLE_PROPERTY_CONST),
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SD_BUS_PROPERTY("WakeSystem", "b", bus_property_get_bool, offsetof(Timer, wake_system), SD_BUS_VTABLE_PROPERTY_CONST),
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SD_BUS_VTABLE_END
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@@ -284,6 +285,22 @@ static int bus_timer_set_transient_property(
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return 1;
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+ } else if (streq(name, "RandomUSec")) {
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+ usec_t u = 0;
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+
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+ r = sd_bus_message_read(message, "t", &u);
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+ if (r < 0)
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+ return r;
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+
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+ if (mode != UNIT_CHECK) {
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+ char time[FORMAT_TIMESPAN_MAX];
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+
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+ t->random_usec = u;
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+ unit_write_drop_in_private_format(UNIT(t), mode, name, "RandomSec=%s\n", format_timespan(time, sizeof(time), u, USEC_PER_MSEC));
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+ }
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+
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+ return 1;
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+
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} else if (streq(name, "WakeSystem")) {
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int b;
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diff --git a/src/core/load-fragment-gperf.gperf.m4 b/src/core/load-fragment-gperf.gperf.m4
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index 53059845e..5106a98ee 100644
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--- a/src/core/load-fragment-gperf.gperf.m4
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+++ b/src/core/load-fragment-gperf.gperf.m4
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@@ -336,6 +336,7 @@ Timer.OnUnitInactiveSec, config_parse_timer, 0,
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Timer.Persistent, config_parse_bool, 0, offsetof(Timer, persistent)
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Timer.WakeSystem, config_parse_bool, 0, offsetof(Timer, wake_system)
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Timer.AccuracySec, config_parse_sec, 0, offsetof(Timer, accuracy_usec)
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+Timer.RandomSec, config_parse_sec, 0, offsetof(Timer, random_usec)
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Timer.Unit, config_parse_trigger_unit, 0, 0
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m4_dnl
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Path.PathExists, config_parse_path_spec, 0, 0
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diff --git a/src/core/timer.c b/src/core/timer.c
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index 48cf9c16a..972dd73df 100644
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--- a/src/core/timer.c
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+++ b/src/core/timer.c
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@@ -29,6 +29,7 @@
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#include "bus-util.h"
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#include "bus-error.h"
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#include "mkdir.h"
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+#include "util.h"
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static const UnitActiveState state_translation_table[_TIMER_STATE_MAX] = {
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[TIMER_DEAD] = UNIT_INACTIVE,
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@@ -315,6 +316,28 @@ static usec_t monotonic_to_boottime(usec_t t) {
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return 0;
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}
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+static void add_random(Timer *t, usec_t *v) {
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+ char s[FORMAT_TIMESPAN_MAX];
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+ usec_t add;
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+
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+ assert(t);
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+ assert(*v);
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+
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+ if (t->random_usec == 0)
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+ return;
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+ if (*v == USEC_INFINITY)
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+ return;
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+
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+ add = random_u64() % t->random_usec;
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+
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+ if (*v + add < *v) /* overflow */
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+ *v = (usec_t) -2; /* Highest possible value, that is not USEC_INFINITY */
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+ else
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+ *v += add;
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+
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+ log_unit_info(UNIT(t)->id, "Adding %s random time.", format_timespan(s, sizeof(s), add, 0));
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+}
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+
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static void timer_enter_waiting(Timer *t, bool initial) {
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bool found_monotonic = false, found_realtime = false;
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usec_t ts_realtime, ts_monotonic;
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@@ -431,6 +454,8 @@ static void timer_enter_waiting(Timer *t, bool initial) {
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if (found_monotonic) {
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char buf[FORMAT_TIMESPAN_MAX];
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+ add_random(t, &t->next_elapse_monotonic_or_boottime);
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+
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log_unit_debug(UNIT(t)->id, "%s: Monotonic timer elapses in %s.",
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UNIT(t)->id,
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format_timespan(buf, sizeof(buf), t->next_elapse_monotonic_or_boottime > ts_monotonic ? t->next_elapse_monotonic_or_boottime - ts_monotonic : 0, 0));
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@@ -460,6 +485,9 @@ static void timer_enter_waiting(Timer *t, bool initial) {
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if (found_realtime) {
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char buf[FORMAT_TIMESTAMP_MAX];
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+
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+ add_random(t, &t->next_elapse_realtime);
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+
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log_unit_debug(UNIT(t)->id, "%s: Realtime timer elapses at %s.", UNIT(t)->id, format_timestamp(buf, sizeof(buf), t->next_elapse_realtime));
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if (t->realtime_event_source) {
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diff --git a/src/core/timer.h b/src/core/timer.h
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index de412a043..b97724525 100644
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--- a/src/core/timer.h
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+++ b/src/core/timer.h
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@@ -69,6 +69,7 @@ struct Timer {
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Unit meta;
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usec_t accuracy_usec;
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+ usec_t random_usec;
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LIST_HEAD(TimerValue, values);
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usec_t next_elapse_realtime;
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diff --git a/src/libsystemd/sd-bus/bus-util.c b/src/libsystemd/sd-bus/bus-util.c
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index 6d5615082..5ecb3bea4 100644
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--- a/src/libsystemd/sd-bus/bus-util.c
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+++ b/src/libsystemd/sd-bus/bus-util.c
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@@ -1360,6 +1360,22 @@ int bus_append_unit_property_assignment(sd_bus_message *m, const char *assignmen
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return -EINVAL;
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}
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+ if (r < 0)
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+ return bus_log_create_error(r);
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+
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+ return 0;
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+ } else if (streq(field, "RandomSec")) {
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+ usec_t t;
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+
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+ r = parse_sec(eq, &t);
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+ if (r < 0)
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+ return log_error_errno(r, "Failed to parse RandomSec= parameter: %s", eq);
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+
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+ r = sd_bus_message_append_basic(m, SD_BUS_TYPE_STRING, "RandomUSec");
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+ if (r < 0)
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+ return bus_log_create_error(r);
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+
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+ r = sd_bus_message_append(m, "v", "t", t);
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if (r < 0)
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return bus_log_create_error(r);
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