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* [PATCH v10 00/16] Add utilization clamping support
@ 2019-06-21  8:42 Patrick Bellasi
  2019-06-21  8:42 ` [PATCH v10 01/16] sched/core: uclamp: Add CPU's clamp buckets refcounting Patrick Bellasi
                   ` (16 more replies)
  0 siblings, 17 replies; 27+ messages in thread
From: Patrick Bellasi @ 2019-06-21  8:42 UTC (permalink / raw)
  To: linux-kernel, linux-pm
  Cc: Ingo Molnar, Peter Zijlstra, Tejun Heo, Rafael J . Wysocki,
	Vincent Guittot, Viresh Kumar, Paul Turner, Quentin Perret,
	Dietmar Eggemann, Morten Rasmussen, Juri Lelli, Todd Kjos,
	Joel Fernandes, Steve Muckle, Suren Baghdasaryan,
	Alessio Balsini

Hi all, this is a respin of:

  https://lore.kernel.org/lkml/20190515094459.10317-1-patrick.bellasi@arm.com/

which addresses all Tejun's concerns:

 - rename cgroup attributes to be cpu.uclamp.{min,max}
 - update initialization of subgroups clamps to be "no clamps" by default
 - use percentage rational numbers for clamp attributes, e.g. "12.34" for 12.34%.

by introducing modifications impacting only patches:

 [PATCH v10 12/16] sched/core: uclamp: Extend CPU's cgroup controller
 [PATCH v10 13/16] sched/core: uclamp: Propagate parent clamps

The rest of the patches are the same as per in v9, they have been just rebased
on top of:

   tj/cgroup.git	for-5.3
   tip/tip.git		sched/core

AFAIU, all the first 11 patches have been code reviewed and should be at a
"ready to merge" quality level. Please let me know if I'm wrong and there
is something else I need/can to do on those patches.

Otherwise, now that we should have settled all the behavioral aspects, I'm
looking forward for a code review on the last set of patches of this series.

Cheers,
Patrick


Series Organization
===================

The series is organized into these main sections:

 - Patches [01-07]: Per task (primary) API
 - Patches [08-09]: Schedutil integration for FAIR and RT tasks
 - Patches [10-11]: Integration with EAS's energy_compute()
 - Patches [12-16]: Per task group (secondary) API

It is based on today's tj/cgroup/for-5.3 and tip/sched/core and the full tree
is available here:

   git://linux-arm.org/linux-pb.git   lkml/utilclamp_v10
   http://www.linux-arm.org/git?p=linux-pb.git;a=shortlog;h=refs/heads/lkml/utilclamp_v10


Newcomer's Short Abstract
=========================

The Linux scheduler tracks a "utilization" signal for each scheduling entity
(SE), e.g. tasks, to know how much CPU time they use. This signal allows the
scheduler to know how "big" a task is and, in principle, it can support
advanced task placement strategies by selecting the best CPU to run a task.
Some of these strategies are represented by the Energy Aware Scheduler [3].

When the schedutil cpufreq governor is in use, the utilization signal allows
the Linux scheduler to also drive frequency selection. The CPU utilization
signal, which represents the aggregated utilization of tasks scheduled on that
CPU, is used to select the frequency which best fits the workload generated by
the tasks.

The current translation of utilization values into a frequency selection is
simple: we go to max for RT tasks or to the minimum frequency which can
accommodate the utilization of DL+FAIR tasks.
However, utilization values by themselves cannot convey the desired
power/performance behaviors of each task as intended by user-space.
As such they are not ideally suited for task placement decisions.

Task placement and frequency selection policies in the kernel can be improved
by taking into consideration hints coming from authorized user-space elements,
like for example the Android middleware or more generally any "System
Management Software" (SMS) framework.

Utilization clamping is a mechanism which allows to "clamp" (i.e. filter) the
utilization generated by RT and FAIR tasks within a range defined by user-space.
The clamped utilization value can then be used, for example, to enforce a
minimum and/or maximum frequency depending on which tasks are active on a CPU.

The main use-cases for utilization clamping are:

 - boosting: better interactive response for small tasks which
   are affecting the user experience.

   Consider for example the case of a small control thread for an external
   accelerator (e.g. GPU, DSP, other devices). Here, from the task utilization
   the scheduler does not have a complete view of what the task's requirements
   are and, if it's a small utilization task, it keeps selecting a more energy
   efficient CPU, with smaller capacity and lower frequency, thus negatively
   impacting the overall time required to complete task activations.

 - capping: increase energy efficiency for background tasks not affecting the
   user experience.

   Since running on a lower capacity CPU at a lower frequency is more energy
   efficient, when the completion time is not a main goal, then capping the
   utilization considered for certain (maybe big) tasks can have positive
   effects, both on energy consumption and thermal headroom.
   This feature allows also to make RT tasks more energy friendly on mobile
   systems where running them on high capacity CPUs and at the maximum
   frequency is not required.

From these two use-cases, it's worth noticing that frequency selection
biasing, introduced by patches 9 and 10 of this series, is just one possible
usage of utilization clamping. Another compelling extension of utilization
clamping is in helping the scheduler in making tasks placement decisions.

Utilization is (also) a task specific property the scheduler uses to know
how much CPU bandwidth a task requires, at least as long as there is idle time.
Thus, the utilization clamp values, defined either per-task or per-task_group,
can represent tasks to the scheduler as being bigger (or smaller) than what
they actually are.

Utilization clamping thus enables interesting additional optimizations, for
example on asymmetric capacity systems like Arm big.LITTLE and DynamIQ CPUs,
where:

 - boosting: try to run small/foreground tasks on higher-capacity CPUs to
   complete them faster despite being less energy efficient.

 - capping: try to run big/background tasks on low-capacity CPUs to save power
   and thermal headroom for more important tasks

This series does not present this additional usage of utilization clamping but
it's an integral part of the EAS feature set, where [4] is one of its main
components.

Android kernels use SchedTune, a solution similar to utilization clamping, to
bias both 'frequency selection' and 'task placement'. This series provides the
foundation to add similar features to mainline while focusing, for the
time being, just on schedutil integration.


References
==========

[1] Message-ID: <20190509130215.GV2623@hirez.programming.kicks-ass.net>
    https://lore.kernel.org/lkml/20190509130215.GV2623@hirez.programming.kicks-ass.net/

[2] Message-ID: <20180911162827.GJ1100574@devbig004.ftw2.facebook.com>
    https://lore.kernel.org/lkml/20180911162827.GJ1100574@devbig004.ftw2.facebook.com/

[3] Energy Aware Scheduling
    https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/scheduler/sched-energy.txt?h=v5.1

[4] Expressing per-task/per-cgroup performance hints
    Linux Plumbers Conference 2018
    https://linuxplumbersconf.org/event/2/contributions/128/


Patrick Bellasi (16):
  sched/core: uclamp: Add CPU's clamp buckets refcounting
  sched/core: uclamp: Add bucket local max tracking
  sched/core: uclamp: Enforce last task's UCLAMP_MAX
  sched/core: uclamp: Add system default clamps
  sched/core: Allow sched_setattr() to use the current policy
  sched/core: uclamp: Extend sched_setattr() to support utilization
    clamping
  sched/core: uclamp: Reset uclamp values on RESET_ON_FORK
  sched/core: uclamp: Set default clamps for RT tasks
  sched/cpufreq: uclamp: Add clamps for FAIR and RT tasks
  sched/core: uclamp: Add uclamp_util_with()
  sched/fair: uclamp: Add uclamp support to energy_compute()
  sched/core: uclamp: Extend CPU's cgroup controller
  sched/core: uclamp: Propagate parent clamps
  sched/core: uclamp: Propagate system defaults to root group
  sched/core: uclamp: Use TG's clamps to restrict TASK's clamps
  sched/core: uclamp: Update CPU's refcount on TG's clamp changes

 Documentation/admin-guide/cgroup-v2.rst |  50 ++
 include/linux/log2.h                    |  34 +
 include/linux/sched.h                   |  58 ++
 include/linux/sched/sysctl.h            |  11 +
 include/linux/sched/topology.h          |   6 -
 include/uapi/linux/sched.h              |  14 +-
 include/uapi/linux/sched/types.h        |  66 +-
 init/Kconfig                            |  75 +++
 kernel/sched/core.c                     | 797 +++++++++++++++++++++++-
 kernel/sched/cpufreq_schedutil.c        |  22 +-
 kernel/sched/fair.c                     |  44 +-
 kernel/sched/rt.c                       |   4 +
 kernel/sched/sched.h                    | 123 +++-
 kernel/sysctl.c                         |  16 +
 14 files changed, 1276 insertions(+), 44 deletions(-)

-- 
2.21.0


^ permalink raw reply	[flat|nested] 27+ messages in thread

* [PATCH v10 01/16] sched/core: uclamp: Add CPU's clamp buckets refcounting
  2019-06-21  8:42 [PATCH v10 00/16] Add utilization clamping support Patrick Bellasi
@ 2019-06-21  8:42 ` Patrick Bellasi
  2019-06-21  8:42 ` [PATCH v10 02/16] sched/core: uclamp: Add bucket local max tracking Patrick Bellasi
                   ` (15 subsequent siblings)
  16 siblings, 0 replies; 27+ messages in thread
From: Patrick Bellasi @ 2019-06-21  8:42 UTC (permalink / raw)
  To: linux-kernel, linux-pm
  Cc: Ingo Molnar, Peter Zijlstra, Tejun Heo, Rafael J . Wysocki,
	Vincent Guittot, Viresh Kumar, Paul Turner, Quentin Perret,
	Dietmar Eggemann, Morten Rasmussen, Juri Lelli, Todd Kjos,
	Joel Fernandes, Steve Muckle, Suren Baghdasaryan,
	Alessio Balsini

Utilization clamping allows to clamp the CPU's utilization within a
[util_min, util_max] range, depending on the set of RUNNABLE tasks on
that CPU. Each task references two "clamp buckets" defining its minimum
and maximum (util_{min,max}) utilization "clamp values". A CPU's clamp
bucket is active if there is at least one RUNNABLE tasks enqueued on
that CPU and refcounting that bucket.

When a task is {en,de}queued {on,from} a rq, the set of active clamp
buckets on that CPU can change. If the set of active clamp buckets
changes for a CPU a new "aggregated" clamp value is computed for that
CPU. This is because each clamp bucket enforces a different utilization
clamp value.

Clamp values are always MAX aggregated for both util_min and util_max.
This ensures that no task can affect the performance of other
co-scheduled tasks which are more boosted (i.e. with higher util_min
clamp) or less capped (i.e. with higher util_max clamp).

A task has:
   task_struct::uclamp[clamp_id]::bucket_id
to track the "bucket index" of the CPU's clamp bucket it refcounts while
enqueued, for each clamp index (clamp_id).

