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SubjectRe: [PATCH v2 03/12] sched/core: uclamp: add CPU's clamp groups accounting
Hi Patrick,

On Mon, Jul 16, 2018 at 1:28 AM, Patrick Bellasi
<patrick.bellasi@arm.com> wrote:
> Utilization clamping allows to clamp the utilization of a CPU within a
> [util_min, util_max] range. This range depends on the set of currently
> RUNNABLE tasks on a CPU, where each task references two "clamp groups"
> defining the util_min and the util_max clamp values to be considered for
> that task. The clamp value mapped by a clamp group applies to a CPU only
> when there is at least one task RUNNABLE referencing that clamp group.
>
> When tasks are enqueued/dequeued on/from a CPU, the set of clamp groups
> active on that CPU can change. Since each clamp group enforces a
> different utilization clamp value, once the set of these groups changes
> it can be required to re-compute what is the new "aggregated" clamp
> value to apply on that CPU.
>
> Clamp values are always MAX aggregated for both util_min and util_max.
> This is to ensure that no tasks can affect the performance of other
> co-scheduled tasks which are either more boosted (i.e. with higher
> util_min clamp) or less capped (i.e. with higher util_max clamp).
>
> Here we introduce the required support to properly reference count clamp
> groups at each task enqueue/dequeue time.
>
> Tasks have a:
> task_struct::uclamp::group_id[clamp_idx]
> indexing, for each clamp index (i.e. util_{min,max}), the clamp group in
> which they should refcount at enqueue time.
>
> CPUs rq have a:
> rq::uclamp::group[clamp_idx][group_idx].tasks
> which is used to reference count how many tasks are currently RUNNABLE on
> that CPU for each clamp group of each clamp index..
>
> The clamp value of each clamp group is tracked by
> rq::uclamp::group[][].value, thus making rq::uclamp::group[][] an
> unordered array of clamp values. However, the MAX aggregation of the
> currently active clamp groups is implemented to minimize the number of
> times we need to scan the complete (unordered) clamp group array to
> figure out the new max value. This operation indeed happens only when we
> dequeue last task of the clamp group corresponding to the current max
> clamp, and thus the CPU is either entering IDLE or going to schedule a
> less boosted or more clamped task.
> Moreover, the expected number of different clamp values, which can be
> configured at build time, is usually so small that a more advanced
> ordering algorithm is not needed. In real use-cases we expect less then
> 10 different values.
>
> Signed-off-by: Patrick Bellasi <patrick.bellasi@arm.com>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Paul Turner <pjt@google.com>
> Cc: Todd Kjos <tkjos@google.com>
> Cc: Joel Fernandes <joelaf@google.com>
> Cc: Juri Lelli <juri.lelli@redhat.com>
> Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
> Cc: Morten Rasmussen <morten.rasmussen@arm.com>
> Cc: linux-kernel@vger.kernel.org
> Cc: linux-pm@vger.kernel.org
> ---
> kernel/sched/core.c | 188 +++++++++++++++++++++++++++++++++++++++++++
> kernel/sched/fair.c | 4 +
> kernel/sched/rt.c | 4 +
> kernel/sched/sched.h | 71 ++++++++++++++++
> 4 files changed, 267 insertions(+)
>
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 50e749067df5..d1969931fea6 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -848,9 +848,19 @@ static inline void uclamp_group_init(int clamp_id, int group_id,
> unsigned int clamp_value)
> {
> struct uclamp_map *uc_map = &uclamp_maps[clamp_id][0];
> + struct uclamp_cpu *uc_cpu;
> + int cpu;
>
> + /* Set clamp group map */
> uc_map[group_id].value = clamp_value;
> uc_map[group_id].se_count = 0;
> +
> + /* Set clamp groups on all CPUs */
> + for_each_possible_cpu(cpu) {
> + uc_cpu = &cpu_rq(cpu)->uclamp;
> + uc_cpu->group[clamp_id][group_id].value = clamp_value;
> + uc_cpu->group[clamp_id][group_id].tasks = 0;
> + }
> }
>
> /**
> @@ -906,6 +916,172 @@ uclamp_group_find(int clamp_id, unsigned int clamp_value)
> return group_id;
> }
>
> +/**
> + * uclamp_cpu_update: updates the utilization clamp of a CPU
> + * @cpu: the CPU which utilization clamp has to be updated
> + * @clamp_id: the clamp index to update
> + *
> + * When tasks are enqueued/dequeued on/from a CPU, the set of currently active
> + * clamp groups is subject to change. Since each clamp group enforces a
> + * different utilization clamp value, once the set of these groups changes it
> + * can be required to re-compute what is the new clamp value to apply for that
> + * CPU.
