linux-kernel - Re: [PATCH v3 08/14] sched/core: uclamp: extend cpu's cgroup controller

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Message-ID: <82db1123-339f-0dbf-9332-7e37ee9e4f20@arm.com>
Date:   Fri, 17 Aug 2018 14:21:22 +0200
From:   Dietmar Eggemann <dietmar.eggemann@....com>
To:     Patrick Bellasi <patrick.bellasi@....com>,
        linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org
Cc:     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>,
        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 08/14] sched/core: uclamp: extend cpu's cgroup
 controller

On 08/06/2018 06:39 PM, Patrick Bellasi wrote:

[...]

> Give the above mechanisms, it is now possible to extend the cpu
> controller to specify what is the minimum (or maximum) utilization which
> a task is expected (or allowed) to generate.
> Constraints on minimum and maximum utilization allowed for tasks in a
> CPU cgroup can improve the control on the actual amount of CPU bandwidth
> consumed by tasks.

I assume this is covered by the s/bandwidth/capacity/ you had w/ Juri on 
01/14.

[...]

> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index ff76b000bbe8..2ba55a4afffb 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -1211,6 +1211,74 @@ static inline void uclamp_group_get(struct task_struct *p,
>   	uclamp_group_put(clamp_id, prev_group_id);
>   }
>   
> +#ifdef CONFIG_UCLAMP_TASK_GROUP
> +/**
> + * init_uclamp_sched_group: initialize data structures required for TG's
> + *                          utilization clamping
> + */
> +static inline void init_uclamp_sched_group(void)
> +{
> +	struct uclamp_map *uc_map;
> +	struct uclamp_se *uc_se;
> +	int group_id;
> +	int clamp_id;
> +
> +	/* Root TG's is statically assigned to the first clamp group */
> +	group_id = 0;
> +
> +	/* Initialize root TG's to default (none) clamp values */
> +	for (clamp_id = 0; clamp_id < UCLAMP_CNT; ++clamp_id) {
> +		uc_map = &uclamp_maps[clamp_id][0];
> +
> +		/* Map root TG's clamp value */
> +		uclamp_group_init(clamp_id, group_id, uclamp_none(clamp_id));
> +
> +		/* Init root TG's clamp group */
> +		uc_se = &root_task_group.uclamp[clamp_id];
> +		uc_se->value = uclamp_none(clamp_id);
> +		uc_se->group_id = group_id;
> +
> +		/* Attach root TG's clamp group */
> +		uc_map[group_id].se_count = 1;
> +	}
> +}

Can you not save some lines here:

  static inline void init_uclamp_sched_group(void)
  {
-       struct uclamp_map *uc_map;
         struct uclamp_se *uc_se;
         int group_id;
         int clamp_id;
@@ -1228,8 +1227,6 @@ static inline void init_uclamp_sched_group(void)

         /* Initialize root TG's to default (none) clamp values */
         for (clamp_id = 0; clamp_id < UCLAMP_CNT; ++clamp_id) {
-               uc_map = &uclamp_maps[clamp_id][0];
-
                 /* Map root TG's clamp value */
                 uclamp_group_init(clamp_id, group_id, 
uclamp_none(clamp_id));

@@ -1239,7 +1236,7 @@ static inline void init_uclamp_sched_group(void)
                 uc_se->group_id = group_id;

                 /* Attach root TG's clamp group */
-               uc_map[group_id].se_count = 1;
+               uclamp_maps[clamp_id][group_id].se_count = 1;
         }

This would also make uclamp_group_available() smaller.

[...]