A runqueue has:
   rq::uclamp[clamp_id]::bucket[bucket_id].tasks
to track how many RUNNABLE tasks on that CPU refcount each
clamp bucket (bucket_id) of a clamp index (clamp_id).
It also has a:
   rq::uclamp[clamp_id]::bucket[bucket_id].value
to track the clamp value of each clamp bucket (bucket_id) of a clamp
index (clamp_id).

The rq::uclamp::bucket[clamp_id][] array is scanned every time it's
needed to find a new MAX aggregated clamp value for a clamp_id. This
operation is required only when it's dequeued the last task of a clamp
bucket tracking the current MAX aggregated clamp value. In this case,
the CPU is either entering IDLE or going to schedule a less boosted or
more clamped task.
The expected number of different clamp values configured at build time
is small enough to fit the full unordered array into a single cache
line, for configurations of up to 7 buckets.

Add to struct rq the basic data structures required to refcount the
number of RUNNABLE tasks for each clamp bucket. Add also the max
aggregation required to update the rq's clamp value at each
enqueue/dequeue event.

Use a simple linear mapping of clamp values into clamp buckets.
Pre-compute and cache bucket_id to avoid integer divisions at
enqueue/dequeue time.

Signed-off-by: Patrick Bellasi <patrick.bellasi@arm.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
---
 include/linux/log2.h           |  34 +++++++
 include/linux/sched.h          |  39 ++++++++
 include/linux/sched/topology.h |   6 --
 init/Kconfig                   |  53 +++++++++++
 kernel/sched/core.c            | 166 +++++++++++++++++++++++++++++++++
 kernel/sched/sched.h           |  51 ++++++++++
 6 files changed, 343 insertions(+), 6 deletions(-)

diff --git a/include/linux/log2.h b/include/linux/log2.h
index 1aec01365ed4..83a4a3ca3e8a 100644
--- a/include/linux/log2.h
+++ b/include/linux/log2.h
@@ -220,4 +220,38 @@ int __order_base_2(unsigned long n)
 		ilog2((n) - 1) + 1) :		\
 	__order_base_2(n)			\
 )
+
+static inline __attribute__((const))
+int __bits_per(unsigned long n)
+{
+	if (n < 2)
+		return 1;
+	if (is_power_of_2(n))
+		return order_base_2(n) + 1;
+	return order_base_2(n);
+}
+
+/**
+ * bits_per - calculate the number of bits required for the argument
+ * @n: parameter
+ *
+ * This is constant-capable and can be used for compile time
+ * initializations, e.g bitfields.
+ *
+ * The first few values calculated by this routine:
+ * bf(0) = 1
+ * bf(1) = 1
+ * bf(2) = 2
+ * bf(3) = 2
+ * bf(4) = 3
+ * ... and so on.
+ */
+#define bits_per(n)				\
+(						\
+	__builtin_constant_p(n) ? (		\
+		((n) == 0 || (n) == 1)		\
+			? 1 : ilog2(n) + 1	\
+	) :					\
+	__bits_per(n)				\
+)
 #endif /* _LINUX_LOG2_H */
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 1b2590a8d038..0027b379fa9b 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -281,6 +281,18 @@ struct vtime {
 	u64			gtime;
 };
 
+/*
+ * Utilization clamp constraints.
+ * @UCLAMP_MIN:	Minimum utilization
+ * @UCLAMP_MAX:	Maximum utilization
+ * @UCLAMP_CNT:	Utilization clamp constraints count
+ */
+enum uclamp_id {
+	UCLAMP_MIN = 0,
+	UCLAMP_MAX,
+	UCLAMP_CNT
+};
+
 struct sched_info {
 #ifdef CONFIG_SCHED_INFO
 	/* Cumulative counters: */
@@ -312,6 +324,10 @@ struct sched_info {
 # define SCHED_FIXEDPOINT_SHIFT		10
 # define SCHED_FIXEDPOINT_SCALE		(1L << SCHED_FIXEDPOINT_SHIFT)
 
+/* Increase resolution of cpu_capacity calculations */
+# define SCHED_CAPACITY_SHIFT		SCHED_FIXEDPOINT_SHIFT
+# define SCHED_CAPACITY_SCALE		(1L << SCHED_CAPACITY_SHIFT)
+
 struct load_weight {
 	unsigned long			weight;
 	u32				inv_weight;
@@ -560,6 +576,25 @@ struct sched_dl_entity {
 	struct hrtimer inactive_timer;
 };
 
+#ifdef CONFIG_UCLAMP_TASK
+/* Number of utilization clamp buckets (shorter alias) */
+#define UCLAMP_BUCKETS CONFIG_UCLAMP_BUCKETS_COUNT
+
+/*
+ * Utilization clamp for a scheduling entity
+ * @value:		clamp value "assigned" to a se
+ * @bucket_id:		bucket index corresponding to the "assigned" value
+ *
+ * The bucket_id is the index of the clamp bucket matching the clamp value
+ * which is pre-computed and stored to avoid expensive integer divisions from
+ * the fast path.
+ */
+struct uclamp_se {
+	unsigned int value		: bits_per(SCHED_CAPACITY_SCALE);
+	unsigned int bucket_id		: bits_per(UCLAMP_BUCKETS);
+};
+#endif /* CONFIG_UCLAMP_TASK */
+
 union rcu_special {
 	struct {
 		u8			blocked;
@@ -640,6 +675,10 @@ struct task_struct {
 #endif
 	struct sched_dl_entity		dl;
 
+#ifdef CONFIG_UCLAMP_TASK
+	struct uclamp_se		uclamp[UCLAMP_CNT];
+#endif
+
 #ifdef CONFIG_PREEMPT_NOTIFIERS
 	/* List of struct preempt_notifier: */
 	struct hlist_head		preempt_notifiers;
diff --git a/include/linux/sched/topology.h b/include/linux/sched/topology.h
index 53afbe07354a..2f8317e55c12 100644
--- a/include/linux/sched/topology.h
+++ b/include/linux/sched/topology.h
@@ -6,12 +6,6 @@
 
 #include <linux/sched/idle.h>
 
-/*
- * Increase resolution of cpu_capacity calculations
- */
-#define SCHED_CAPACITY_SHIFT	SCHED_FIXEDPOINT_SHIFT
-#define SCHED_CAPACITY_SCALE	(1L << SCHED_CAPACITY_SHIFT)
-
 /*
  * sched-domains (multiprocessor balancing) declarations:
  */
diff --git a/init/Kconfig b/init/Kconfig
index 086b72a99d60..bf96faf3fe43 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -677,6 +677,59 @@ config HAVE_UNSTABLE_SCHED_CLOCK
 config GENERIC_SCHED_CLOCK
 	bool
 
+menu "Scheduler features"
+
+config UCLAMP_TASK
+	bool "Enable utilization clamping for RT/FAIR tasks"
+	depends on CPU_FREQ_GOV_SCHEDUTIL
+	help
+	  This feature enables the scheduler to track the clamped utilization
+	  of each CPU based on RUNNABLE tasks scheduled on that CPU.
+
+	  With this option, the user can specify the min and max CPU
+	  utilization allowed for RUNNABLE tasks. The max utilization defines
+	  the maximum frequency a task should use while the min utilization
+	  defines the minimum frequency it should use.
+
+	  Both min and max utilization clamp values are hints to the scheduler,
+	  aiming at improving its frequency selection policy, but they do not
+	  enforce or grant any specific bandwidth for tasks.
+
+	  If in doubt, say N.
+
+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 minimum configuration value 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 no more tasks refcounted in
+	  that bucket.
+
+	  An additional boost/capping margin can be added to some tasks. In the
+	  example above the 25% task will be boosted to 30% until it exits the
+	  CPU. If that should be considered not acceptable on certain systems,
+	  it's always possible to reduce the margin by increasing the number of
+	  clamp buckets to trade off used memory for run-time tracking
+	  precision.
+
+	  If in doubt, use the default value.
+
+endmenu
+
 #
 # For architectures that want to enable the support for NUMA-affine scheduler
 # balancing logic:
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 83bd6bb32a34..bc0389d3e77d 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -761,6 +761,168 @@ static void set_load_weight(struct task_struct *p, bool update_load)
 	}
 }
 