> + *
> + * For the specified clamp index, this method computes the new CPU utilization
> + * clamp to use until the next change on the set of RUNNABLE tasks on that CPU.
> + */
> +static inline void uclamp_cpu_update(struct rq *rq, int clamp_id)
> +{
> + struct uclamp_group *uc_grp = &rq->uclamp.group[clamp_id][0];
> + int max_value = UCLAMP_NONE;
> + unsigned int group_id;
> +
> + for (group_id = 0; group_id <= CONFIG_UCLAMP_GROUPS_COUNT; ++group_id) {
> + /* Ignore inactive clamp groups, i.e. no RUNNABLE tasks */
> + if (!uclamp_group_active(uc_grp, group_id))
> + continue;
> +
> + /* Both min and max clamp are MAX aggregated */
> + max_value = max(max_value, uc_grp[group_id].value);
> +
> + /* Stop if we reach the max possible clamp */
> + if (max_value >= SCHED_CAPACITY_SCALE)
> + break;
> + }
> + rq->uclamp.value[clamp_id] = max_value;
> +}
> +
> +/**
> + * uclamp_cpu_get_id(): increase reference count for a clamp group on a CPU
> + * @p: the task being enqueued on a CPU
> + * @rq: the CPU's rq where the clamp group has to be reference counted
> + * @clamp_id: the utilization clamp (e.g. min or max utilization) to reference
> + *
> + * Once a task is enqueued on a CPU's RQ, the clamp group currently defined by
> + * the task's uclamp.group_id is reference counted on that CPU.
> + */
> +static inline void uclamp_cpu_get_id(struct task_struct *p,
> + struct rq *rq, int clamp_id)
> +{
> + struct uclamp_group *uc_grp;
> + struct uclamp_cpu *uc_cpu;
> + int clamp_value;
> + int group_id;
> +
> + /* No task specific clamp values: nothing to do */
> + group_id = p->uclamp[clamp_id].group_id;
> + if (group_id == UCLAMP_NONE)
> + return;
> +
> + /* Reference count the task into its current group_id */
> + uc_grp = &rq->uclamp.group[clamp_id][0];
> + uc_grp[group_id].tasks += 1;
> +
> + /*
> + * If this is the new max utilization clamp value, then we can update
> + * straight away the CPU clamp value. Otherwise, the current CPU clamp
> + * value is still valid and we are done.
> + */
> + uc_cpu = &rq->uclamp;
> + clamp_value = p->uclamp[clamp_id].value;
> + if (uc_cpu->value[clamp_id] < clamp_value)
> + uc_cpu->value[clamp_id] = clamp_value;
> +}
> +
> +/**
> + * uclamp_cpu_put_id(): decrease reference count for a clamp group on a CPU
> + * @p: the task being dequeued from a CPU
> + * @cpu: the CPU from where the clamp group has to be released
> + * @clamp_id: the utilization clamp (e.g. min or max utilization) to release
> + *
> + * When a task is dequeued from a CPU's RQ, the CPU's clamp group reference
> + * counted by the task is decreased.
> + * If this was the last task defining the current max clamp group, then the
> + * CPU clamping is updated to find the new max for the specified clamp
> + * index.
> + */
> +static inline void uclamp_cpu_put_id(struct task_struct *p,
> + struct rq *rq, int clamp_id)
> +{
> + struct uclamp_group *uc_grp;
> + struct uclamp_cpu *uc_cpu;
> + unsigned int clamp_value;
> + int group_id;
> +
> + /* No task specific clamp values: nothing to do */
> + group_id = p->uclamp[clamp_id].group_id;
> + if (group_id == UCLAMP_NONE)
> + return;
> +
> + /* Decrement the task's reference counted group index */
> + uc_grp = &rq->uclamp.group[clamp_id][0];
> + uc_grp[group_id].tasks -= 1;
> +
> + /* If this is not the last task, no updates are required */
> + if (uc_grp[group_id].tasks > 0)
> + return;
> +
> + /*
> + * Update the CPU only if this was the last task of the group
> + * defining the current clamp value.
> + */
> + uc_cpu = &rq->uclamp;
> + clamp_value = uc_grp[group_id].value;
> + if (clamp_value >= uc_cpu->value[clamp_id])
> + uclamp_cpu_update(rq, clamp_id);
> +}
> +
> +/**
> + * uclamp_cpu_get(): increase CPU's clamp group refcount
> + * @rq: the CPU's rq where the clamp group has to be refcounted
> + * @p: the task being enqueued
> + *
> + * Once a task is enqueued on a CPU's rq, all the clamp groups currently
> + * enforced on a task are reference counted on that rq.
