From 338b8f9bca1cd7bd65123808fc7f7b2773e637db Mon Sep 17 00:00:00 2001

From: Lennart Poettering <lennart@poettering.net>

Date: Wed, 18 Nov 2015 13:37:30 +0100

Subject: [PATCH] core: add new RandomSec= setting for time units

This allows configuration of a random time on top of the elapse events,

in order to spread time events in a network evenly across a range.

Cherry-picked from: 744c7693751830149ae78fdaf95c6c6f99d59f07

Resolves: #1305279

---

 man/systemd.timer.xml                 | 43 ++++++++++++++++++++++++++++++-----

 src/core/dbus-timer.c                 | 17 ++++++++++++++

 src/core/load-fragment-gperf.gperf.m4 |  1 +

 src/core/timer.c                      | 28 +++++++++++++++++++++++

 src/core/timer.h                      |  1 +

 src/libsystemd/sd-bus/bus-util.c      | 16 +++++++++++++

 6 files changed, 100 insertions(+), 6 deletions(-)

diff --git a/man/systemd.timer.xml b/man/systemd.timer.xml

index 20890f2..bdd14d8 100644

--- a/man/systemd.timer.xml

+++ b/man/systemd.timer.xml

@@ -180,13 +180,12 @@

         <varname>OnUnitInactiveSec=</varname> and ending the time

         configured with <varname>AccuracySec=</varname> later. Within

         this time window, the expiry time will be placed at a

-        host-specific, randomized but stable position that is

+        host-specific, randomized, but stable position that is

         synchronized between all local timer units. This is done in

-        order to distribute the wake-up time in networked

-        installations, as well as optimizing power consumption to

-        suppress unnecessary CPU wake-ups. To get best accuracy, set

-        this option to 1us. Note that the timer is still subject to

-        the timer slack configured via

+        order to optimize power consumption to suppress unnecessary

+        CPU wake-ups. To get best accuracy, set this option to

+        1us. Note that the timer is still subject to the timer slack

+        configured via

         <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>'s

         <varname>TimerSlackNSec=</varname> setting. See

         <citerefentry><refentrytitle>prctl</refentrytitle><manvolnum>2</manvolnum></citerefentry>

@@ -194,6 +193,38 @@

         this value as high as possible and as low as

         necessary.</para></listitem>

       </varlistentry>

+

+      <varlistentry>

+        <term><varname>RandomSec=</varname></term>

+

+        <listitem><para>Delay the timer by a randomly selected, evenly

+        distributed amount of time between 0 and the specified time

+        value. Defaults to 0, indicating that no randomized delay

+        shall be applied. Each timer unit will determine this delay

+        randomly each time it is started, and the delay will simply be

+        added on top of the next determined elapsing time. This is

+        useful to stretch dispatching of similarly configured timer

+        events over a certain amount time, to avoid that they all fire

+        at the same time, possibly resulting in resource

+        congestion. Note the relation to

+        <varname>AccuracySec=</varname> above: the latter allows the

+        service manager to coalesce timer events within a specified

+        time range in order to minimize wakeups, the former does the

+        opposite: it stretches timer events over a time range, to make

+        it unlikely that they fire simultaneously. If

+        <varname>RandomSec=</varname> and

+        <varname>AccuracySec=</varname> are used in conjunction, first

+        the a randomized time is added, and the result is then

+        possibly shifted further to coalesce it with other timer

+        events possibly happening on the system. As mentioned above

+        <varname>AccuracySec=</varname> defaults to 1min and

+        <varname>RandomSec=</varname> to 0, thus encouraging

+        coalescing of timer events. In order to optimally stretch

+        timer events over a certain range of time, make sure to set

+        <varname>RandomSec=</varname> to a higher value, and

+        <varname>AccuracySec=1us</varname>.</para></listitem>

+      </varlistentry>

+

       <varlistentry>

         <term><varname>Unit=</varname></term>

diff --git a/src/core/dbus-timer.c b/src/core/dbus-timer.c

index 43e7852..cd7bf44 100644

--- a/src/core/dbus-timer.c

+++ b/src/core/dbus-timer.c

@@ -181,6 +181,7 @@ const sd_bus_vtable bus_timer_vtable[] = {

         BUS_PROPERTY_DUAL_TIMESTAMP("LastTriggerUSec", offsetof(Timer, last_trigger), SD_BUS_VTABLE_PROPERTY_EMITS_CHANGE),

         SD_BUS_PROPERTY("Result", "s", property_get_result, offsetof(Timer, result), SD_BUS_VTABLE_PROPERTY_EMITS_CHANGE),

         SD_BUS_PROPERTY("AccuracyUSec", "t", bus_property_get_usec, offsetof(Timer, accuracy_usec), SD_BUS_VTABLE_PROPERTY_CONST),

+        SD_BUS_PROPERTY("RandomUSec", "t", bus_property_get_usec, offsetof(Timer, random_usec), SD_BUS_VTABLE_PROPERTY_CONST),

         SD_BUS_PROPERTY("Persistent", "b", bus_property_get_bool, offsetof(Timer, persistent), SD_BUS_VTABLE_PROPERTY_CONST),

         SD_BUS_PROPERTY("WakeSystem", "b", bus_property_get_bool, offsetof(Timer, wake_system), SD_BUS_VTABLE_PROPERTY_CONST),

         SD_BUS_VTABLE_END

@@ -284,6 +285,22 @@ static int bus_timer_set_transient_property(

                 return 1;

+        } else if (streq(name, "RandomUSec")) {

+                usec_t u = 0;

+

+                r = sd_bus_message_read(message, "t", &u);