+#ifdef CONFIG_UCLAMP_TASK
+
+/* Integer rounded range for each bucket */
+#define UCLAMP_BUCKET_DELTA DIV_ROUND_CLOSEST(SCHED_CAPACITY_SCALE, UCLAMP_BUCKETS)
+
+#define for_each_clamp_id(clamp_id) \
+	for ((clamp_id) = 0; (clamp_id) < UCLAMP_CNT; (clamp_id)++)
+
+static inline unsigned int uclamp_bucket_id(unsigned int clamp_value)
+{
+	return clamp_value / UCLAMP_BUCKET_DELTA;
+}
+
+static inline unsigned int uclamp_none(int clamp_id)
+{
+	if (clamp_id == UCLAMP_MIN)
+		return 0;
+	return SCHED_CAPACITY_SCALE;
+}
+
+static inline void uclamp_se_set(struct uclamp_se *uc_se, unsigned int value)
+{
+	uc_se->value = value;
+	uc_se->bucket_id = uclamp_bucket_id(value);
+}
+
+static inline
+unsigned int uclamp_rq_max_value(struct rq *rq, unsigned int clamp_id)
+{
+	struct uclamp_bucket *bucket = rq->uclamp[clamp_id].bucket;
+	int bucket_id = UCLAMP_BUCKETS - 1;
+
+	/*
+	 * Since both min and max clamps are max aggregated, find the
+	 * top most bucket with tasks in.
+	 */
+	for ( ; bucket_id >= 0; bucket_id--) {
+		if (!bucket[bucket_id].tasks)
+			continue;
+		return bucket[bucket_id].value;
+	}
+
+	/* No tasks -- default clamp values */
+	return uclamp_none(clamp_id);
+}
+
+/*
+ * When a task is enqueued on a rq, the clamp bucket currently defined by the
+ * task's uclamp::bucket_id is refcounted on that rq. This also immediately
+ * updates the rq's clamp value if required.
+ */
+static inline void uclamp_rq_inc_id(struct rq *rq, struct task_struct *p,
+				    unsigned int clamp_id)
+{
+	struct uclamp_rq *uc_rq = &rq->uclamp[clamp_id];
+	struct uclamp_se *uc_se = &p->uclamp[clamp_id];
+	struct uclamp_bucket *bucket;
+
+	lockdep_assert_held(&rq->lock);
+
+	bucket = &uc_rq->bucket[uc_se->bucket_id];
+	bucket->tasks++;
+
+	if (uc_se->value > READ_ONCE(uc_rq->value))
+		WRITE_ONCE(uc_rq->value, bucket->value);
+}
+
+/*
+ * When a task is dequeued from a rq, the clamp bucket refcounted by the task
+ * is released. If this is the last task reference counting the rq's max
+ * active clamp value, then the rq's clamp value is updated.
+ *
+ * Both refcounted tasks and rq's cached clamp values are expected to be
+ * always valid. If it's detected they are not, as defensive programming,
+ * enforce the expected state and warn.
+ */
+static inline void uclamp_rq_dec_id(struct rq *rq, struct task_struct *p,
+				    unsigned int clamp_id)
+{
+	struct uclamp_rq *uc_rq = &rq->uclamp[clamp_id];
+	struct uclamp_se *uc_se = &p->uclamp[clamp_id];
+	struct uclamp_bucket *bucket;
+	unsigned int rq_clamp;
+
+	lockdep_assert_held(&rq->lock);
+
+	bucket = &uc_rq->bucket[uc_se->bucket_id];
+	SCHED_WARN_ON(!bucket->tasks);
+	if (likely(bucket->tasks))
+		bucket->tasks--;
+
+	if (likely(bucket->tasks))
+		return;
+
+	rq_clamp = READ_ONCE(uc_rq->value);
+	/*
+	 * Defensive programming: this should never happen. If it happens,
+	 * e.g. due to future modification, warn and fixup the expected value.
+	 */
+	SCHED_WARN_ON(bucket->value > rq_clamp);
+	if (bucket->value >= rq_clamp)
+		WRITE_ONCE(uc_rq->value, uclamp_rq_max_value(rq, clamp_id));
+}
+
+static inline void uclamp_rq_inc(struct rq *rq, struct task_struct *p)
+{
+	unsigned int clamp_id;
+
+	if (unlikely(!p->sched_class->uclamp_enabled))
+		return;
+
+	for_each_clamp_id(clamp_id)
+		uclamp_rq_inc_id(rq, p, clamp_id);
+}
+
+static inline void uclamp_rq_dec(struct rq *rq, struct task_struct *p)
+{
+	unsigned int clamp_id;
+
+	if (unlikely(!p->sched_class->uclamp_enabled))
+		return;
+
+	for_each_clamp_id(clamp_id)
+		uclamp_rq_dec_id(rq, p, clamp_id);
+}
+
+static void __init init_uclamp(void)
+{
+	unsigned int clamp_id;
+	int cpu;
+
+	for_each_possible_cpu(cpu) {
+		struct uclamp_bucket *bucket;
+		struct uclamp_rq *uc_rq;
+		unsigned int bucket_id;
+
+		memset(&cpu_rq(cpu)->uclamp, 0, sizeof(struct uclamp_rq));
+
+		for_each_clamp_id(clamp_id) {
+			uc_rq = &cpu_rq(cpu)->uclamp[clamp_id];
+
+			bucket_id = 1;
+			while (bucket_id < UCLAMP_BUCKETS) {
+				bucket = &uc_rq->bucket[bucket_id];
+				bucket->value = bucket_id * UCLAMP_BUCKET_DELTA;
+				++bucket_id;
+			}
+		}
+	}
+
+	for_each_clamp_id(clamp_id) {
+		uclamp_se_set(&init_task.uclamp[clamp_id],
+			      uclamp_none(clamp_id));
+	}
+}
+
+#else /* CONFIG_UCLAMP_TASK */
+static inline void uclamp_rq_inc(struct rq *rq, struct task_struct *p) { }
+static inline void uclamp_rq_dec(struct rq *rq, struct task_struct *p) { }
+static inline void init_uclamp(void) { }
+#endif /* CONFIG_UCLAMP_TASK */
+
 static inline void enqueue_task(struct rq *rq, struct task_struct *p, int flags)
 {
 	if (!(flags & ENQUEUE_NOCLOCK))
@@ -771,6 +933,7 @@ static inline void enqueue_task(struct rq *rq, struct task_struct *p, int flags)
 		psi_enqueue(p, flags & ENQUEUE_WAKEUP);
 	}
 
+	uclamp_rq_inc(rq, p);
 	p->sched_class->enqueue_task(rq, p, flags);
 }
 
@@ -784,6 +947,7 @@ static inline void dequeue_task(struct rq *rq, struct task_struct *p, int flags)
 		psi_dequeue(p, flags & DEQUEUE_SLEEP);
 	}
 
+	uclamp_rq_dec(rq, p);
 	p->sched_class->dequeue_task(rq, p, flags);
 }
 
@@ -6082,6 +6246,8 @@ void __init sched_init(void)
 
 	psi_init();
 
+	init_uclamp();
+
 	scheduler_running = 1;
 }
 
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index b08dee29ef5e..9149d90b8b7c 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -791,6 +791,48 @@ extern void rto_push_irq_work_func(struct irq_work *work);
 #endif
 #endif /* CONFIG_SMP */
 
+#ifdef CONFIG_UCLAMP_TASK
+/*
+ * struct uclamp_bucket - Utilization clamp bucket
+ * @value: utilization clamp value for tasks on this clamp bucket
+ * @tasks: number of RUNNABLE tasks on this clamp bucket
+ *
+ * Keep track of how many tasks are RUNNABLE for a given utilization
+ * clamp value.
+ */
+struct uclamp_bucket {
+	unsigned long value : bits_per(SCHED_CAPACITY_SCALE);
+	unsigned long tasks : BITS_PER_LONG - bits_per(SCHED_CAPACITY_SCALE);
+};
+
+/*
+ * struct uclamp_rq - rq's utilization clamp
+ * @value: currently active clamp values for a rq
+ * @bucket: utilization clamp buckets affecting a rq
+ *
+ * Keep track of RUNNABLE tasks on a rq to aggregate their clamp values.
+ * A clamp value is affecting a rq when there is at least one task RUNNABLE
+ * (or actually running) with that value.
+ *
+ * There are up to UCLAMP_CNT possible different clamp values, currently there
+ * are only two: minimum 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 (UCLAMP_BUCKETS), use a simple array to track
+ * the metrics required to compute all the per-rq utilization clamp values.
+ */
+struct uclamp_rq {
+	unsigned int value;
+	struct uclamp_bucket bucket[UCLAMP_BUCKETS];
+};
+#endif /* CONFIG_UCLAMP_TASK */
+
 /*
  * This is the main, per-CPU runqueue data structure.
  *
@@ -825,6 +867,11 @@ 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_rq	uclamp[UCLAMP_CNT] ____cacheline_aligned;
+#endif
+
 	struct cfs_rq		cfs;
 	struct rt_rq		rt;
 	struct dl_rq		dl;
@@ -1639,6 +1686,10 @@ extern const u32		sched_prio_to_wmult[40];
 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);
-- 
2.21.0


^ permalink raw reply	[flat|nested] 27+ messages in thread

* [PATCH v10 02/16] sched/core: uclamp: Add bucket local max tracking
  2019-06-21  8:42 [PATCH v10 00/16] Add utilization clamping support Patrick Bellasi
  2019-06-21  8:42 ` [PATCH v10 01/16] sched/core: uclamp: Add CPU's clamp buckets refcounting Patrick Bellasi
@ 2019-06-21  8:42 ` Patrick Bellasi
  2019-06-21  8:42 ` [PATCH v10 03/16] sched/core: uclamp: Enforce last task's UCLAMP_MAX Patrick Bellasi
                   ` (14 subsequent siblings)
  16 siblings, 0 replies; 27+ messages in thread
From: Patrick Bellasi @ 2019-06-21  8:42 UTC (permalink / raw)
  To: linux-kernel, linux-pm
  Cc: Ingo Molnar, Peter Zijlstra, Tejun Heo, Rafael J . Wysocki,
	Vincent Guittot, Viresh Kumar, Paul Turner, Quentin Perret,
	Dietmar Eggemann, Morten Rasmussen, Juri Lelli, Todd Kjos,
	Joel Fernandes, Steve Muckle, Suren Baghdasaryan,
	Alessio Balsini

Because of bucketization, different task-specific clamp values are
tracked in the same bucket.  For example, with 20% bucket size and
assuming to have:
  Task1: util_min=25%
  Task2: util_min=35%
both tasks will be refcounted in the [20..39]% bucket and always boosted
only up to 20% thus implementing a simple floor aggregation normally
used in histograms.

In systems with only few and well-defined clamp values, it would be
useful to track the exact clamp value required by a task whenever
possible. For example, if a system requires only 23% and 47% boost
values then it's possible to track the exact boost required by each
task using only 3 buckets of ~33% size each.

Introduce a mechanism to max aggregate the requested clamp values of
RUNNABLE tasks in the same bucket. Keep it simple by resetting the
bucket value to its base value only when a bucket becomes inactive.
Allow a limited and controlled overboosting margin for tasks recounted
in the same bucket.

In systems where the boost values are not known in advance, it is still
possible to control the maximum acceptable overboosting margin by tuning
the number of clamp groups. For example, 20 groups ensure a 5% maximum
overboost.

Remove the rq bucket initialization code since a correct bucket value
is now computed when a task is refcounted into a CPU's rq.

Signed-off-by: Patrick Bellasi <patrick.bellasi@arm.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
---
 kernel/sched/core.c | 43 +++++++++++++++++++++++++------------------
 1 file changed, 25 insertions(+), 18 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index bc0389d3e77d..9c805b83cb36 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -774,6 +774,11 @@ static inline unsigned int uclamp_bucket_id(unsigned int clamp_value)
 	return clamp_value / UCLAMP_BUCKET_DELTA;
 }
 
+static inline unsigned int uclamp_bucket_base_value(unsigned int clamp_value)
+{
+	return UCLAMP_BUCKET_DELTA * uclamp_bucket_id(clamp_value);
+}
+
 static inline unsigned int uclamp_none(int clamp_id)
 {
 	if (clamp_id == UCLAMP_MIN)
@@ -811,6 +816,11 @@ unsigned int uclamp_rq_max_value(struct rq *rq, unsigned int clamp_id)
  * When a task is enqueued on a rq, the clamp bucket currently defined by the
  * task's uclamp::bucket_id is refcounted on that rq. This also immediately
  * updates the rq's clamp value if required.
+ *
+ * Tasks can have a task-specific value requested from user-space, track
+ * within each bucket the maximum value for tasks refcounted in it.
+ * This "local max aggregation" allows to track the exact "requested" value
+ * for each bucket when all its RUNNABLE tasks require the same clamp.
  */
 static inline void uclamp_rq_inc_id(struct rq *rq, struct task_struct *p,
 				    unsigned int clamp_id)
@@ -824,8 +834,15 @@ static inline void uclamp_rq_inc_id(struct rq *rq, struct task_struct *p,
 	bucket = &uc_rq->bucket[uc_se->bucket_id];
 	bucket->tasks++;
 
+	/*
+	 * Local max aggregation: rq buckets always track the max
+	 * "requested" clamp value of its RUNNABLE tasks.
+	 */
+	if (bucket->tasks == 1 || uc_se->value > bucket->value)
+		bucket->value = uc_se->value;
+
 	if (uc_se->value > READ_ONCE(uc_rq->value))
-		WRITE_ONCE(uc_rq->value, bucket->value);
+		WRITE_ONCE(uc_rq->value, uc_se->value);
 }
 
 /*
@@ -852,6 +869,12 @@ static inline void uclamp_rq_dec_id(struct rq *rq, struct task_struct *p,
 	if (likely(bucket->tasks))
 		bucket->tasks--;
 
