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authorHao Jia <jiahao.os@bytedance.com>2023-08-07 11:29:30 +0800
committerTejun Heo <tj@kernel.org>2023-08-07 08:41:25 -1000
commit0437719c1a97791481c5fd59642494f2108701a8 (patch)
treebfcf3316cae8af8e104241529ba6feb9646d7740 /kernel/cgroup
parente7e64a1bff12f212be12b048723718c2152c4489 (diff)
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 <tj@kernel.org> Signed-off-by: Hao Jia <jiahao.os@bytedance.com> Signed-off-by: Tejun Heo <tj@kernel.org>
Diffstat (limited to 'kernel/cgroup')
-rw-r--r--kernel/cgroup/rstat.c12
1 files changed, 10 insertions, 2 deletions
diff --git a/kernel/cgroup/rstat.c b/kernel/cgroup/rstat.c
index 2542c21b6b6d..d80d7a608141 100644
--- a/kernel/cgroup/rstat.c
+++ b/kernel/cgroup/rstat.c
@@ -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);
}
}