> + * Not all scheduling classes have utilization clamping support, their tasks
> + * will be silently ignored.
> + *
> + * This method updates the utilization clamp constraints considering the
> + * requirements for the specified task. Thus, this update must be done before
> + * calling into the scheduling classes, which will eventually update schedutil
> + * considering the new task requirements.
> + */
> +static inline void uclamp_cpu_get(struct rq *rq, struct task_struct *p)
> +{
> + int clamp_id;
> +
> + if (unlikely(!p->sched_class->uclamp_enabled))
> + return;
> +
> + for (clamp_id = 0; clamp_id < UCLAMP_CNT; ++clamp_id)
> + uclamp_cpu_get_id(p, rq, clamp_id);
> +}
> +
> +/**
> + * uclamp_cpu_put(): decrease CPU's clamp group refcount
> + * @cpu: the CPU's rq where the clamp group refcount has to be decreased
> + * @p: the task being dequeued
> + *
> + * When a task is dequeued from a CPU's rq, all the clamp groups the task has
> + * been reference counted at task's enqueue time have to be decreased for that
> + * CPU.
> + *
> + * This method updates the utilization clamp constraints considering the
> + * requirements for the specified task. Thus, this update must be done before
> + * calling into the scheduling classes, which will eventually update schedutil
> + * considering the new task requirements.
> + */
> +static inline void uclamp_cpu_put(struct rq *rq, struct task_struct *p)
> +{
> + int clamp_id;
> +
> + if (unlikely(!p->sched_class->uclamp_enabled))
> + return;
> +
> + for (clamp_id = 0; clamp_id < UCLAMP_CNT; ++clamp_id)
> + uclamp_cpu_put_id(p, rq, clamp_id);
> +}
> +
> /**
> * uclamp_group_put: decrease the reference count for a clamp group
> * @clamp_id: the clamp index which was affected by a task group
> @@ -1021,9 +1197,17 @@ static inline int __setscheduler_uclamp(struct task_struct *p,
> static void __init init_uclamp(void)
> {
> int clamp_id;
> + int cpu;
>
> mutex_init(&uclamp_mutex);
>
> + /* Init CPU's clamp groups */
> + for_each_possible_cpu(cpu) {
> + struct uclamp_cpu *uc_cpu = &cpu_rq(cpu)->uclamp;
> +
> + memset(uc_cpu, UCLAMP_NONE, sizeof(struct uclamp_cpu));
> + }
> +
> /* Init SE's clamp map */
> for (clamp_id = 0; clamp_id < UCLAMP_CNT; ++clamp_id) {
> struct uclamp_map *uc_map = &uclamp_maps[clamp_id][0];
> @@ -1037,6 +1221,8 @@ static void __init init_uclamp(void)
> }
>
> #else /* CONFIG_UCLAMP_TASK */
> +static inline void uclamp_cpu_get(struct rq *rq, struct task_struct *p) { }
> +static inline void uclamp_cpu_put(struct rq *rq, struct task_struct *p) { }
> static inline int __setscheduler_uclamp(struct task_struct *p,
> const struct sched_attr *attr)
> {
> @@ -1053,6 +1239,7 @@ static inline void enqueue_task(struct rq *rq, struct task_struct *p, int flags)
> if (!(flags & ENQUEUE_RESTORE))
> sched_info_queued(rq, p);
>
> + uclamp_cpu_get(rq, p);
> p->sched_class->enqueue_task(rq, p, flags);
> }
>
> @@ -1064,6 +1251,7 @@ static inline void dequeue_task(struct rq *rq, struct task_struct *p, int flags)
> if (!(flags & DEQUEUE_SAVE))
> sched_info_dequeued(rq, p);
>
> + uclamp_cpu_put(rq, p);
> p->sched_class->dequeue_task(rq, p, flags);
> }
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 2f0a0be4d344..fd857440276c 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -10433,6 +10433,10 @@ const struct sched_class fair_sched_class = {
> #ifdef CONFIG_FAIR_GROUP_SCHED
> .task_change_group = task_change_group_fair,
> #endif
> +
> +#ifdef CONFIG_UCLAMP_TASK
> + .uclamp_enabled = 1,
> +#endif
> };
>
> #ifdef CONFIG_SCHED_DEBUG
> diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
> index 572567078b60..056a7e1bd529 100644
> --- a/kernel/sched/rt.c
> +++ b/kernel/sched/rt.c
> @@ -2391,6 +2391,10 @@ const struct sched_class rt_sched_class = {
> .switched_to = switched_to_rt,
>
> .update_curr = update_curr_rt,
> +
> +#ifdef CONFIG_UCLAMP_TASK
> + .uclamp_enabled = 1,
> +#endif
> };
>
> #ifdef CONFIG_RT_GROUP_SCHED
> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
> index c7742dcc136c..65bf9ebacd83 100644
> --- a/kernel/sched/sched.h
> +++ b/kernel/sched/sched.h
> @@ -744,6 +744,50 @@ extern void rto_push_irq_work_func(struct irq_work *work);
> #endif
> #endif /* CONFIG_SMP */
>
> +#ifdef CONFIG_UCLAMP_TASK
> +/**
> + * struct uclamp_group - Utilization clamp Group
> + * @value: utilization clamp value for tasks on this clamp group
> + * @tasks: number of RUNNABLE tasks on this clamp group
> + *
> + * Keep track of how many tasks are RUNNABLE for a given utilization
> + * clamp value.