+	/*
+	 * Keep "local max aggregation" simple and accept to (possibly)
+	 * overboost some RUNNABLE tasks in the same bucket.
+	 * The rq clamp bucket value is reset to its base value whenever
+	 * there are no more RUNNABLE tasks refcounting it.
+	 */
 	if (likely(bucket->tasks))
 		return;
 
@@ -892,25 +915,9 @@ static void __init init_uclamp(void)
 	unsigned int clamp_id;
 	int cpu;
 
-	for_each_possible_cpu(cpu) {
-		struct uclamp_bucket *bucket;
-		struct uclamp_rq *uc_rq;
-		unsigned int bucket_id;
-
+	for_each_possible_cpu(cpu)
 		memset(&cpu_rq(cpu)->uclamp, 0, sizeof(struct uclamp_rq));
 
-		for_each_clamp_id(clamp_id) {
-			uc_rq = &cpu_rq(cpu)->uclamp[clamp_id];
-
-			bucket_id = 1;
-			while (bucket_id < UCLAMP_BUCKETS) {
-				bucket = &uc_rq->bucket[bucket_id];
-				bucket->value = bucket_id * UCLAMP_BUCKET_DELTA;
-				++bucket_id;
-			}
-		}
-	}
-
 	for_each_clamp_id(clamp_id) {
 		uclamp_se_set(&init_task.uclamp[clamp_id],
 			      uclamp_none(clamp_id));
-- 
2.21.0


^ permalink raw reply	[flat|nested] 27+ messages in thread

* [PATCH v10 03/16] sched/core: uclamp: Enforce last task's UCLAMP_MAX
  2019-06-21  8:42 [PATCH v10 00/16] Add utilization clamping support Patrick Bellasi
  2019-06-21  8:42 ` [PATCH v10 01/16] sched/core: uclamp: Add CPU's clamp buckets refcounting Patrick Bellasi
  2019-06-21  8:42 ` [PATCH v10 02/16] sched/core: uclamp: Add bucket local max tracking Patrick Bellasi
@ 2019-06-21  8:42 ` Patrick Bellasi
  2019-06-21  8:42 ` [PATCH v10 04/16] sched/core: uclamp: Add system default clamps Patrick Bellasi
                   ` (13 subsequent siblings)
  16 siblings, 0 replies; 27+ messages in thread
From: Patrick Bellasi @ 2019-06-21  8:42 UTC (permalink / raw)
  To: linux-kernel, linux-pm
  Cc: Ingo Molnar, Peter Zijlstra, Tejun Heo, Rafael J . Wysocki,
	Vincent Guittot, Viresh Kumar, Paul Turner, Quentin Perret,
	Dietmar Eggemann, Morten Rasmussen, Juri Lelli, Todd Kjos,
	Joel Fernandes, Steve Muckle, Suren Baghdasaryan,
	Alessio Balsini

When a task sleeps it removes its max utilization clamp from its CPU.
However, the blocked utilization on that CPU can be higher than the max
clamp value enforced while the task was running. This allows undesired
CPU frequency increases while a CPU is idle, for example, when another
CPU on the same frequency domain triggers a frequency update, since
schedutil can now see the full not clamped blocked utilization of the
idle CPU.

Fix this by using
  uclamp_rq_dec_id(p, rq, UCLAMP_MAX)
    uclamp_rq_max_value(rq, UCLAMP_MAX, clamp_value)
to detect when a CPU has no more RUNNABLE clamped tasks and to flag this
condition.

Don't track any minimum utilization clamps since an idle CPU never
requires a minimum frequency. The decay of the blocked utilization is
good enough to reduce the CPU frequency.

Signed-off-by: Patrick Bellasi <patrick.bellasi@arm.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
---
 kernel/sched/core.c  | 49 +++++++++++++++++++++++++++++++++++++++-----
 kernel/sched/sched.h |  2 ++
 2 files changed, 46 insertions(+), 5 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 9c805b83cb36..b230a3d37263 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -792,8 +792,36 @@ static inline void uclamp_se_set(struct uclamp_se *uc_se, unsigned int value)
 	uc_se->bucket_id = uclamp_bucket_id(value);
 }
 
+static inline unsigned int
+uclamp_idle_value(struct rq *rq, unsigned int clamp_id,
+		  unsigned int clamp_value)
+{
+	/*
+	 * Avoid blocked utilization pushing up the frequency when we go
+	 * idle (which drops the max-clamp) by retaining the last known
+	 * max-clamp.
+	 */
+	if (clamp_id == UCLAMP_MAX) {
+		rq->uclamp_flags |= UCLAMP_FLAG_IDLE;
+		return clamp_value;
+	}
+
+	return uclamp_none(UCLAMP_MIN);
+}
+
+static inline void uclamp_idle_reset(struct rq *rq, unsigned int clamp_id,
+				     unsigned int clamp_value)
+{
+	/* Reset max-clamp retention only on idle exit */
+	if (!(rq->uclamp_flags & UCLAMP_FLAG_IDLE))
+		return;
+
+	WRITE_ONCE(rq->uclamp[clamp_id].value, clamp_value);
+}
+
 static inline
-unsigned int uclamp_rq_max_value(struct rq *rq, unsigned int clamp_id)
+unsigned int uclamp_rq_max_value(struct rq *rq, unsigned int clamp_id,
+				 unsigned int clamp_value)
 {
 	struct uclamp_bucket *bucket = rq->uclamp[clamp_id].bucket;
 	int bucket_id = UCLAMP_BUCKETS - 1;
@@ -809,7 +837,7 @@ unsigned int uclamp_rq_max_value(struct rq *rq, unsigned int clamp_id)
 	}
 
 	/* No tasks -- default clamp values */
-	return uclamp_none(clamp_id);
+	return uclamp_idle_value(rq, clamp_id, clamp_value);
 }
 
 /*
@@ -834,6 +862,8 @@ static inline void uclamp_rq_inc_id(struct rq *rq, struct task_struct *p,
 	bucket = &uc_rq->bucket[uc_se->bucket_id];
 	bucket->tasks++;
 
+	uclamp_idle_reset(rq, clamp_id, uc_se->value);
+
 	/*
 	 * Local max aggregation: rq buckets always track the max
 	 * "requested" clamp value of its RUNNABLE tasks.
@@ -860,6 +890,7 @@ static inline void uclamp_rq_dec_id(struct rq *rq, struct task_struct *p,
 	struct uclamp_rq *uc_rq = &rq->uclamp[clamp_id];
 	struct uclamp_se *uc_se = &p->uclamp[clamp_id];
 	struct uclamp_bucket *bucket;
+	unsigned int bkt_clamp;
 	unsigned int rq_clamp;
 
 	lockdep_assert_held(&rq->lock);
@@ -884,8 +915,10 @@ static inline void uclamp_rq_dec_id(struct rq *rq, struct task_struct *p,
 	 * e.g. due to future modification, warn and fixup the expected value.
 	 */
 	SCHED_WARN_ON(bucket->value > rq_clamp);
-	if (bucket->value >= rq_clamp)
-		WRITE_ONCE(uc_rq->value, uclamp_rq_max_value(rq, clamp_id));
+	if (bucket->value >= rq_clamp) {
+		bkt_clamp = uclamp_rq_max_value(rq, clamp_id, uc_se->value);
+		WRITE_ONCE(uc_rq->value, bkt_clamp);
+	}
 }
 
 static inline void uclamp_rq_inc(struct rq *rq, struct task_struct *p)
@@ -897,6 +930,10 @@ static inline void uclamp_rq_inc(struct rq *rq, struct task_struct *p)
 
 	for_each_clamp_id(clamp_id)
 		uclamp_rq_inc_id(rq, p, clamp_id);
+
+	/* Reset clamp idle holding when there is one RUNNABLE task */
+	if (rq->uclamp_flags & UCLAMP_FLAG_IDLE)
+		rq->uclamp_flags &= ~UCLAMP_FLAG_IDLE;
 }
 
 static inline void uclamp_rq_dec(struct rq *rq, struct task_struct *p)
@@ -915,8 +952,10 @@ static void __init init_uclamp(void)
 	unsigned int clamp_id;
 	int cpu;
 
-	for_each_possible_cpu(cpu)
+	for_each_possible_cpu(cpu) {
 		memset(&cpu_rq(cpu)->uclamp, 0, sizeof(struct uclamp_rq));
+		cpu_rq(cpu)->uclamp_flags = 0;
+	}
 
 	for_each_clamp_id(clamp_id) {
 		uclamp_se_set(&init_task.uclamp[clamp_id],
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 9149d90b8b7c..cd36002436fc 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -870,6 +870,8 @@ struct rq {
 #ifdef CONFIG_UCLAMP_TASK
 	/* Utilization clamp values based on CPU's RUNNABLE tasks */
 	struct uclamp_rq	uclamp[UCLAMP_CNT] ____cacheline_aligned;
+	unsigned int		uclamp_flags;
+#define UCLAMP_FLAG_IDLE 0x01
 #endif
 
 	struct cfs_rq		cfs;
-- 
2.21.0


^ permalink raw reply	[flat|nested] 27+ messages in thread

* [PATCH v10 04/16] sched/core: uclamp: Add system default clamps
  2019-06-21  8:42 [PATCH v10 00/16] Add utilization clamping support Patrick Bellasi
                   ` (2 preceding siblings ...)
  2019-06-21  8:42 ` [PATCH v10 03/16] sched/core: uclamp: Enforce last task's UCLAMP_MAX Patrick Bellasi
@ 2019-06-21  8:42 ` Patrick Bellasi
  2019-06-21  8:42 ` [PATCH v10 05/16] sched/core: Allow sched_setattr() to use the current policy Patrick Bellasi
                   ` (12 subsequent siblings)
  16 siblings, 0 replies; 27+ messages in thread
From: Patrick Bellasi @ 2019-06-21  8:42 UTC (permalink / raw)
  To: linux-kernel, linux-pm
  Cc: Ingo Molnar, Peter Zijlstra, Tejun Heo, Rafael J . Wysocki,
	Vincent Guittot, Viresh Kumar, Paul Turner, Quentin Perret,
	Dietmar Eggemann, Morten Rasmussen, Juri Lelli, Todd Kjos,
	Joel Fernandes, Steve Muckle, Suren Baghdasaryan,
	Alessio Balsini

Tasks without a user-defined clamp value are considered not clamped
and by default their utilization can have any value in the
[0..SCHED_CAPACITY_SCALE] range.

Tasks with a user-defined clamp value are allowed to request any value
in that range, and the required clamp is unconditionally enforced.
However, a "System Management Software" could be interested in limiting
the range of clamp values allowed for all tasks.

Add a privileged interface to define a system default configuration via:

  /proc/sys/kernel/sched_uclamp_util_{min,max}

which works as an unconditional clamp range restriction for all tasks.

