cgroup v2: DefaultCPUAccounting=yes if CPU controller isn't required

We now don't enable the CPU controller just for CPU accounting if we are
on 4.15+ and using pure unified hierarchy, as this is provided
externally to the CPU controller. This makes CPUAccounting=yes
essentially free, so enabling it by default when it's cheap seems like a
good idea.

diff --git a/man/systemd-system.conf.xml b/man/systemd-system.conf.xml
index ea17111bc59eba7b58c549f301f5b6bee4236b39..35da82ab1a9497b3291ef863d3a3eaecba734b76 100644 (file)
--- a/man/systemd-system.conf.xml
+++ b/man/systemd-system.conf.xml
@@ -307,8 +307,9 @@
         <varname>TasksAccounting=</varname>, <varname>IOAccounting=</varname> and <varname>IPAccounting=</varname>. See
         <citerefentry><refentrytitle>systemd.resource-control</refentrytitle><manvolnum>5</manvolnum></citerefentry>
         for details on the per-unit settings. <varname>DefaultTasksAccounting=</varname> defaults to yes,
-        <varname>DefaultMemoryAccounting=</varname> to &MEMORY_ACCOUNTING_DEFAULT;, the other four settings to
-        no.</para></listitem>
+        <varname>DefaultMemoryAccounting=</varname> to &MEMORY_ACCOUNTING_DEFAULT;. <varname>DefaultCPUAccounting=</varname>
+        defaults to yes if enabling CPU accounting doesn't require the CPU controller to be enabled (Linux 4.15+ using the
+        unified hierarchy for resource control), otherwise it defaults to no. The other three settings default to no.</para></listitem>
       </varlistentry>
 
       <varlistentry>

diff --git a/src/core/main.c b/src/core/main.c
index cabcb9ec165cd51ee269e45ac0d5fa06646a1cd1..f1dad983b722d657db6017ce09f760eecf6d53ff 100644 (file)
--- a/src/core/main.c
+++ b/src/core/main.c
@@ -28,6 +28,7 @@
 #include "bus-error.h"
 #include "bus-util.h"
 #include "capability-util.h"
+#include "cgroup-util.h"
 #include "clock-util.h"
 #include "conf-parser.h"
 #include "cpu-set-util.h"
@@ -119,7 +120,7 @@ static nsec_t arg_timer_slack_nsec = NSEC_INFINITY;
 static usec_t arg_default_timer_accuracy_usec = 1 * USEC_PER_MINUTE;
 static Set* arg_syscall_archs = NULL;
 static FILE* arg_serialization = NULL;
-static bool arg_default_cpu_accounting = false;
+static int arg_default_cpu_accounting = -1;
 static bool arg_default_io_accounting = false;
 static bool arg_default_ip_accounting = false;
 static bool arg_default_blockio_accounting = false;
@@ -702,7 +703,7 @@ static int parse_config_file(void) {
                 { "Manager", "DefaultLimitNICE",          config_parse_rlimit,           RLIMIT_NICE, arg_default_rlimit           },
                 { "Manager", "DefaultLimitRTPRIO",        config_parse_rlimit,           RLIMIT_RTPRIO, arg_default_rlimit         },
                 { "Manager", "DefaultLimitRTTIME",        config_parse_rlimit,           RLIMIT_RTTIME, arg_default_rlimit         },
-                { "Manager", "DefaultCPUAccounting",      config_parse_bool,             0, &arg_default_cpu_accounting            },
+                { "Manager", "DefaultCPUAccounting",      config_parse_tristate,         0, &arg_default_cpu_accounting            },
                 { "Manager", "DefaultIOAccounting",       config_parse_bool,             0, &arg_default_io_accounting             },
                 { "Manager", "DefaultIPAccounting",       config_parse_bool,             0, &arg_default_ip_accounting             },
                 { "Manager", "DefaultBlockIOAccounting",  config_parse_bool,             0, &arg_default_blockio_accounting        },
@@ -751,7 +752,14 @@ static void set_manager_defaults(Manager *m) {
         m->default_restart_usec = arg_default_restart_usec;
         m->default_start_limit_interval = arg_default_start_limit_interval;
         m->default_start_limit_burst = arg_default_start_limit_burst;
-        m->default_cpu_accounting = arg_default_cpu_accounting;
+
+        /* On 4.15+ with unified hierarchy, CPU accounting is essentially free as it doesn't require the CPU
+         * controller to be enabled, so the default is to enable it unless we got told otherwise. */
+        if (arg_default_cpu_accounting >= 0)
+                m->default_cpu_accounting = arg_default_cpu_accounting;
+        else
+                m->default_cpu_accounting = cpu_accounting_is_cheap();
+
         m->default_io_accounting = arg_default_io_accounting;
         m->default_ip_accounting = arg_default_ip_accounting;
         m->default_blockio_accounting = arg_default_blockio_accounting;