Re: [PATCH v5 1/2] sched, cgroup: Restore meaning to hierarchical_quota

Benjamin Segall
2023-07-11T00:00:19Z

Phil Auld <pauld@redhat.com> writes:

> In cgroupv2 cfs_b->hierarchical_quota is set to -1 for all task
> groups due to the previous fix simply taking the min. It should
> reflect a limit imposed at that level or by an ancestor. Even
> though cgroupv2 does not require child quota to be less than or
> equal to that of its ancestors the task group will still be
> constrained by such a quota so this should be shown here. Cgroupv1
> continues to set this correctly.
>
> In both cases, add initialization when a new task group is created
> based on the current parent's value (or RUNTIME_INF in the case of
> root_task_group). Otherwise, the field is wrong until a quota is
> changed after creation and __cfs_schedulable() is called.

Reviewed-by: Ben Segall <bsegall@google.com>

> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index a68d1276bab0..1b214e10c25d 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -11038,11 +11038,14 @@ static int tg_cfs_schedulable_down(struct task_group *tg, void *data)
>
> /*
> * Ensure max(child_quota) <= parent_quota. On cgroup2,
> - * always take the min. On cgroup1, only inherit when no
> - * limit is set:
> + * always take the non-RUNTIME_INF min. On cgroup1, only
> + * inherit when no limit is set:
> */
> if (cgroup_subsys_on_dfl(cpu_cgrp_subsys)) {
> - quota = min(quota, parent_quota);
> + if (quota == RUNTIME_INF)
> + quota = parent_quota;
> + else if (parent_quota != RUNTIME_INF)
> + quota = min(quota, parent_quota);
> } else {
> if (quota == RUNTIME_INF)
> quota = parent_quota;

I suppose you could also set RUNTIME_INF to be a positive value or
better yet just compare at unsigned, but it's not like config needs to
be fast, so no need to mess with that.

> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 373ff5f55884..92381f9ecf37 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -6005,13 +6005,14 @@ static enum hrtimer_restart sched_cfs_period_timer(struct hrtimer *timer)
> return idle ? HRTIMER_NORESTART : HRTIMER_RESTART;
> }
>
> -void init_cfs_bandwidth(struct cfs_bandwidth *cfs_b)
> +void init_cfs_bandwidth(struct cfs_bandwidth *cfs_b, struct cfs_bandwidth *parent)
> {
> raw_spin_lock_init(&cfs_b->lock);
> cfs_b->runtime = 0;
> cfs_b->quota = RUNTIME_INF;
> cfs_b->period = ns_to_ktime(default_cfs_period());
> cfs_b->burst = 0;
> + cfs_b->hierarchical_quota = ((parent) ? parent->hierarchical_quota : RUNTIME_INF);

Minor style nit: don't need any of these parens here.