With the default configuration, the full SCHED_CAPACITY_SCALE range of
values is allowed for each clamp index. Otherwise, the task-specific
clamp is capped by the corresponding system default value.

Do that by tracking, for each task, the "effective" clamp value and
bucket the task has been refcounted in at enqueue time. This
allows to lazy aggregate "requested" and "system default" values at
enqueue time and simplifies refcounting updates at dequeue time.

The cached bucket ids are used to avoid (relatively) more expensive
integer divisions every time a task is enqueued.

An active flag is used to report when the "effective" value is valid and
thus the task is actually refcounted in the corresponding rq's bucket.

Signed-off-by: Patrick Bellasi <patrick.bellasi@arm.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
---
 include/linux/sched.h        | 10 ++++
 include/linux/sched/sysctl.h | 11 ++++
 kernel/sched/core.c          | 99 +++++++++++++++++++++++++++++++++++-
 kernel/sysctl.c              | 16 ++++++
 4 files changed, 135 insertions(+), 1 deletion(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 0027b379fa9b..af978035ffbe 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -584,14 +584,21 @@ struct sched_dl_entity {
  * Utilization clamp for a scheduling entity
  * @value:		clamp value "assigned" to a se
  * @bucket_id:		bucket index corresponding to the "assigned" value
+ * @active:		the se is currently refcounted in a rq's bucket
  *
  * The bucket_id is the index of the clamp bucket matching the clamp value
  * which is pre-computed and stored to avoid expensive integer divisions from
  * the fast path.
+ *
+ * The active bit is set whenever a task has got an "effective" value assigned,
+ * which can be different from the clamp value "requested" from user-space.
+ * This allows to know a task is refcounted in the rq's bucket corresponding
+ * to the "effective" bucket_id.
  */
 struct uclamp_se {
 	unsigned int value		: bits_per(SCHED_CAPACITY_SCALE);
 	unsigned int bucket_id		: bits_per(UCLAMP_BUCKETS);
+	unsigned int active		: 1;
 };
 #endif /* CONFIG_UCLAMP_TASK */
 
@@ -676,6 +683,9 @@ struct task_struct {
 	struct sched_dl_entity		dl;
 
 #ifdef CONFIG_UCLAMP_TASK
+	/* Clamp values requested for a scheduling entity */
+	struct uclamp_se		uclamp_req[UCLAMP_CNT];
+	/* Effective clamp values used for a scheduling entity */
 	struct uclamp_se		uclamp[UCLAMP_CNT];
 #endif
 
diff --git a/include/linux/sched/sysctl.h b/include/linux/sched/sysctl.h
index 99ce6d728df7..d4f6215ee03f 100644
--- a/include/linux/sched/sysctl.h
+++ b/include/linux/sched/sysctl.h
@@ -56,6 +56,11 @@ int sched_proc_update_handler(struct ctl_table *table, int write,
 extern unsigned int sysctl_sched_rt_period;
 extern int sysctl_sched_rt_runtime;
 
+#ifdef CONFIG_UCLAMP_TASK
+extern unsigned int sysctl_sched_uclamp_util_min;
+extern unsigned int sysctl_sched_uclamp_util_max;
+#endif
+
 #ifdef CONFIG_CFS_BANDWIDTH
 extern unsigned int sysctl_sched_cfs_bandwidth_slice;
 #endif
@@ -75,6 +80,12 @@ extern int sched_rt_handler(struct ctl_table *table, int write,
 		void __user *buffer, size_t *lenp,
 		loff_t *ppos);
 
+#ifdef CONFIG_UCLAMP_TASK
+extern int sysctl_sched_uclamp_handler(struct ctl_table *table, int write,
+				       void __user *buffer, size_t *lenp,
+				       loff_t *ppos);
+#endif
+
 extern int sysctl_numa_balancing(struct ctl_table *table, int write,
 				 void __user *buffer, size_t *lenp,
 				 loff_t *ppos);
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index b230a3d37263..4b8bb6678f16 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -762,6 +762,14 @@ static void set_load_weight(struct task_struct *p, bool update_load)
 }
 
 #ifdef CONFIG_UCLAMP_TASK
+/* Max allowed minimum utilization */
+unsigned int sysctl_sched_uclamp_util_min = SCHED_CAPACITY_SCALE;
+
+/* Max allowed maximum utilization */
+unsigned int sysctl_sched_uclamp_util_max = SCHED_CAPACITY_SCALE;
+
+/* All clamps are required to be less or equal than these values */
+static struct uclamp_se uclamp_default[UCLAMP_CNT];
 
 /* Integer rounded range for each bucket */
 #define UCLAMP_BUCKET_DELTA DIV_ROUND_CLOSEST(SCHED_CAPACITY_SCALE, UCLAMP_BUCKETS)
@@ -840,6 +848,25 @@ unsigned int uclamp_rq_max_value(struct rq *rq, unsigned int clamp_id,
 	return uclamp_idle_value(rq, clamp_id, clamp_value);
 }
 
+/*
+ * The effective clamp bucket index of a task depends on, by increasing
+ * priority:
+ * - the task specific clamp value, when explicitly requested from userspace
+ * - the system default clamp value, defined by the sysadmin
+ */
+static inline struct uclamp_se
+uclamp_eff_get(struct task_struct *p, unsigned int clamp_id)
+{
+	struct uclamp_se uc_req = p->uclamp_req[clamp_id];
+	struct uclamp_se uc_max = uclamp_default[clamp_id];
+
+	/* System default restrictions always apply */
+	if (unlikely(uc_req.value > uc_max.value))
+		return uc_max;
+
+	return uc_req;
+}
+
 /*
  * When a task is enqueued on a rq, the clamp bucket currently defined by the
  * task's uclamp::bucket_id is refcounted on that rq. This also immediately
@@ -859,8 +886,12 @@ static inline void uclamp_rq_inc_id(struct rq *rq, struct task_struct *p,
 
 	lockdep_assert_held(&rq->lock);
 
+	/* Update task effective clamp */
+	p->uclamp[clamp_id] = uclamp_eff_get(p, clamp_id);
+
 	bucket = &uc_rq->bucket[uc_se->bucket_id];
 	bucket->tasks++;
+	uc_se->active = true;
 
 	uclamp_idle_reset(rq, clamp_id, uc_se->value);
 
@@ -899,6 +930,7 @@ static inline void uclamp_rq_dec_id(struct rq *rq, struct task_struct *p,
 	SCHED_WARN_ON(!bucket->tasks);
 	if (likely(bucket->tasks))
 		bucket->tasks--;
+	uc_se->active = false;
 
 	/*
 	 * Keep "local max aggregation" simple and accept to (possibly)
@@ -947,8 +979,65 @@ static inline void uclamp_rq_dec(struct rq *rq, struct task_struct *p)
 		uclamp_rq_dec_id(rq, p, clamp_id);
 }
 
+int sysctl_sched_uclamp_handler(struct ctl_table *table, int write,
+				void __user *buffer, size_t *lenp,
+				loff_t *ppos)
+{
+	int old_min, old_max;
+	static DEFINE_MUTEX(mutex);
+	int result;
+
+	mutex_lock(&mutex);
+	old_min = sysctl_sched_uclamp_util_min;
+	old_max = sysctl_sched_uclamp_util_max;
+
+	result = proc_dointvec(table, write, buffer, lenp, ppos);
+	if (result)
+		goto undo;
+	if (!write)
+		goto done;
+
+	if (sysctl_sched_uclamp_util_min > sysctl_sched_uclamp_util_max ||
+	    sysctl_sched_uclamp_util_max > SCHED_CAPACITY_SCALE) {
+		result = -EINVAL;
+		goto undo;
+	}
+
+	if (old_min != sysctl_sched_uclamp_util_min) {
+		uclamp_se_set(&uclamp_default[UCLAMP_MIN],
+			      sysctl_sched_uclamp_util_min);
+	}
+	if (old_max != sysctl_sched_uclamp_util_max) {
+		uclamp_se_set(&uclamp_default[UCLAMP_MAX],
+			      sysctl_sched_uclamp_util_max);
+	}
+
+	/*
+	 * Updating all the RUNNABLE task is expensive, keep it simple and do
+	 * just a lazy update at each next enqueue time.
+	 */
+	goto done;
+
+undo:
+	sysctl_sched_uclamp_util_min = old_min;
+	sysctl_sched_uclamp_util_max = old_max;
+done:
+	mutex_unlock(&mutex);
+
+	return result;
+}
+
+static void uclamp_fork(struct task_struct *p)
+{
+	unsigned int clamp_id;
+
+	for_each_clamp_id(clamp_id)
+		p->uclamp[clamp_id].active = false;
+}
+
 static void __init init_uclamp(void)
 {
+	struct uclamp_se uc_max = {};
 	unsigned int clamp_id;
 	int cpu;
 
@@ -958,14 +1047,20 @@ static void __init init_uclamp(void)
 	}
 
 	for_each_clamp_id(clamp_id) {
-		uclamp_se_set(&init_task.uclamp[clamp_id],
+		uclamp_se_set(&init_task.uclamp_req[clamp_id],
 			      uclamp_none(clamp_id));
 	}
+
+	/* System defaults allow max clamp values for both indexes */
+	uclamp_se_set(&uc_max, uclamp_none(UCLAMP_MAX));
+	for_each_clamp_id(clamp_id)
+		uclamp_default[clamp_id] = uc_max;
 }
 
 #else /* CONFIG_UCLAMP_TASK */
 static inline void uclamp_rq_inc(struct rq *rq, struct task_struct *p) { }
 static inline void uclamp_rq_dec(struct rq *rq, struct task_struct *p) { }
+static inline void uclamp_fork(struct task_struct *p) { }
 static inline void init_uclamp(void) { }
 #endif /* CONFIG_UCLAMP_TASK */
 
@@ -2534,6 +2629,8 @@ int sched_fork(unsigned long clone_flags, struct task_struct *p)
 	 */
 	p->prio = current->normal_prio;
 
+	uclamp_fork(p);
+
 	/*
 	 * Revert to default priority/policy on fork if requested.
 	 */
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 7d1008be6173..c0b76657e52b 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -457,6 +457,22 @@ static struct ctl_table kern_table[] = {
 		.mode		= 0644,
 		.proc_handler	= sched_rr_handler,
 	},
+#ifdef CONFIG_UCLAMP_TASK
+	{
+		.procname	= "sched_util_clamp_min",
+		.data		= &sysctl_sched_uclamp_util_min,
+		.maxlen		= sizeof(unsigned int),
+		.mode		= 0644,
+		.proc_handler	= sysctl_sched_uclamp_handler,
+	},
+	{
+		.procname	= "sched_util_clamp_max",
+		.data		= &sysctl_sched_uclamp_util_max,
+		.maxlen		= sizeof(unsigned int),
+		.mode		= 0644,
+		.proc_handler	= sysctl_sched_uclamp_handler,
+	},
+#endif
 #ifdef CONFIG_SCHED_AUTOGROUP
 	{
 		.procname	= "sched_autogroup_enabled",
-- 
2.21.0


^ permalink raw reply	[flat|nested] 27+ messages in thread

* [PATCH v10 05/16] sched/core: Allow sched_setattr() to use the current policy
  2019-06-21  8:42 [PATCH v10 00/16] Add utilization clamping support Patrick Bellasi
                   ` (3 preceding siblings ...)
  2019-06-21  8:42 ` [PATCH v10 04/16] sched/core: uclamp: Add system default clamps Patrick Bellasi
@ 2019-06-21  8:42 ` Patrick Bellasi
  2019-06-21  8:42 ` [PATCH v10 06/16] sched/core: uclamp: Extend sched_setattr() to support utilization clamping Patrick Bellasi
                   ` (11 subsequent siblings)
  16 siblings, 0 replies; 27+ messages in thread
From: Patrick Bellasi @ 2019-06-21  8:42 UTC (permalink / raw)
  To: linux-kernel, linux-pm
  Cc: Ingo Molnar, Peter Zijlstra, Tejun Heo, Rafael J . Wysocki,
	Vincent Guittot, Viresh Kumar, Paul Turner, Quentin Perret,
	Dietmar Eggemann, Morten Rasmussen, Juri Lelli, Todd Kjos,
	Joel Fernandes, Steve Muckle, Suren Baghdasaryan,
	Alessio Balsini

The sched_setattr() syscall mandates that a policy is always specified.
This requires to always know which policy a task will have when
attributes are configured and this makes it impossible to add more
generic task attributes valid across different scheduling policies.
Reading the policy before setting generic tasks attributes is racy since
we cannot be sure it is not changed concurrently.

