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Message-ID: <21171fa0-7fd5-ebbf-dd48-d6668ed563af@arm.com>
Date: Tue, 12 Mar 2019 13:52:49 +0100
From: Dietmar Eggemann <dietmar.eggemann@....com>
To: Patrick Bellasi <patrick.bellasi@....com>,
linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
linux-api@...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>,
Vincent Guittot <vincent.guittot@...aro.org>,
Viresh Kumar <viresh.kumar@...aro.org>,
Paul Turner <pjt@...gle.com>,
Quentin Perret <quentin.perret@....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 v7 01/15] sched/core: uclamp: Add CPU's clamp buckets
refcounting
On 2/8/19 11:05 AM, Patrick Bellasi wrote:
[...]
> +config UCLAMP_BUCKETS_COUNT
> + int "Number of supported utilization clamp buckets"
> + range 5 20
> + default 5
> + depends on UCLAMP_TASK
> + help
> + Defines the number of clamp buckets to use. The range of each bucket
> + will be SCHED_CAPACITY_SCALE/UCLAMP_BUCKETS_COUNT. The higher the
> + number of clamp buckets the finer their granularity and the higher
> + the precision of clamping aggregation and tracking at run-time.
> +
> + For example, with the default configuration we will have 5 clamp
> + buckets tracking 20% utilization each. A 25% boosted tasks will be
> + refcounted in the [20..39]% bucket and will set the bucket clamp
> + effective value to 25%.
> + If a second 30% boosted task should be co-scheduled on the same CPU,
> + that task will be refcounted in the same bucket of the first task and
> + it will boost the bucket clamp effective value to 30%.
> + The clamp effective value of a bucket is reset to its nominal value
> + (20% in the example above) when there are anymore tasks refcounted in
this sounds weird.
[...]
> +static inline unsigned int uclamp_bucket_value(unsigned int clamp_value)
> +{
> + return UCLAMP_BUCKET_DELTA * uclamp_bucket_id(clamp_value);
> +}
Soemthing like uclamp_bucket_nominal_value() should be clearer.
> +static inline void uclamp_rq_update(struct rq *rq, unsigned int clamp_id)
> +{
> + struct uclamp_bucket *bucket = rq->uclamp[clamp_id].bucket;
> + unsigned int max_value = uclamp_none(clamp_id);
> + unsigned int bucket_id;
unsigned int bucket_id = UCLAMP_BUCKETS;
> +
> + /*
> + * Both min and max clamps are MAX aggregated, thus the topmost
> + * bucket with some tasks defines the rq's clamp value.
> + */
> + bucket_id = UCLAMP_BUCKETS;
to get rid of this line?
> + do {
> + --bucket_id;
> + if (!rq->uclamp[clamp_id].bucket[bucket_id].tasks)
if (!bucket[bucket_id].tasks)
[...]
> +/*
> + * When a task is enqueued on a rq, the clamp bucket currently defined by the
> + * task's uclamp::bucket_id is reference counted on that rq. This also
> + * immediately updates the rq's clamp value if required.
> + *
> + * Since tasks know their specific value requested from user-space, we track
> + * within each bucket the maximum value for tasks refcounted in that bucket.
> + * This provide a further aggregation (local clamping) which allows to track
s/This provide/This provides
> + * within each bucket the exact "requested" clamp value whenever all tasks
> + * RUNNABLE in that bucket require the same clamp.
> + */
> +static inline void uclamp_rq_inc_id(struct task_struct *p, struct rq *rq,
> + unsigned int clamp_id)
> +{
> + unsigned int bucket_id = p->uclamp[clamp_id].bucket_id;
> + unsigned int rq_clamp, bkt_clamp, tsk_clamp;
Wouldn't it be easier to have a pointer to the task's and rq's uclamp
structure as well to the bucket?
- unsigned int bucket_id = p->uclamp[clamp_id].bucket_id;
+ struct uclamp_se *uc_se = &p->uclamp[clamp_id];
+ struct uclamp_rq *uc_rq = &rq->uclamp[clamp_id];
+ struct uclamp_bucket *bucket = &uc_rq->bucket[uc_se->bucket_id];
The code in uclamp_rq_inc_id() and uclamp_rq_dec_id() for example
becomes much more readable.
[...]
> struct sched_class {
> const struct sched_class *next;
>
> +#ifdef CONFIG_UCLAMP_TASK
> + int uclamp_enabled;
> +#endif
> +
> void (*enqueue_task) (struct rq *rq, struct task_struct *p, int flags);
> void (*dequeue_task) (struct rq *rq, struct task_struct *p, int flags);
> - void (*yield_task) (struct rq *rq);
> - bool (*yield_to_task)(struct rq *rq, struct task_struct *p, bool preempt);
>
> void (*check_preempt_curr)(struct rq *rq, struct task_struct *p, int flags);
>
> @@ -1685,7 +1734,6 @@ struct sched_class {
> void (*set_curr_task)(struct rq *rq);
> void (*task_tick)(struct rq *rq, struct task_struct *p, int queued);
> void (*task_fork)(struct task_struct *p);
> - void (*task_dead)(struct task_struct *p);
>
> /*
> * The switched_from() call is allowed to drop rq->lock, therefore we
> @@ -1702,12 +1750,17 @@ struct sched_class {
>
> void (*update_curr)(struct rq *rq);
>
> + void (*yield_task) (struct rq *rq);
> + bool (*yield_to_task)(struct rq *rq, struct task_struct *p, bool preempt);
> +
> #define TASK_SET_GROUP 0
> #define TASK_MOVE_GROUP 1
>
> #ifdef CONFIG_FAIR_GROUP_SCHED
> void (*task_change_group)(struct task_struct *p, int type);
> #endif
> +
> + void (*task_dead)(struct task_struct *p);
Why do you move yield_task, yield_to_task and task_dead here?
[...]
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