Re: [PATCH v3 09/14] sched/core: uclamp: propagate parent clamps

Pavan Kondeti
2018-08-16T09:09:06Z

On Mon, Aug 06, 2018 at 05:39:41PM +0100, Patrick Bellasi wrote:
> In order to properly support hierarchical resources control, the cgroup
> delegation model requires that attribute writes from a child group never
> fail but still are (potentially) constrained based on parent's assigned
> resources. This requires to properly propagate and aggregate parent
> attributes down to its descendants.
>
> Let's implement this mechanism by adding a new "effective" clamp value
> for each task group. The effective clamp value is defined as the smaller
> value between the clamp value of a group and the effective clamp value
> of its parent. This represent also the clamp value which is actually
> used to clamp tasks in each task group.
>
> Since it can be interesting for tasks in a cgroup to know exactly what
> is the currently propagated/enforced configuration, the effective clamp
> values are exposed to user-space by means of a new pair of read-only
> attributes: cpu.util.{min,max}.effective.
>
> Signed-off-by: Patrick Bellasi <patrick.bellasi@arm.com>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Tejun Heo <tj@kernel.org>
> Cc: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> Cc: Viresh Kumar <viresh.kumar@linaro.org>
> Cc: Suren Baghdasaryan <surenb@google.com>
> Cc: Todd Kjos <tkjos@google.com>
> Cc: Joel Fernandes <joelaf@google.com>
> Cc: Juri Lelli <juri.lelli@redhat.com>
> Cc: linux-kernel@vger.kernel.org
> Cc: linux-pm@vger.kernel.org
>

<snip>

> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index 8f48e64fb8a6..3fac2d098084 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -589,6 +589,11 @@ struct uclamp_se {
> unsigned int value;
> /* Utilization clamp group for this constraint */
> unsigned int group_id;
> + /* Effective clamp for tasks in this group */
> + struct {
> + unsigned int value;
> + unsigned int group_id;
> + } effective;
> };

Are these needed when CONFIG_UCLAMP_TASK_GROUP is disabled?

>
> union rcu_special {
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 2ba55a4afffb..f692df3787bd 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -1237,6 +1237,8 @@ static inline void init_uclamp_sched_group(void)
> uc_se = &root_task_group.uclamp[clamp_id];
> uc_se->value = uclamp_none(clamp_id);
> uc_se->group_id = group_id;
> + uc_se->effective.value = uclamp_none(clamp_id);
> + uc_se->effective.group_id = group_id;
>
> /* Attach root TG's clamp group */
> uc_map[group_id].se_count = 1;
>

<snip>

> @@ -7622,11 +7687,19 @@ static struct cftype cpu_legacy_files[] = {
> .read_u64 = cpu_util_min_read_u64,
> .write_u64 = cpu_util_min_write_u64,
> },
> + {
> + .name = "util.min.effective",
> + .read_u64 = cpu_util_min_effective_read_u64,
> + },
> {
> .name = "util.max",
> .read_u64 = cpu_util_max_read_u64,
> .write_u64 = cpu_util_max_write_u64,
> },
> + {
> + .name = "util.max.effective",
> + .read_u64 = cpu_util_max_effective_read_u64,
> + },
> #endif
> { } /* Terminate */
> };

Is there any reason why these are not added for the default hierarchy?

Thanks,
Pavan

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