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cgroup/rstat: Record the cumulative per-cpu time of cgroup and its descendants

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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 <tj@kernel.org>
Signed-off-by: Hao Jia <jiahao.os@bytedance.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
This commit is contained in:
Hao Jia
2023-08-07 11:29:30 +08:00
committed by Tejun Heo
parent e7e64a1bff
commit 0437719c1a
2 changed files with 24 additions and 2 deletions
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14
include/linux/cgroup-defs.h
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@@ -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