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systemd/1365-core-make-manager-event-loop-rate-limit-configurable.patch
Jan Macku 00712f2c9c systemd-252-76 
Resolves: RHEL-208860, RHEL-137251, RHEL-118224, RHEL-213655, RHEL-212610
2026-08-05 09:38:59 +02:00

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From 9d258e84de4235fe807990782752f8b9d8e54c59 Mon Sep 17 00:00:00 2001
From: Michal Sekletar <msekleta@redhat.com>
Date: Wed, 13 May 2026 16:20:55 +0200
Subject: [PATCH] core: make manager event loop rate limit configurable
Co-developed-by: Claude Opus 4.6 <noreply@anthropic.com>
(cherry picked from commit e1c63fd4c0657a7fc7b749c64283ab4dbc6fb39e)
Resolves: RHEL-213655
---
man/org.freedesktop.systemd1.xml | 12 ++++++++++++
man/systemd-system.conf.xml | 15 +++++++++++++++
src/core/dbus-manager.c | 2 ++
src/core/main.c | 31 +++++++++++++++++++++++++++++++
src/core/manager-serialize.c | 4 ++++
src/core/manager.c | 3 +--
src/core/manager.h | 3 +++
src/core/system.conf.in | 2 ++
src/core/user.conf.in | 2 ++
9 files changed, 72 insertions(+), 2 deletions(-)
diff --git a/man/org.freedesktop.systemd1.xml b/man/org.freedesktop.systemd1.xml
index 8298b726b7..51e017bf10 100644
--- a/man/org.freedesktop.systemd1.xml
+++ b/man/org.freedesktop.systemd1.xml
@@ -524,6 +524,10 @@ node /org/freedesktop/systemd1 {
@org.freedesktop.DBus.Property.EmitsChangedSignal("false")
readonly t DefaultTasksMax = ...;
@org.freedesktop.DBus.Property.EmitsChangedSignal("const")
+ readonly t EventLoopRateLimitIntervalUSec = ...;
+ @org.freedesktop.DBus.Property.EmitsChangedSignal("const")
+ readonly u EventLoopRateLimitBurst = ...;
+ @org.freedesktop.DBus.Property.EmitsChangedSignal("const")
readonly t TimerSlackNSec = ...;
@org.freedesktop.DBus.Property.EmitsChangedSignal("const")
readonly s DefaultOOMPolicy = '...';
@@ -776,6 +780,10 @@ node /org/freedesktop/systemd1 {
<!--property DefaultTasksMax is not documented!-->
+ <!--property EventLoopRateLimitIntervalUSec is not documented!-->
+
+ <!--property EventLoopRateLimitBurst is not documented!-->
+
<!--property TimerSlackNSec is not documented!-->
<!--property DefaultOOMPolicy is not documented!-->
@@ -1200,6 +1208,10 @@ node /org/freedesktop/systemd1 {
<variablelist class="dbus-property" generated="True" extra-ref="DefaultTasksMax"/>
+ <variablelist class="dbus-property" generated="True" extra-ref="EventLoopRateLimitIntervalUSec"/>
+
+ <variablelist class="dbus-property" generated="True" extra-ref="EventLoopRateLimitBurst"/>
+
<variablelist class="dbus-property" generated="True" extra-ref="TimerSlackNSec"/>
<variablelist class="dbus-property" generated="True" extra-ref="DefaultOOMPolicy"/>
diff --git a/man/systemd-system.conf.xml b/man/systemd-system.conf.xml
index 00de04d426..e563be8615 100644
--- a/man/systemd-system.conf.xml
+++ b/man/systemd-system.conf.xml
@@ -550,6 +550,21 @@
<para>If the value is <literal>/</literal>, only labels specified with <varname>SmackProcessLabel=</varname>
are assigned and the compile-time default is ignored.</para></listitem>
</varlistentry>
+
+ <varlistentry>
+ <term><varname>EventLoopRateLimitIntervalSec=</varname></term>
+ <term><varname>EventLoopRateLimitBurst=</varname></term>
+
+ <listitem><para>Configures the rate limiting applied to the manager's main event loop. If the event
+ loop iterates more than <varname>EventLoopRateLimitBurst=</varname> times within
+ <varname>EventLoopRateLimitIntervalSec=</varname>, event processing is briefly paused to prevent
+ excessive CPU usage. <varname>EventLoopRateLimitIntervalSec=</varname> defaults to 1s.
