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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
View file

@ -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

12
kernel/cgroup/rstat.c
View file

@ -344,6 +344,7 @@ static void cgroup_base_stat_flush(struct cgroup *cgrp, int cpu)
{
struct cgroup_rstat_cpu *rstatc = cgroup_rstat_cpu(cgrp, cpu);
struct cgroup *parent = cgroup_parent(cgrp);
struct cgroup_rstat_cpu *prstatc;
struct cgroup_base_stat delta;
unsigned seq;
@ -357,17 +358,24 @@ static void cgroup_base_stat_flush(struct cgroup *cgrp, int cpu)
delta = rstatc->bstat;
} while (__u64_stats_fetch_retry(&rstatc->bsync, seq));
/* propagate percpu delta to global */
/* propagate per-cpu delta to cgroup and per-cpu global statistics */
cgroup_base_stat_sub(&delta, &rstatc->last_bstat);
cgroup_base_stat_add(&cgrp->bstat, &delta);
cgroup_base_stat_add(&rstatc->last_bstat, &delta);
cgroup_base_stat_add(&rstatc->subtree_bstat, &delta);
/* propagate global delta to parent (unless that's root) */
/* propagate cgroup and per-cpu global delta to parent (unless that's root) */
if (cgroup_parent(parent)) {
delta = cgrp->bstat;
cgroup_base_stat_sub(&delta, &cgrp->last_bstat);
cgroup_base_stat_add(&parent->bstat, &delta);
cgroup_base_stat_add(&cgrp->last_bstat, &delta);
delta = rstatc->subtree_bstat;
prstatc = cgroup_rstat_cpu(parent, cpu);
cgroup_base_stat_sub(&delta, &rstatc->last_subtree_bstat);
cgroup_base_stat_add(&prstatc->subtree_bstat, &delta);
cgroup_base_stat_add(&rstatc->last_subtree_bstat, &delta);
}
}