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cgroup: add cpu.stat file to root cgroup

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Currently, the root cgroup does not have a cpu.stat file. Add one which
is consistent with /proc/stat to capture global cpu statistics that
might not fall under cgroup accounting.

We haven't done this in the past because the data are already presented
in /proc/stat and we didn't want to add overhead from collecting root
cgroup stats when cgroups are configured, but no cgroups have been
created.

By keeping the data consistent with /proc/stat, I think we avoid the
first problem, while improving the usability of cgroups stats.
We avoid the second problem by computing the contents of cpu.stat from
existing data collected for /proc/stat anyway.

Signed-off-by: Boris Burkov <boris@bur.io>
Suggested-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Tejun Heo <tj@kernel.org>
This commit is contained in:
Boris Burkov 2020-05-27 14:43:19 -07:00 committed by Tejun Heo
parent 6b6ebb3474
commit 936f2a70f2
3 changed files with 53 additions and 12 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

6
Documentation/admin-guide/cgroup-v2.rst
View file

@ -714,9 +714,7 @@ Conventions
- Settings for a single feature should be contained in a single file.
- The root cgroup should be exempt from resource control and thus
shouldn't have resource control interface files. Also,
informational files on the root cgroup which end up showing global
information available elsewhere shouldn't exist.
shouldn't have resource control interface files.
- The default time unit is microseconds. If a different unit is ever
used, an explicit unit suffix must be present.
@ -985,7 +983,7 @@ CPU Interface Files
All time durations are in microseconds.
cpu.stat
A read-only flat-keyed file which exists on non-root cgroups.
A read-only flat-keyed file.
This file exists whether the controller is enabled or not.
It always reports the following three stats:

1
kernel/cgroup/cgroup.c
View file

@ -4874,7 +4874,6 @@ static struct cftype cgroup_base_files[] = {
},
{
.name = "cpu.stat",
.flags = CFTYPE_NOT_ON_ROOT,
.seq_show = cpu_stat_show,
},
#ifdef CONFIG_PSI

52
kernel/cgroup/rstat.c
View file

@ -389,18 +389,62 @@ void __cgroup_account_cputime_field(struct cgroup *cgrp,
cgroup_base_stat_cputime_account_end(cgrp, rstatc);
}
/*
* compute the cputime for the root cgroup by getting the per cpu data
* at a global level, then categorizing the fields in a manner consistent
* with how it is done by __cgroup_account_cputime_field for each bit of
* cpu time attributed to a cgroup.
*/
static void root_cgroup_cputime(struct task_cputime *cputime)
{
int i;
cputime->stime = 0;
cputime->utime = 0;
cputime->sum_exec_runtime = 0;
for_each_possible_cpu(i) {
struct kernel_cpustat kcpustat;
u64 *cpustat = kcpustat.cpustat;
u64 user = 0;
u64 sys = 0;
kcpustat_cpu_fetch(&kcpustat, i);
user += cpustat[CPUTIME_USER];
user += cpustat[CPUTIME_NICE];
cputime->utime += user;
sys += cpustat[CPUTIME_SYSTEM];
sys += cpustat[CPUTIME_IRQ];
sys += cpustat[CPUTIME_SOFTIRQ];
cputime->stime += sys;
cputime->sum_exec_runtime += user;
cputime->sum_exec_runtime += sys;
cputime->sum_exec_runtime += cpustat[CPUTIME_STEAL];
cputime->sum_exec_runtime += cpustat[CPUTIME_GUEST];
cputime->sum_exec_runtime += cpustat[CPUTIME_GUEST_NICE];
}
}
void cgroup_base_stat_cputime_show(struct seq_file *seq)
{
struct cgroup *cgrp = seq_css(seq)->cgroup;
u64 usage, utime, stime;
struct task_cputime cputime;
if (!cgroup_parent(cgrp))
return;
if (cgroup_parent(cgrp)) {
cgroup_rstat_flush_hold(cgrp);
usage = cgrp->bstat.cputime.sum_exec_runtime;
cputime_adjust(&cgrp->bstat.cputime, &cgrp->prev_cputime, &utime, &stime);
cputime_adjust(&cgrp->bstat.cputime, &cgrp->prev_cputime,
&utime, &stime);
cgroup_rstat_flush_release();
} else {
root_cgroup_cputime(&cputime);
usage = cputime.sum_exec_runtime;
utime = cputime.utime;
stime = cputime.stime;
}
do_div(usage, NSEC_PER_USEC);
do_div(utime, NSEC_PER_USEC);