Introduce the required support to change generic task attributes without
affecting the current task policy. This is done by adding an attribute flag
(SCHED_FLAG_KEEP_POLICY) to enforce the usage of the current policy.

Add support for the SETPARAM_POLICY policy, which is already used by the
sched_setparam() POSIX syscall, to the sched_setattr() non-POSIX
syscall.

Signed-off-by: Patrick Bellasi <patrick.bellasi@arm.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
---
 include/uapi/linux/sched.h | 4 +++-
 kernel/sched/core.c        | 2 ++
 2 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/include/uapi/linux/sched.h b/include/uapi/linux/sched.h
index ed4ee170bee2..58b2368d3634 100644
--- a/include/uapi/linux/sched.h
+++ b/include/uapi/linux/sched.h
@@ -51,9 +51,11 @@
 #define SCHED_FLAG_RESET_ON_FORK	0x01
 #define SCHED_FLAG_RECLAIM		0x02
 #define SCHED_FLAG_DL_OVERRUN		0x04
+#define SCHED_FLAG_KEEP_POLICY		0x08
 
 #define SCHED_FLAG_ALL	(SCHED_FLAG_RESET_ON_FORK	| \
 			 SCHED_FLAG_RECLAIM		| \
-			 SCHED_FLAG_DL_OVERRUN)
+			 SCHED_FLAG_DL_OVERRUN		| \
+			 SCHED_FLAG_KEEP_POLICY)
 
 #endif /* _UAPI_LINUX_SCHED_H */
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 4b8bb6678f16..0cf6d9270868 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -4886,6 +4886,8 @@ SYSCALL_DEFINE3(sched_setattr, pid_t, pid, struct sched_attr __user *, uattr,
 
 	if ((int)attr.sched_policy < 0)
 		return -EINVAL;
+	if (attr.sched_flags & SCHED_FLAG_KEEP_POLICY)
+		attr.sched_policy = SETPARAM_POLICY;
 
 	rcu_read_lock();
 	retval = -ESRCH;
-- 
2.21.0


^ permalink raw reply	[flat|nested] 27+ messages in thread

* [PATCH v10 06/16] sched/core: uclamp: Extend sched_setattr() to support utilization clamping
  2019-06-21  8:42 [PATCH v10 00/16] Add utilization clamping support Patrick Bellasi
                   ` (4 preceding siblings ...)
  2019-06-21  8:42 ` [PATCH v10 05/16] sched/core: Allow sched_setattr() to use the current policy Patrick Bellasi
@ 2019-06-21  8:42 ` Patrick Bellasi
  2019-06-21  8:42 ` [PATCH v10 07/16] sched/core: uclamp: Reset uclamp values on RESET_ON_FORK Patrick Bellasi
                   ` (10 subsequent siblings)
  16 siblings, 0 replies; 27+ messages in thread
From: Patrick Bellasi @ 2019-06-21  8:42 UTC (permalink / raw)
  To: linux-kernel, linux-pm
  Cc: Ingo Molnar, Peter Zijlstra, Tejun Heo, Rafael J . Wysocki,
	Vincent Guittot, Viresh Kumar, Paul Turner, Quentin Perret,
	Dietmar Eggemann, Morten Rasmussen, Juri Lelli, Todd Kjos,
	Joel Fernandes, Steve Muckle, Suren Baghdasaryan,
	Alessio Balsini

The SCHED_DEADLINE scheduling class provides an advanced and formal
model to define tasks requirements that can translate into proper
decisions for both task placements and frequencies selections. Other
classes have a more simplified model based on the POSIX concept of
priorities.

Such a simple priority based model however does not allow to exploit
most advanced features of the Linux scheduler like, for example, driving
frequencies selection via the schedutil cpufreq governor. However, also
for non SCHED_DEADLINE tasks, it's still interesting to define tasks
properties to support scheduler decisions.

Utilization clamping exposes to user-space a new set of per-task
attributes the scheduler can use as hints about the expected/required
utilization for a task. This allows to implement a "proactive" per-task
frequency control policy, a more advanced policy than the current one
based just on "passive" measured task utilization. For example, it's
possible to boost interactive tasks (e.g. to get better performance) or
cap background tasks (e.g. to be more energy/thermal efficient).

Introduce a new API to set utilization clamping values for a specified
task by extending sched_setattr(), a syscall which already allows to
define task specific properties for different scheduling classes. A new
pair of attributes allows to specify a minimum and maximum utilization
the scheduler can consider for a task.

Do that by validating the required clamp values before and then applying
the required changes using _the_ same pattern already in use for
__setscheduler(). This ensures that the task is re-enqueued with the new
clamp values.

Signed-off-by: Patrick Bellasi <patrick.bellasi@arm.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
---
 include/linux/sched.h            |  9 ++++
 include/uapi/linux/sched.h       | 12 ++++-
 include/uapi/linux/sched/types.h | 66 +++++++++++++++++++----
 kernel/sched/core.c              | 91 +++++++++++++++++++++++++++++---
 4 files changed, 161 insertions(+), 17 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index af978035ffbe..e2d80e6a187d 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -585,6 +585,7 @@ struct sched_dl_entity {
  * @value:		clamp value "assigned" to a se
  * @bucket_id:		bucket index corresponding to the "assigned" value
  * @active:		the se is currently refcounted in a rq's bucket
+ * @user_defined:	the requested clamp value comes from user-space
  *
  * The bucket_id is the index of the clamp bucket matching the clamp value
  * which is pre-computed and stored to avoid expensive integer divisions from
@@ -594,11 +595,19 @@ struct sched_dl_entity {
  * which can be different from the clamp value "requested" from user-space.
  * This allows to know a task is refcounted in the rq's bucket corresponding
  * to the "effective" bucket_id.
+ *
+ * The user_defined bit is set whenever a task has got a task-specific clamp
+ * value requested from userspace, i.e. the system defaults apply to this task
+ * just as a restriction. This allows to relax default clamps when a less
+ * restrictive task-specific value has been requested, thus allowing to
+ * implement a "nice" semantic. For example, a task running with a 20%
+ * default boost can still drop its own boosting to 0%.
  */
 struct uclamp_se {
 	unsigned int value		: bits_per(SCHED_CAPACITY_SCALE);
 	unsigned int bucket_id		: bits_per(UCLAMP_BUCKETS);
 	unsigned int active		: 1;
+	unsigned int user_defined	: 1;
 };
 #endif /* CONFIG_UCLAMP_TASK */
 
diff --git a/include/uapi/linux/sched.h b/include/uapi/linux/sched.h
index 58b2368d3634..617bb59aa8ba 100644
--- a/include/uapi/linux/sched.h
+++ b/include/uapi/linux/sched.h
@@ -52,10 +52,20 @@
 #define SCHED_FLAG_RECLAIM		0x02
 #define SCHED_FLAG_DL_OVERRUN		0x04
 #define SCHED_FLAG_KEEP_POLICY		0x08
+#define SCHED_FLAG_KEEP_PARAMS		0x10
+#define SCHED_FLAG_UTIL_CLAMP_MIN	0x20
+#define SCHED_FLAG_UTIL_CLAMP_MAX	0x40
+
+#define SCHED_FLAG_KEEP_ALL	(SCHED_FLAG_KEEP_POLICY | \
+				 SCHED_FLAG_KEEP_PARAMS)
+
+#define SCHED_FLAG_UTIL_CLAMP	(SCHED_FLAG_UTIL_CLAMP_MIN | \
+				 SCHED_FLAG_UTIL_CLAMP_MAX)
 
 #define SCHED_FLAG_ALL	(SCHED_FLAG_RESET_ON_FORK	| \
 			 SCHED_FLAG_RECLAIM		| \
 			 SCHED_FLAG_DL_OVERRUN		| \
-			 SCHED_FLAG_KEEP_POLICY)
+			 SCHED_FLAG_KEEP_ALL		| \
+			 SCHED_FLAG_UTIL_CLAMP)
 
 #endif /* _UAPI_LINUX_SCHED_H */
diff --git a/include/uapi/linux/sched/types.h b/include/uapi/linux/sched/types.h
index 10fbb8031930..c852153ddb0d 100644
--- a/include/uapi/linux/sched/types.h
+++ b/include/uapi/linux/sched/types.h
@@ -9,6 +9,7 @@ struct sched_param {
 };
 
 #define SCHED_ATTR_SIZE_VER0	48	/* sizeof first published struct */
+#define SCHED_ATTR_SIZE_VER1	56	/* add: util_{min,max} */
 