+ <varname>EventLoopRateLimitBurst=</varname> defaults to 50000. These settings can also be set on the
+ kernel command line via
+ <varname>systemd.event_loop_ratelimit_interval_sec=</varname> and
+ <varname>systemd.event_loop_ratelimit_burst=</varname>.</para></listitem>
+ </varlistentry>
+
</variablelist>
</refsect1>
diff --git a/src/core/dbus-manager.c b/src/core/dbus-manager.c
index 16c9680d80..2537c4adf8 100644
--- a/src/core/dbus-manager.c
+++ b/src/core/dbus-manager.c
@@ -2911,6 +2911,8 @@ const sd_bus_vtable bus_manager_vtable[] = {
SD_BUS_PROPERTY("DefaultLimitRTTIME", "t", bus_property_get_rlimit, offsetof(Manager, rlimit[RLIMIT_RTTIME]), SD_BUS_VTABLE_PROPERTY_CONST),
SD_BUS_PROPERTY("DefaultLimitRTTIMESoft", "t", bus_property_get_rlimit, offsetof(Manager, rlimit[RLIMIT_RTTIME]), SD_BUS_VTABLE_PROPERTY_CONST),
SD_BUS_PROPERTY("DefaultTasksMax", "t", bus_property_get_tasks_max, offsetof(Manager, default_tasks_max), 0),
+ SD_BUS_PROPERTY("EventLoopRateLimitIntervalUSec", "t", bus_property_get_usec, offsetof(Manager, event_loop_ratelimit.interval), SD_BUS_VTABLE_PROPERTY_CONST),
+ SD_BUS_PROPERTY("EventLoopRateLimitBurst", "u", bus_property_get_unsigned, offsetof(Manager, event_loop_ratelimit.burst), SD_BUS_VTABLE_PROPERTY_CONST),
SD_BUS_PROPERTY("TimerSlackNSec", "t", property_get_timer_slack_nsec, 0, SD_BUS_VTABLE_PROPERTY_CONST),
SD_BUS_PROPERTY("DefaultOOMPolicy", "s", bus_property_get_oom_policy, offsetof(Manager, default_oom_policy), SD_BUS_VTABLE_PROPERTY_CONST),
SD_BUS_PROPERTY("DefaultOOMScoreAdjust", "i", property_get_oom_score_adjust, 0, SD_BUS_VTABLE_PROPERTY_CONST),
diff --git a/src/core/main.c b/src/core/main.c
index 18f5781126..1e45ed6bd6 100644
--- a/src/core/main.c
+++ b/src/core/main.c
@@ -173,6 +173,8 @@ static size_t arg_random_seed_size;
static int arg_default_oom_score_adjust;
static bool arg_default_oom_score_adjust_set;
static char *arg_default_smack_process_label;
+static usec_t arg_event_loop_ratelimit_interval_sec;
+static unsigned arg_event_loop_ratelimit_burst;
/* A copy of the original environment block */
static char **saved_env = NULL;
@@ -483,6 +485,28 @@ static int parse_proc_cmdline_item(const char *key, const char *value, void *dat
arg_random_seed = sz > 0 ? p : mfree(p);
arg_random_seed_size = sz;
+ } else if (proc_cmdline_key_streq(key, "systemd.event_loop_ratelimit_interval_sec")) {
+
+ if (proc_cmdline_value_missing(key, value))
+ return 0;
+
+ r = parse_sec(value, &arg_event_loop_ratelimit_interval_sec);
+ if (r < 0) {
+ log_warning_errno(r, "Failed to parse systemd.event_loop_ratelimit_interval_sec= argument '%s', ignoring: %m", value);
+ return 0;
+ }
+
+ } else if (proc_cmdline_key_streq(key, "systemd.event_loop_ratelimit_burst")) {
+
+ if (proc_cmdline_value_missing(key, value))
+ return 0;
+
+ r = safe_atou(value, &arg_event_loop_ratelimit_burst);
+ if (r < 0) {
+ log_warning_errno(r, "Failed to parse systemd.event_loop_ratelimit_burst= argument '%s', ignoring: %m", value);
+ return 0;
+ }
+
} else if (streq(key, "quiet") && !value) {
if (arg_show_status == _SHOW_STATUS_INVALID)
@@ -662,6 +686,8 @@ static int parse_config_file(void) {
{ "Manager", "CtrlAltDelBurstAction", config_parse_emergency_action, arg_runtime_scope, &arg_cad_burst_action },
{ "Manager", "DefaultOOMPolicy", config_parse_oom_policy, 0, &arg_default_oom_policy },
{ "Manager", "DefaultOOMScoreAdjust", config_parse_oom_score_adjust, 0, NULL },
+ { "Manager", "EventLoopRateLimitIntervalSec", config_parse_sec, 0, &arg_event_loop_ratelimit_interval_sec },
+ { "Manager", "EventLoopRateLimitBurst", config_parse_unsigned, 0, &arg_event_loop_ratelimit_burst },
