Hello.
On Mon, Aug 04, 2025 at 08:29:41PM -0700, Tiffany Yang <ynaffit@xxxxxxxxxx> wrote:
> + cgroup.freeze.stat.local
> + A read-only flat-keyed file which exists in non-root cgroups.
> + The following entry is defined:
> +
> + freeze_time_total
> + Cumulative time that this cgroup has spent between freezing and
> + thawing, regardless of whether by self or ancestor groups.
> + NB: (not) reaching "frozen" state is not accounted here.
> +
> + Using the following ASCII representation of a cgroup's freezer
> + state, ::
> +
> + 1 _____
> + frozen 0 __/ \__
> + ab cd
> +
> + .. Originally contributed by Michal Koutný <mkoutny@xxxxxxxx>
> +
> + the duration being measured is the span between a and c.
This is so little "artwork" that a mere mention in commit message is OK
;-)
> +static int cgroup_freeze_local_stat_show(struct seq_file *seq, void *v)
> +{
> + struct cgroup *cgrp = seq_css(seq)->cgroup;
> + unsigned int sequence;
> + u64 freeze_time;
> +
> + do {
> + sequence = read_seqcount_begin(&cgrp->freezer.freeze_seq);
> + freeze_time = cgrp->freezer.freeze_time_total_ns;
> + /* Add in current freezer interval if the task is now frozen */
Nit: cgrp is frozen, not a task here
> @@ -179,10 +179,16 @@ static void cgroup_do_freeze(struct cgroup *cgrp, bool freeze)
> lockdep_assert_held(&cgroup_mutex);
>
> spin_lock_irq(&css_set_lock);
> - if (freeze)
> + write_seqcount_begin(&cgrp->freezer.freeze_seq);
> + if (freeze) {
> set_bit(CGRP_FREEZE, &cgrp->flags);
> - else
> + cgrp->freezer.freeze_time_start_ns = ktime_get_ns();
I wonder whether it wouldn't achieve more stable results if the
reference timestamp was taken only once in cgroup_freeze().
Measuring the rate of cgroup traversal is rather noise in this case.
Thanks,
Michal
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