core: rearrange cgroup empty events a bit

So far the priorities for cgroup empty event handling were pretty weird.
The raw events (on cgroupsv2 from inotify, on cgroupsv1 from the agent
dgram socket) where scheduled at a lower priority than the cgroup empty
queue dispatcher. Let's swap that and ensure that we can coalesce events
more agressively: let's process the raw events at higher priority than
the cgroup empty event (which remains at the same prio).

diff --git a/src/core/cgroup.c b/src/core/cgroup.c
index ad67ba0..5bac54f 100644 (file)
--- a/src/core/cgroup.c
+++ b/src/core/cgroup.c
@@ -2606,6 +2606,9 @@ int manager_setup_cgroup(Manager *m) {
         if (r < 0)
                 return log_error_errno(r, "Failed to create cgroup empty event source: %m");
 
+        /* Schedule cgroup empty checks early, but after having processed service notification messages or
+         * SIGCHLD signals, so that a cgroup running empty is always just the last safety net of
+         * notification, and we collected the metadata the notification and SIGCHLD stuff offers first. */
         r = sd_event_source_set_priority(m->cgroup_empty_event_source, SD_EVENT_PRIORITY_NORMAL-5);
         if (r < 0)
                 return log_error_errno(r, "Failed to set priority of cgroup empty event source: %m");
@@ -2632,9 +2635,10 @@ int manager_setup_cgroup(Manager *m) {
                 if (r < 0)
                         return log_error_errno(r, "Failed to watch control group inotify object: %m");
 
-                /* Process cgroup empty notifications early, but after service notifications and SIGCHLD. Also
-                 * see handling of cgroup agent notifications, for the classic cgroup hierarchy support. */
-                r = sd_event_source_set_priority(m->cgroup_inotify_event_source, SD_EVENT_PRIORITY_NORMAL-4);
+                /* Process cgroup empty notifications early. Note that when this event is dispatched it'll
+                 * just add the unit to a cgroup empty queue, hence let's run earlier than that. Also see
+                 * handling of cgroup agent notifications, for the classic cgroup hierarchy support. */
+                r = sd_event_source_set_priority(m->cgroup_inotify_event_source, SD_EVENT_PRIORITY_NORMAL-9);
                 if (r < 0)
                         return log_error_errno(r, "Failed to set priority of inotify event source: %m");
 

diff --git a/src/core/manager.c b/src/core/manager.c
index 12ae911..a81c09d 100644 (file)
--- a/src/core/manager.c
+++ b/src/core/manager.c
@@ -992,11 +992,10 @@ static int manager_setup_cgroups_agent(Manager *m) {
                 if (r < 0)
                         return log_error_errno(r, "Failed to allocate cgroups agent event source: %m");
 
-                /* Process cgroups notifications early, but after having processed service notification messages or
-                 * SIGCHLD signals, so that a cgroup running empty is always just the last safety net of notification,
-                 * and we collected the metadata the notification and SIGCHLD stuff offers first. Also see handling of
-                 * cgroup inotify for the unified cgroup stuff. */
-                r = sd_event_source_set_priority(m->cgroups_agent_event_source, SD_EVENT_PRIORITY_NORMAL-4);
+                /* Process cgroups notifications early. Note that when the agent notification is received
+                 * we'll just enqueue the unit in the cgroup empty queue, hence pick a high priority than
+                 * that. Also see handling of cgroup inotify for the unified cgroup stuff. */
+                r = sd_event_source_set_priority(m->cgroups_agent_event_source, SD_EVENT_PRIORITY_NORMAL-9);
                 if (r < 0)
                         return log_error_errno(r, "Failed to set priority of cgroups agent event source: %m");