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From: Patrick Bellasi <patrick.bellasi@arm.com>
To: Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc: linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org,
	linux-api@vger.kernel.org, Ingo Molnar <mingo@redhat.com>,
	Peter Zijlstra <peterz@infradead.org>, Tejun Heo <tj@kernel.org>,
	"Rafael J . Wysocki" <rafael.j.wysocki@intel.com>,
	Vincent Guittot <vincent.guittot@linaro.org>,
	Viresh Kumar <viresh.kumar@linaro.org>,
	Paul Turner <pjt@google.com>,
	Quentin Perret <quentin.perret@arm.com>,
	Morten Rasmussen <morten.rasmussen@arm.com>,
	Juri Lelli <juri.lelli@redhat.com>, Todd Kjos <tkjos@google.com>,
	Joel Fernandes <joelaf@google.com>,
	Steve Muckle <smuckle@google.com>,
	Suren Baghdasaryan <surenb@google.com>
Subject: Re: [PATCH v7 01/15] sched/core: uclamp: Add CPU's clamp buckets refcounting
Date: Wed, 13 Mar 2019 15:15:35 +0000	[thread overview]
Message-ID: <20190313151535.q5ivsuywvwkewrk5@e110439-lin> (raw)
In-Reply-To: <21171fa0-7fd5-ebbf-dd48-d6668ed563af@arm.com>

On 12-Mar 13:52, Dietmar Eggemann wrote:
> 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.

Why ?

> 
> [...]
> 
> > +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.

Maybe... can update it in v8

> > +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?

I put it on a different line as a justfication for the loop variable
initialization described in the comment above.

> 
> > +	do {
> > +		--bucket_id;
> > +		if (!rq->uclamp[clamp_id].bucket[bucket_id].tasks)
> 
> if (!bucket[bucket_id].tasks)

Right... that's some leftover from the last refactoring!

[...]

> > + * 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];

I think I went back/forth a couple of times in using pointer or the
extended version, which both have pros and cons.

I personally prefer the pointers as you suggest but I've got the
impression in the past that since everybody cleared "basic C trainings"
it's not so difficult to read the code above too.

> The code in uclamp_rq_inc_id() and uclamp_rq_dec_id() for example becomes
> much more readable.

Agree... let's try to switch once again in v8 and see ;)

> [...]
> 
> >   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?

Since I'm adding a new field at the beginning of the struct, which is
used at enqueue/dequeue time, this is to ensure that all the
callbacks used in these paths are grouped together and don't fall
across a cache line... but yes, that's supposed to be a
micro-optimization which I can skip in this patch.

-- 
#include <best/regards.h>

Patrick Bellasi

  reply	other threads:[~2019-03-13 15:15 UTC|newest]