#if ENABLE_SMACK
{ "Manager", "DefaultSmackProcessLabel", config_parse_string, 0, &arg_default_smack_process_label },
#else
@@ -764,6 +790,8 @@ static void set_manager_settings(Manager *m) {
m->confirm_spawn = arg_confirm_spawn;
m->service_watchdogs = arg_service_watchdogs;
m->cad_burst_action = arg_cad_burst_action;
+ m->event_loop_ratelimit.interval = arg_event_loop_ratelimit_interval_sec;
+ m->event_loop_ratelimit.burst = arg_event_loop_ratelimit_burst;
manager_set_watchdog(m, WATCHDOG_RUNTIME, arg_runtime_watchdog);
manager_set_watchdog(m, WATCHDOG_REBOOT, arg_reboot_watchdog);
@@ -2495,6 +2523,9 @@ static void reset_arguments(void) {
arg_default_oom_score_adjust_set = false;
arg_default_smack_process_label = mfree(arg_default_smack_process_label);
+ arg_event_loop_ratelimit_interval_sec = 1 * USEC_PER_SEC;
+ arg_event_loop_ratelimit_burst = 50000;
+
}
static void determine_default_oom_score_adjust(void) {
diff --git a/src/core/manager-serialize.c b/src/core/manager-serialize.c
index 74853181b7..125783a48f 100644
--- a/src/core/manager-serialize.c
+++ b/src/core/manager-serialize.c
@@ -166,6 +166,8 @@ int manager_serialize(
(void) serialize_ratelimit(f, "dump-ratelimit", &m->dump_ratelimit);
+ (void) serialize_ratelimit(f, "event-loop-ratelimit", &m->event_loop_ratelimit);
+
bus_track_serialize(m->subscribed, f, "subscribed");
r = dynamic_user_serialize(m, f, fds);
@@ -553,6 +555,8 @@ int manager_deserialize(Manager *m, FILE *f, FDSet *fds) {
(void) varlink_server_deserialize_one(m->varlink_server, val, fds);
} else if ((val = startswith(l, "dump-ratelimit="))) {
deserialize_ratelimit(&m->dump_ratelimit, "dump-ratelimit", val);
+ } else if ((val = startswith(l, "event-loop-ratelimit="))) {
+ deserialize_ratelimit(&m->event_loop_ratelimit, "event-loop-ratelimit", val);
} else {
ManagerTimestamp q;
diff --git a/src/core/manager.c b/src/core/manager.c
index 79408b18dc..ebfc4d3a9a 100644
--- a/src/core/manager.c
+++ b/src/core/manager.c
@@ -3024,7 +3024,6 @@ static int manager_dispatch_jobs_in_progress(sd_event_source *source, usec_t use
}
int manager_loop(Manager *m) {
- RateLimit rl = { .interval = 1*USEC_PER_SEC, .burst = 50000 };
int r;
assert(m);
@@ -3041,7 +3040,7 @@ int manager_loop(Manager *m) {
(void) watchdog_ping();
- if (!ratelimit_below(&rl)) {
+ if (!ratelimit_below(&m->event_loop_ratelimit)) {
/* Yay, something is going seriously wrong, pause a little */
log_warning("Looping too fast. Throttling execution a little.");
sleep(1);
diff --git a/src/core/manager.h b/src/core/manager.h
index 4d5b2e0602..b7917732b5 100644
--- a/src/core/manager.h
+++ b/src/core/manager.h
@@ -465,6 +465,9 @@ struct Manager {
/* Dump*() are slow, so always rate limit them to 10 per 10 minutes */
RateLimit dump_ratelimit;
+
+ /* Rate limit for the manager event loop */
+ RateLimit event_loop_ratelimit;
};
static inline usec_t manager_default_timeout_abort_usec(Manager *m) {
diff --git a/src/core/system.conf.in b/src/core/system.conf.in
index 5d1f6d24f0..31f0f95b7a 100644
--- a/src/core/system.conf.in
+++ b/src/core/system.conf.in
@@ -75,3 +75,5 @@
#DefaultLimitRTTIME=
#DefaultOOMPolicy=stop
#DefaultSmackProcessLabel=
+#EventLoopRateLimitIntervalSec=1s
+#EventLoopRateLimitBurst=50000
diff --git a/src/core/user.conf.in b/src/core/user.conf.in
index b69974978e..0da7ae8be3 100644
--- a/src/core/user.conf.in
+++ b/src/core/user.conf.in
@@ -48,3 +48,5 @@
#DefaultLimitRTPRIO=
#DefaultLimitRTTIME=
#DefaultSmackProcessLabel=
+#EventLoopRateLimitIntervalSec=1s
+#EventLoopRateLimitBurst=50000
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