 /*
  * Extended scheduling parameters data structure.
@@ -21,8 +22,33 @@ struct sched_param {
  * the tasks may be useful for a wide variety of application fields, e.g.,
  * multimedia, streaming, automation and control, and many others.
  *
- * This variant (sched_attr) is meant at describing a so-called
- * sporadic time-constrained task. In such model a task is specified by:
+ * This variant (sched_attr) allows to define additional attributes to
+ * improve the scheduler knowledge about task requirements.
+ *
+ * Scheduling Class Attributes
+ * ===========================
+ *
+ * A subset of sched_attr attributes specifies the
+ * scheduling policy and relative POSIX attributes:
+ *
+ *  @size		size of the structure, for fwd/bwd compat.
+ *
+ *  @sched_policy	task's scheduling policy
+ *  @sched_nice		task's nice value      (SCHED_NORMAL/BATCH)
+ *  @sched_priority	task's static priority (SCHED_FIFO/RR)
+ *
+ * Certain more advanced scheduling features can be controlled by a
+ * predefined set of flags via the attribute:
+ *
+ *  @sched_flags	for customizing the scheduler behaviour
+ *
+ * Sporadic Time-Constrained Task Attributes
+ * =========================================
+ *
+ * A subset of sched_attr attributes allows to describe a so-called
+ * sporadic time-constrained task.
+ *
+ * In such a model a task is specified by:
  *  - the activation period or minimum instance inter-arrival time;
  *  - the maximum (or average, depending on the actual scheduling
  *    discipline) computation time of all instances, a.k.a. runtime;
@@ -34,14 +60,8 @@ struct sched_param {
  * than the runtime and must be completed by time instant t equal to
  * the instance activation time + the deadline.
  *
- * This is reflected by the actual fields of the sched_attr structure:
+ * This is reflected by the following fields of the sched_attr structure:
  *
- *  @size		size of the structure, for fwd/bwd compat.
- *
- *  @sched_policy	task's scheduling policy
- *  @sched_flags	for customizing the scheduler behaviour
- *  @sched_nice		task's nice value      (SCHED_NORMAL/BATCH)
- *  @sched_priority	task's static priority (SCHED_FIFO/RR)
  *  @sched_deadline	representative of the task's deadline
  *  @sched_runtime	representative of the task's runtime
  *  @sched_period	representative of the task's period
@@ -53,6 +73,29 @@ struct sched_param {
  * As of now, the SCHED_DEADLINE policy (sched_dl scheduling class) is the
  * only user of this new interface. More information about the algorithm
  * available in the scheduling class file or in Documentation/.
+ *
+ * Task Utilization Attributes
+ * ===========================
+ *
+ * A subset of sched_attr attributes allows to specify the utilization
+ * expected for a task. These attributes allow to inform the scheduler about
+ * the utilization boundaries within which it should schedule the task. These
+ * boundaries are valuable hints to support scheduler decisions on both task
+ * placement and frequency selection.
+ *
+ *  @sched_util_min	represents the minimum utilization
+ *  @sched_util_max	represents the maximum utilization
+ *
+ * Utilization is a value in the range [0..SCHED_CAPACITY_SCALE]. It
+ * represents the percentage of CPU time used by a task when running at the
+ * maximum frequency on the highest capacity CPU of the system. For example, a
+ * 20% utilization task is a task running for 2ms every 10ms at maximum
+ * frequency.
+ *
+ * A task with a min utilization value bigger than 0 is more likely scheduled
+ * on a CPU with a capacity big enough to fit the specified value.
+ * A task with a max utilization value smaller than 1024 is more likely
+ * scheduled on a CPU with no more capacity than the specified value.
  */
 struct sched_attr {
 	__u32 size;
@@ -70,6 +113,11 @@ struct sched_attr {
 	__u64 sched_runtime;
 	__u64 sched_deadline;
 	__u64 sched_period;
+
+	/* Utilization hints */
+	__u32 sched_util_min;
+	__u32 sched_util_max;
+
 };
 
 #endif /* _UAPI_LINUX_SCHED_TYPES_H */
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 0cf6d9270868..7d4272440890 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -794,10 +794,12 @@ static inline unsigned int uclamp_none(int clamp_id)
 	return SCHED_CAPACITY_SCALE;
 }
 
-static inline void uclamp_se_set(struct uclamp_se *uc_se, unsigned int value)
+static inline void uclamp_se_set(struct uclamp_se *uc_se,
+				 unsigned int value, bool user_defined)
 {
 	uc_se->value = value;
 	uc_se->bucket_id = uclamp_bucket_id(value);
+	uc_se->user_defined = user_defined;
 }
 
 static inline unsigned int
@@ -1005,11 +1007,11 @@ int sysctl_sched_uclamp_handler(struct ctl_table *table, int write,
 
 	if (old_min != sysctl_sched_uclamp_util_min) {
 		uclamp_se_set(&uclamp_default[UCLAMP_MIN],
-			      sysctl_sched_uclamp_util_min);
+			      sysctl_sched_uclamp_util_min, false);
 	}
 	if (old_max != sysctl_sched_uclamp_util_max) {
 		uclamp_se_set(&uclamp_default[UCLAMP_MAX],
-			      sysctl_sched_uclamp_util_max);
+			      sysctl_sched_uclamp_util_max, false);
 	}
 
 	/*
@@ -1027,6 +1029,42 @@ int sysctl_sched_uclamp_handler(struct ctl_table *table, int write,
 	return result;
 }
 
+static int uclamp_validate(struct task_struct *p,
+			   const struct sched_attr *attr)
+{
+	unsigned int lower_bound = p->uclamp_req[UCLAMP_MIN].value;
+	unsigned int upper_bound = p->uclamp_req[UCLAMP_MAX].value;
+
+	if (attr->sched_flags & SCHED_FLAG_UTIL_CLAMP_MIN)
+		lower_bound = attr->sched_util_min;
+	if (attr->sched_flags & SCHED_FLAG_UTIL_CLAMP_MAX)
+		upper_bound = attr->sched_util_max;
+
+	if (lower_bound > upper_bound)
+		return -EINVAL;
+	if (upper_bound > SCHED_CAPACITY_SCALE)
+		return -EINVAL;
+
+	return 0;
+}
+
+static void __setscheduler_uclamp(struct task_struct *p,
+				  const struct sched_attr *attr)
+{
+	if (likely(!(attr->sched_flags & SCHED_FLAG_UTIL_CLAMP)))
+		return;
+
+	if (attr->sched_flags & SCHED_FLAG_UTIL_CLAMP_MIN) {
+		uclamp_se_set(&p->uclamp_req[UCLAMP_MIN],
+			      attr->sched_util_min, true);
+	}
+
+	if (attr->sched_flags & SCHED_FLAG_UTIL_CLAMP_MAX) {
+		uclamp_se_set(&p->uclamp_req[UCLAMP_MAX],
+			      attr->sched_util_max, true);
+	}
+}
+
 static void uclamp_fork(struct task_struct *p)
 {
 	unsigned int clamp_id;
@@ -1048,11 +1086,11 @@ static void __init init_uclamp(void)
 
 	for_each_clamp_id(clamp_id) {
 		uclamp_se_set(&init_task.uclamp_req[clamp_id],
-			      uclamp_none(clamp_id));
+			      uclamp_none(clamp_id), false);
 	}
 
 	/* System defaults allow max clamp values for both indexes */
-	uclamp_se_set(&uc_max, uclamp_none(UCLAMP_MAX));
+	uclamp_se_set(&uc_max, uclamp_none(UCLAMP_MAX), false);
 	for_each_clamp_id(clamp_id)
 		uclamp_default[clamp_id] = uc_max;
 }
@@ -1060,6 +1098,13 @@ static void __init init_uclamp(void)
 #else /* CONFIG_UCLAMP_TASK */
 static inline void uclamp_rq_inc(struct rq *rq, struct task_struct *p) { }
 static inline void uclamp_rq_dec(struct rq *rq, struct task_struct *p) { }
+static inline int uclamp_validate(struct task_struct *p,
+				  const struct sched_attr *attr)
+{
+	return -EOPNOTSUPP;
+}
+static void __setscheduler_uclamp(struct task_struct *p,
+				  const struct sched_attr *attr) { }
 static inline void uclamp_fork(struct task_struct *p) { }
 static inline void init_uclamp(void) { }
 #endif /* CONFIG_UCLAMP_TASK */
@@ -4401,6 +4446,13 @@ static void __setscheduler_params(struct task_struct *p,
 static void __setscheduler(struct rq *rq, struct task_struct *p,
 			   const struct sched_attr *attr, bool keep_boost)
 {
+	/*
+	 * If params can't change scheduling class changes aren't allowed
+	 * either.
+	 */
+	if (attr->sched_flags & SCHED_FLAG_KEEP_PARAMS)
+		return;
+
 	__setscheduler_params(p, attr);
 
 	/*
@@ -4538,6 +4590,13 @@ static int __sched_setscheduler(struct task_struct *p,
 			return retval;
 	}
 
+	/* Update task specific "requested" clamps */
+	if (attr->sched_flags & SCHED_FLAG_UTIL_CLAMP) {
+		retval = uclamp_validate(p, attr);
+		if (retval)
+			return retval;
+	}
+
 	/*
 	 * Make sure no PI-waiters arrive (or leave) while we are
 	 * changing the priority of the task:
@@ -4567,6 +4626,8 @@ static int __sched_setscheduler(struct task_struct *p,
 			goto change;
 		if (dl_policy(policy) && dl_param_changed(p, attr))
 			goto change;
+		if (attr->sched_flags & SCHED_FLAG_UTIL_CLAMP)
+			goto change;
 
 		p->sched_reset_on_fork = reset_on_fork;
 		task_rq_unlock(rq, p, &rf);
@@ -4647,7 +4708,9 @@ static int __sched_setscheduler(struct task_struct *p,
 		put_prev_task(rq, p);
 
 	prev_class = p->sched_class;
+
 	__setscheduler(rq, p, attr, pi);
+	__setscheduler_uclamp(p, attr);
 
 	if (queued) {
 		/*
@@ -4823,6 +4886,10 @@ static int sched_copy_attr(struct sched_attr __user *uattr, struct sched_attr *a
 	if (ret)
 		return -EFAULT;
 
+	if ((attr->sched_flags & SCHED_FLAG_UTIL_CLAMP) &&
+	    size < SCHED_ATTR_SIZE_VER1)
+		return -EINVAL;
+
 	/*
 	 * XXX: Do we want to be lenient like existing syscalls; or do we want
 	 * to be strict and return an error on out-of-bounds values?
@@ -4892,10 +4959,15 @@ SYSCALL_DEFINE3(sched_setattr, pid_t, pid, struct sched_attr __user *, uattr,
 	rcu_read_lock();
 	retval = -ESRCH;
 	p = find_process_by_pid(pid);
-	if (p != NULL)
-		retval = sched_setattr(p, &attr);
+	if (likely(p))
+		get_task_struct(p);
 	rcu_read_unlock();
 
+	if (likely(p)) {
+		retval = sched_setattr(p, &attr);
+		put_task_struct(p);
+	}
+
 	return retval;
 }
 
@@ -5046,6 +5118,11 @@ SYSCALL_DEFINE4(sched_getattr, pid_t, pid, struct sched_attr __user *, uattr,
 	else
 		attr.sched_nice = task_nice(p);
 
+#ifdef CONFIG_UCLAMP_TASK
+	attr.sched_util_min = p->uclamp_req[UCLAMP_MIN].value;
+	attr.sched_util_max = p->uclamp_req[UCLAMP_MAX].value;
+#endif
+
 	rcu_read_unlock();
 
 	retval = sched_read_attr(uattr, &attr, size);
-- 
2.21.0


^ permalink raw reply	[flat|nested] 27+ messages in thread

* [PATCH v10 07/16] sched/core: uclamp: Reset uclamp values on RESET_ON_FORK
  2019-06-21  8:42 [PATCH v10 00/16] Add utilization clamping support Patrick Bellasi
                   ` (5 preceding siblings ...)
  2019-06-21  8:42 ` [PATCH v10 06/16] sched/core: uclamp: Extend sched_setattr() to support utilization clamping Patrick Bellasi
@ 2019-06-21  8:42 ` Patrick Bellasi
  2019-06-21  8:42 ` [PATCH v10 08/16] sched/core: uclamp: Set default clamps for RT tasks Patrick Bellasi
                   ` (9 subsequent siblings)
  16 siblings, 0 replies; 27+ messages in thread
From: Patrick Bellasi @ 2019-06-21  8:42 UTC (permalink / raw)
  To: linux-kernel, linux-pm
  Cc: Ingo Molnar, Peter Zijlstra, Tejun Heo, Rafael J . Wysocki,
	Vincent Guittot, Viresh Kumar, Paul Turner, Quentin Perret,
	Dietmar Eggemann, Morten Rasmussen, Juri Lelli, Todd Kjos,
	Joel Fernandes, Steve Muckle, Suren Baghdasaryan,
	Alessio Balsini

A forked tasks gets the same clamp values of its parent however, when
the RESET_ON_FORK flag is set on parent, e.g. via:

   sys_sched_setattr()
      sched_setattr()
         __sched_setscheduler(attr::SCHED_FLAG_RESET_ON_FORK)

the new forked task is expected to start with all attributes reset to
default values.

