From 0437719c1a97791481c5fd59642494f2108701a8 Mon Sep 17 00:00:00 2001 From: Hao Jia Date: Mon, 7 Aug 2023 11:29:30 +0800 Subject: cgroup/rstat: Record the cumulative per-cpu time of cgroup and its descendants The member variable bstat of the structure cgroup_rstat_cpu records the per-cpu time of the cgroup itself, but does not include the per-cpu time of its descendants. The per-cpu time including descendants is very useful for calculating the per-cpu usage of cgroups. Although we can indirectly obtain the total per-cpu time of the cgroup and its descendants by accumulating the per-cpu bstat of each descendant of the cgroup. But after a child cgroup is removed, we will lose its bstat information. This will cause the cumulative value to be non-monotonic, thus affecting the accuracy of cgroup per-cpu usage. So we add the subtree_bstat variable to record the total per-cpu time of this cgroup and its descendants, which is similar to "cpuacct.usage*" in cgroup v1. And this is also helpful for the migration from cgroup v1 to cgroup v2. After adding this variable, we can obtain the per-cpu time of cgroup and its descendants in user mode through eBPF/drgn, etc. And we are still trying to determine how to expose it in the cgroupfs interface. Suggested-by: Tejun Heo Signed-off-by: Hao Jia Signed-off-by: Tejun Heo --- include/linux/cgroup-defs.h | 14 ++++++++++++++ 1 file changed, 14 insertions(+) (limited to 'include/linux/cgroup-defs.h') diff --git a/include/linux/cgroup-defs.h b/include/linux/cgroup-defs.h index 8a0d5466c7be..7a2862172f51 100644 --- a/include/linux/cgroup-defs.h +++ b/include/linux/cgroup-defs.h @@ -341,6 +341,20 @@ struct cgroup_rstat_cpu { */ struct cgroup_base_stat last_bstat; + /* + * This field is used to record the cumulative per-cpu time of + * the cgroup and its descendants. Currently it can be read via + * eBPF/drgn etc, and we are still trying to determine how to + * expose it in the cgroupfs interface. + */ + struct cgroup_base_stat subtree_bstat; + + /* + * Snapshots at the last reading. These are used to calculate the + * deltas to propagate to the per-cpu subtree_bstat. + */ + struct cgroup_base_stat last_subtree_bstat; + /* * Child cgroups with stat updates on this cpu since the last read * are linked on the parent's ->updated_children through -- cgit v1.2.3