Thread overview: 84+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-02-08 10:05 [PATCH v7 00/15] Add utilization clamping support Patrick Bellasi
2019-02-08 10:05 ` [PATCH v7 01/15] sched/core: uclamp: Add CPU's clamp buckets refcounting Patrick Bellasi
2019-03-12 12:52   ` Dietmar Eggemann
2019-03-13 15:15     ` Patrick Bellasi [this message]
2019-03-13 21:01       ` Suren Baghdasaryan
2019-03-14 14:54         ` Patrick Bellasi
2019-03-14 15:00       ` Patrick Bellasi
2019-03-12 15:20   ` Peter Zijlstra
2019-03-12 15:50     ` Patrick Bellasi
2019-03-13  8:19       ` Peter Zijlstra
2019-03-13 11:37         ` Patrick Bellasi
2019-03-13 13:40   ` Peter Zijlstra
2019-03-13 16:12     ` Patrick Bellasi
2019-03-13 17:22       ` Peter Zijlstra
2019-03-13 18:22         ` Patrick Bellasi
2019-03-13 19:48       ` Peter Zijlstra
2019-03-14 12:13         ` Patrick Bellasi
2019-03-14 13:32           ` Peter Zijlstra
2019-03-14 15:07             ` Patrick Bellasi
2019-03-14 19:18               ` Peter Zijlstra
2019-03-13 13:52   ` Peter Zijlstra
2019-03-13 15:59     ` Patrick Bellasi
2019-03-13 19:30       ` Peter Zijlstra
2019-03-14 11:03         ` Patrick Bellasi
2019-03-14 13:27           ` Peter Zijlstra
2019-03-13 19:39       ` Peter Zijlstra
2019-03-14 11:18         ` Patrick Bellasi
2019-03-13 21:23     ` Suren Baghdasaryan
2019-03-14 12:43       ` Patrick Bellasi
2019-03-13 14:06   ` Peter Zijlstra
2019-03-13 15:28     ` Patrick Bellasi
2019-03-13 14:09   ` Peter Zijlstra
2019-03-13 15:23     ` Patrick Bellasi
2019-03-13 19:46       ` Peter Zijlstra
2019-03-13 21:08         ` Suren Baghdasaryan
2019-03-14 12:22           ` Patrick Bellasi
2019-03-14 11:45         ` Patrick Bellasi
2019-03-13 21:32   ` Suren Baghdasaryan
2019-03-14 14:46     ` Patrick Bellasi
2019-03-14 15:29       ` Suren Baghdasaryan
2019-03-14 15:40         ` Patrick Bellasi
2019-03-14 16:39           ` Suren Baghdasaryan
2019-02-08 10:05 ` [PATCH v7 02/15] sched/core: uclamp: Enforce last task UCLAMP_MAX Patrick Bellasi
2019-03-13 14:10   ` Peter Zijlstra
2019-03-13 16:20     ` Patrick Bellasi
2019-03-13 17:29       ` Peter Zijlstra
2019-03-13 18:29         ` Patrick Bellasi
2019-03-13 14:12   ` Peter Zijlstra
2019-03-13 16:16     ` Patrick Bellasi
2019-03-14  0:29       ` Suren Baghdasaryan
2019-03-14 17:06         ` Patrick Bellasi
2019-02-08 10:05 ` [PATCH v7 03/15] sched/core: uclamp: Add system default clamps Patrick Bellasi
2019-03-13 14:32   ` Peter Zijlstra
2019-03-13 17:09     ` Patrick Bellasi
2019-03-13 19:58       ` Peter Zijlstra
2019-03-13 20:10       ` Peter Zijlstra
2019-03-15 13:41         ` Patrick Bellasi
2019-03-13 20:13   ` Peter Zijlstra
2019-03-13 20:18   ` Peter Zijlstra
2019-03-18 12:18     ` Patrick Bellasi
2019-03-18 13:10       ` Peter Zijlstra
2019-03-18 14:21         ` Patrick Bellasi
2019-03-18 14:29           ` Peter Zijlstra
2019-02-08 10:05 ` [PATCH v7 04/15] sched/core: Allow sched_setattr() to use the current policy Patrick Bellasi
2019-02-08 10:05 ` [PATCH v7 05/15] sched/core: uclamp: Extend sched_setattr() to support utilization clamping Patrick Bellasi
2019-02-08 10:05 ` [PATCH v7 06/15] sched/core: uclamp: Reset uclamp values on RESET_ON_FORK Patrick Bellasi
2019-03-13 20:52   ` Peter Zijlstra
2019-03-18 12:58     ` Patrick Bellasi
2019-02-08 10:05 ` [PATCH v7 07/15] sched/core: uclamp: Set default clamps for RT tasks Patrick Bellasi
2019-02-08 10:05 ` [PATCH v7 08/15] sched/cpufreq: uclamp: Add clamps for FAIR and " Patrick Bellasi
2019-02-08 10:05 ` [PATCH v7 09/15] sched/core: uclamp: Add uclamp_util_with() Patrick Bellasi
2019-02-08 10:05 ` [PATCH v7 10/15] sched/fair: uclamp: Add uclamp support to energy_compute() Patrick Bellasi
2019-03-06 17:21   ` Quentin Perret
2019-03-18 15:19     ` Patrick Bellasi
2019-02-08 10:05 ` [PATCH v7 11/15] sched/core: uclamp: Extend CPU's cgroup controller Patrick Bellasi
2019-02-14 15:48   ` Tejun Heo
2019-03-19 10:00     ` Patrick Bellasi
2019-02-08 10:05 ` [PATCH v7 12/15] sched/core: uclamp: Propagate parent clamps Patrick Bellasi
2019-03-14 16:17   ` Suren Baghdasaryan
2019-03-18 16:54     ` Patrick Bellasi
2019-03-18 16:58       ` Suren Baghdasaryan
2019-02-08 10:05 ` [PATCH v7 13/15] sched/core: uclamp: Propagate system defaults to root group Patrick Bellasi
2019-02-08 10:05 ` [PATCH v7 14/15] sched/core: uclamp: Use TG's clamps to restrict TASK's clamps Patrick Bellasi
2019-02-08 10:05 ` [PATCH v7 15/15] sched/core: uclamp: Update CPU's refcount on TG's clamp changes Patrick Bellasi

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