> + */
> +struct uclamp_group {
> + int value;
> + int tasks;
> +};
> +
> +/**
> + * struct uclamp_cpu - CPU's utilization clamp
> + * @value: currently active clamp values for a CPU
> + * @group: utilization clamp groups affecting a CPU
> + *
> + * Keep track of RUNNABLE tasks on a CPUs to aggregate their clamp values.
> + * A clamp value is affecting a CPU where there is at least one task RUNNABLE
> + * (or actually running) with that value.
> + *
> + * We have up to UCLAMP_CNT possible different clamp value, which are
> + * currently only two: minmum utilization and maximum utilization.
> + *
> + * All utilization clamping values are MAX aggregated, since:
> + * - for util_min: we want to run the CPU at least at the max of the minimum
> + * utilization required by its currently RUNNABLE tasks.
> + * - for util_max: we want to allow the CPU to run up to the max of the
> + * maximum utilization allowed by its currently RUNNABLE tasks.
> + *
> + * Since on each system we expect only a limited number of different
> + * utilization clamp values (CONFIG_UCLAMP_GROUPS_COUNT), we use a simple
> + * array to track the metrics required to compute all the per-CPU utilization
> + * clamp values. The additional slot is used to track the default clamp
> + * values, i.e. no min/max clamping at all.
> + */
> +struct uclamp_cpu {
> + int value[UCLAMP_CNT];
> + struct uclamp_group group[UCLAMP_CNT][CONFIG_UCLAMP_GROUPS_COUNT + 1];
> +};
> +#endif /* CONFIG_UCLAMP_TASK */
> +
> /*
> * This is the main, per-CPU runqueue data structure.
> *
> @@ -781,6 +825,11 @@ struct rq {
> unsigned long nr_load_updates;
> u64 nr_switches;
>
> +#ifdef CONFIG_UCLAMP_TASK
> + /* Utilization clamp values based on CPU's RUNNABLE tasks */
> + struct uclamp_cpu uclamp ____cacheline_aligned;
> +#endif
> +
> struct cfs_rq cfs;
> struct rt_rq rt;
> struct dl_rq dl;
> @@ -1535,6 +1584,10 @@ struct sched_class {
> #ifdef CONFIG_FAIR_GROUP_SCHED
> void (*task_change_group)(struct task_struct *p, int type);
> #endif
> +
> +#ifdef CONFIG_UCLAMP_TASK
> + int uclamp_enabled;
> +#endif
> };
>
> static inline void put_prev_task(struct rq *rq, struct task_struct *prev)
> @@ -2130,6 +2183,24 @@ static inline u64 irq_time_read(int cpu)
> }
> #endif /* CONFIG_IRQ_TIME_ACCOUNTING */
>
> +#ifdef CONFIG_UCLAMP_TASK
> +/**
> + * uclamp_group_active: check if a clamp group is active on a CPU
> + * @uc_grp: the clamp groups for a CPU
> + * @group_id: the clamp group to check
> + *
> + * A clamp group affects a CPU if it as at least one RUNNABLE task.

typo: "has at least"

> + *
> + * Return: true if the specified CPU has at least one RUNNABLE task
> + * for the specified clamp group.
> + */
> +static inline bool uclamp_group_active(struct uclamp_group *uc_grp,
> + int group_id)
> +{
> + return uc_grp[group_id].tasks > 0;
> +}
> +#endif /* CONFIG_UCLAMP_TASK */
> +
> #ifdef CONFIG_CPU_FREQ
> DECLARE_PER_CPU(struct update_util_data *, cpufreq_update_util_data);
>
> --
> 2.17.1
>

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