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

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Date:   Thu, 16 Aug 2018 14:39:06 +0530
From:   Pavan Kondeti <pkondeti@...eaurora.org>
To:     Patrick Bellasi <patrick.bellasi@....com>
Cc:     linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Tejun Heo <tj@...nel.org>,
        "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Paul Turner <pjt@...gle.com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Morten Rasmussen <morten.rasmussen@....com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Todd Kjos <tkjos@...gle.com>,
        Joel Fernandes <joelaf@...gle.com>,
        Steve Muckle <smuckle@...gle.com>,
        Suren Baghdasaryan <surenb@...gle.com>
Subject: Re: [PATCH v3 09/14] sched/core: uclamp: propagate parent clamps

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@....com>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Tejun Heo <tj@...nel.org>
> Cc: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> Cc: Viresh Kumar <viresh.kumar@...aro.org>
> Cc: Suren Baghdasaryan <surenb@...gle.com>
> Cc: Todd Kjos <tkjos@...gle.com>
> Cc: Joel Fernandes <joelaf@...gle.com>
> Cc: Juri Lelli <juri.lelli@...hat.com>
> Cc: linux-kernel@...r.kernel.org
> Cc: linux-pm@...r.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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