+                if (r < 0)

+                        return r;

+

+                if (mode != UNIT_CHECK) {

+                        char time[FORMAT_TIMESPAN_MAX];

+

+                        t->random_usec = u;

+                        unit_write_drop_in_private_format(UNIT(t), mode, name, "RandomSec=%s\n", format_timespan(time, sizeof(time), u, USEC_PER_MSEC));

+                }

+

+                return 1;

+

         } else if (streq(name, "WakeSystem")) {

                 int b;

diff --git a/src/core/load-fragment-gperf.gperf.m4 b/src/core/load-fragment-gperf.gperf.m4

index 5305984..5106a98 100644

--- a/src/core/load-fragment-gperf.gperf.m4

+++ b/src/core/load-fragment-gperf.gperf.m4

@@ -336,6 +336,7 @@ Timer.OnUnitInactiveSec,         config_parse_timer,                 0,

 Timer.Persistent,                config_parse_bool,                  0,                             offsetof(Timer, persistent)

 Timer.WakeSystem,                config_parse_bool,                  0,                             offsetof(Timer, wake_system)

 Timer.AccuracySec,               config_parse_sec,                   0,                             offsetof(Timer, accuracy_usec)

+Timer.RandomSec,                 config_parse_sec,                   0,                             offsetof(Timer, random_usec)

 Timer.Unit,                      config_parse_trigger_unit,          0,                             0

 m4_dnl

 Path.PathExists,                 config_parse_path_spec,             0,                             0

diff --git a/src/core/timer.c b/src/core/timer.c

index 48cf9c1..972dd73 100644

--- a/src/core/timer.c

+++ b/src/core/timer.c

@@ -29,6 +29,7 @@

 #include "bus-util.h"

 #include "bus-error.h"

 #include "mkdir.h"

+#include "util.h"

 static const UnitActiveState state_translation_table[_TIMER_STATE_MAX] = {

         [TIMER_DEAD] = UNIT_INACTIVE,

@@ -315,6 +316,28 @@ static usec_t monotonic_to_boottime(usec_t t) {

                 return 0;

 }

+static void add_random(Timer *t, usec_t *v) {

+        char s[FORMAT_TIMESPAN_MAX];

+        usec_t add;

+

+        assert(t);

+        assert(*v);

+

+        if (t->random_usec == 0)

+                return;

+        if (*v == USEC_INFINITY)

+                return;

+

+        add = random_u64() % t->random_usec;

+

+        if (*v + add < *v) /* overflow */

+                *v = (usec_t) -2; /* Highest possible value, that is not USEC_INFINITY */

+        else

+                *v += add;

+

+        log_unit_info(UNIT(t)->id, "Adding %s random time.", format_timespan(s, sizeof(s), add, 0));

+}

+

 static void timer_enter_waiting(Timer *t, bool initial) {

         bool found_monotonic = false, found_realtime = false;

         usec_t ts_realtime, ts_monotonic;

@@ -431,6 +454,8 @@ static void timer_enter_waiting(Timer *t, bool initial) {

         if (found_monotonic) {

                 char buf[FORMAT_TIMESPAN_MAX];

+                add_random(t, &t->next_elapse_monotonic_or_boottime);

+

                 log_unit_debug(UNIT(t)->id, "%s: Monotonic timer elapses in %s.",

                                UNIT(t)->id,

                                format_timespan(buf, sizeof(buf), t->next_elapse_monotonic_or_boottime > ts_monotonic ? t->next_elapse_monotonic_or_boottime - ts_monotonic : 0, 0));

@@ -460,6 +485,9 @@ static void timer_enter_waiting(Timer *t, bool initial) {

         if (found_realtime) {

                 char buf[FORMAT_TIMESTAMP_MAX];

+

+                add_random(t, &t->next_elapse_realtime);

+

                 log_unit_debug(UNIT(t)->id, "%s: Realtime timer elapses at %s.", UNIT(t)->id, format_timestamp(buf, sizeof(buf), t->next_elapse_realtime));

                 if (t->realtime_event_source) {

diff --git a/src/core/timer.h b/src/core/timer.h

index de412a0..b977245 100644

--- a/src/core/timer.h

+++ b/src/core/timer.h

@@ -69,6 +69,7 @@ struct Timer {

         Unit meta;

         usec_t accuracy_usec;

+        usec_t random_usec;

         LIST_HEAD(TimerValue, values);

         usec_t next_elapse_realtime;

diff --git a/src/libsystemd/sd-bus/bus-util.c b/src/libsystemd/sd-bus/bus-util.c

index 6d56150..5ecb3be 100644

--- a/src/libsystemd/sd-bus/bus-util.c

+++ b/src/libsystemd/sd-bus/bus-util.c

@@ -1364,6 +1364,22 @@ int bus_append_unit_property_assignment(sd_bus_message *m, const char *assignmen

                         return bus_log_create_error(r);

                 return 0;

+        } else if (streq(field, "RandomSec")) {

+                usec_t t;

+

+                r = parse_sec(eq, &t);

+                if (r < 0)

+                        return log_error_errno(r, "Failed to parse RandomSec= parameter: %s", eq);

+

+                r = sd_bus_message_append_basic(m, SD_BUS_TYPE_STRING, "RandomUSec");

+                if (r < 0)

+                        return bus_log_create_error(r);

+

+                r = sd_bus_message_append(m, "v", "t", t);

+                if (r < 0)

+                        return bus_log_create_error(r);

+

+                return 0;

         }

         r = sd_bus_message_append_basic(m, SD_BUS_TYPE_STRING, field);