Do that for utilization clamp values too by checking the reset request
from the existing uclamp_fork() call which already provides the required
initialization for other uclamp related bits.

Signed-off-by: Patrick Bellasi <patrick.bellasi@arm.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
---
 kernel/sched/core.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 7d4272440890..2c49b23efc87 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1071,6 +1071,14 @@ static void uclamp_fork(struct task_struct *p)
 
 	for_each_clamp_id(clamp_id)
 		p->uclamp[clamp_id].active = false;
+
+	if (likely(!p->sched_reset_on_fork))
+		return;
+
+	for_each_clamp_id(clamp_id) {
+		uclamp_se_set(&p->uclamp_req[clamp_id],
+			      uclamp_none(clamp_id), false);
+	}
 }
 
 static void __init init_uclamp(void)
-- 
2.21.0


^ permalink raw reply	[flat|nested] 27+ messages in thread

* [PATCH v10 08/16] sched/core: uclamp: Set default clamps for RT tasks
  2019-06-21  8:42 [PATCH v10 00/16] Add utilization clamping support Patrick Bellasi
                   ` (6 preceding siblings ...)
  2019-06-21  8:42 ` [PATCH v10 07/16] sched/core: uclamp: Reset uclamp values on RESET_ON_FORK Patrick Bellasi
@ 2019-06-21  8:42 ` Patrick Bellasi
  2019-06-21  8:42 ` [PATCH v10 09/16] sched/cpufreq: uclamp: Add clamps for FAIR and " Patrick Bellasi
                   ` (8 subsequent siblings)
  16 siblings, 0 replies; 27+ messages in thread
From: Patrick Bellasi @ 2019-06-21  8:42 UTC (permalink / raw)
  To: linux-kernel, linux-pm
  Cc: Ingo Molnar, Peter Zijlstra, Tejun Heo, Rafael J . Wysocki,
	Vincent Guittot, Viresh Kumar, Paul Turner, Quentin Perret,
	Dietmar Eggemann, Morten Rasmussen, Juri Lelli, Todd Kjos,
	Joel Fernandes, Steve Muckle, Suren Baghdasaryan,
	Alessio Balsini

By default FAIR tasks start without clamps, i.e. neither boosted nor
capped, and they run at the best frequency matching their utilization
demand.  This default behavior does not fit RT tasks which instead are
expected to run at the maximum available frequency, if not otherwise
required by explicitly capping them.

Enforce the correct behavior for RT tasks by setting util_min to max
whenever:

 1. the task is switched to the RT class and it does not already have a
    user-defined clamp value assigned.

 2. an RT task is forked from a parent with RESET_ON_FORK set.

NOTE: utilization clamp values are cross scheduling class attributes and
thus they are never changed/reset once a value has been explicitly
defined from user-space.

Signed-off-by: Patrick Bellasi <patrick.bellasi@arm.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
---
 kernel/sched/core.c | 30 ++++++++++++++++++++++++++++--
 1 file changed, 28 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 2c49b23efc87..ab75e874fdcc 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1051,6 +1051,27 @@ static int uclamp_validate(struct task_struct *p,
 static void __setscheduler_uclamp(struct task_struct *p,
 				  const struct sched_attr *attr)
 {
+	unsigned int clamp_id;
+
+	/*
+	 * On scheduling class change, reset to default clamps for tasks
+	 * without a task-specific value.
+	 */
+	for_each_clamp_id(clamp_id) {
+		struct uclamp_se *uc_se = &p->uclamp_req[clamp_id];
+		unsigned int clamp_value = uclamp_none(clamp_id);
+
+		/* Keep using defined clamps across class changes */
+		if (uc_se->user_defined)
+			continue;
+
+		/* By default, RT tasks always get 100% boost */
+		if (unlikely(rt_task(p) && clamp_id == UCLAMP_MIN))
+			clamp_value = uclamp_none(UCLAMP_MAX);
+
+		uclamp_se_set(uc_se, clamp_value, false);
+	}
+
 	if (likely(!(attr->sched_flags & SCHED_FLAG_UTIL_CLAMP)))
 		return;
 
@@ -1076,8 +1097,13 @@ static void uclamp_fork(struct task_struct *p)
 		return;
 
 	for_each_clamp_id(clamp_id) {
-		uclamp_se_set(&p->uclamp_req[clamp_id],
-			      uclamp_none(clamp_id), false);
+		unsigned int clamp_value = uclamp_none(clamp_id);
+
+		/* By default, RT tasks always get 100% boost */
+		if (unlikely(rt_task(p) && clamp_id == UCLAMP_MIN))
+			clamp_value = uclamp_none(UCLAMP_MAX);
+
+		uclamp_se_set(&p->uclamp_req[clamp_id], clamp_value, false);
 	}
 }
 
-- 
2.21.0


^ permalink raw reply	[flat|nested] 27+ messages in thread

* [PATCH v10 09/16] sched/cpufreq: uclamp: Add clamps for FAIR and RT tasks
  2019-06-21  8:42 [PATCH v10 00/16] Add utilization clamping support Patrick Bellasi
                   ` (7 preceding siblings ...)
  2019-06-21  8:42 ` [PATCH v10 08/16] sched/core: uclamp: Set default clamps for RT tasks Patrick Bellasi
@ 2019-06-21  8:42 ` " Patrick Bellasi
  2019-06-21  8:42 ` [PATCH v10 10/16] sched/core: uclamp: Add uclamp_util_with() Patrick Bellasi
                   ` (7 subsequent siblings)
  16 siblings, 0 replies; 27+ messages in thread
From: Patrick Bellasi @ 2019-06-21  8:42 UTC (permalink / raw)
  To: linux-kernel, linux-pm
  Cc: Ingo Molnar, Peter Zijlstra, Tejun Heo, Rafael J . Wysocki,
	Vincent Guittot, Viresh Kumar, Paul Turner, Quentin Perret,
	Dietmar Eggemann, Morten Rasmussen, Juri Lelli, Todd Kjos,
	Joel Fernandes, Steve Muckle, Suren Baghdasaryan,
	Alessio Balsini

Each time a frequency update is required via schedutil, a frequency is
selected to (possibly) satisfy the utilization reported by each
scheduling class and irqs. However, when utilization clamping is in use,
the frequency selection should consider userspace utilization clamping
hints.  This will allow, for example, to:

 - boost tasks which are directly affecting the user experience
   by running them at least at a minimum "requested" frequency

 - cap low priority tasks not directly affecting the user experience
   by running them only up to a maximum "allowed" frequency

These constraints are meant to support a per-task based tuning of the
frequency selection thus supporting a fine grained definition of
performance boosting vs energy saving strategies in kernel space.

Add support to clamp the utilization of RUNNABLE FAIR and RT tasks
within the boundaries defined by their aggregated utilization clamp
constraints.

Do that by considering the max(min_util, max_util) to give boosted tasks
the performance they need even when they happen to be co-scheduled with
other capped tasks.

Signed-off-by: Patrick Bellasi <patrick.bellasi@arm.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
---
 kernel/sched/cpufreq_schedutil.c | 15 ++++++++++++---
 kernel/sched/fair.c              |  4 ++++
 kernel/sched/rt.c                |  4 ++++
 kernel/sched/sched.h             | 23 +++++++++++++++++++++++
 4 files changed, 43 insertions(+), 3 deletions(-)

diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c
index 962cf343f798..35cdb4a4d802 100644
--- a/kernel/sched/cpufreq_schedutil.c
+++ b/kernel/sched/cpufreq_schedutil.c
@@ -202,8 +202,10 @@ unsigned long schedutil_freq_util(int cpu, unsigned long util_cfs,
 	unsigned long dl_util, util, irq;
 	struct rq *rq = cpu_rq(cpu);
 
-	if (type == FREQUENCY_UTIL && rt_rq_is_runnable(&rq->rt))
+	if (!IS_BUILTIN(CONFIG_UCLAMP_TASK) &&
+	    type == FREQUENCY_UTIL && rt_rq_is_runnable(&rq->rt)) {
 		return max;
+	}
 
 	/*
 	 * Early check to see if IRQ/steal time saturates the CPU, can be
@@ -219,9 +221,16 @@ unsigned long schedutil_freq_util(int cpu, unsigned long util_cfs,
 	 * CFS tasks and we use the same metric to track the effective
 	 * utilization (PELT windows are synchronized) we can directly add them
 	 * to obtain the CPU's actual utilization.
+	 *
+	 * CFS and RT utilization can be boosted or capped, depending on
+	 * utilization clamp constraints requested by currently RUNNABLE
+	 * tasks.
+	 * When there are no CFS RUNNABLE tasks, clamps are released and
+	 * frequency will be gracefully reduced with the utilization decay.
 	 */
-	util = util_cfs;
-	util += cpu_util_rt(rq);
+	util = util_cfs + cpu_util_rt(rq);
+	if (type == FREQUENCY_UTIL)
+		util = uclamp_util(rq, util);
 
 	dl_util = cpu_util_dl(rq);
 
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 3c11dcdedcbc..6de1547c2c13 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -10361,6 +10361,10 @@ 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 63ad7c90822c..a532558a5176 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -2400,6 +2400,10 @@ 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 cd36002436fc..c33a57f14743 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -2265,6 +2265,29 @@ static inline void cpufreq_update_util(struct rq *rq, unsigned int flags)
 static inline void cpufreq_update_util(struct rq *rq, unsigned int flags) {}
 #endif /* CONFIG_CPU_FREQ */
 
+#ifdef CONFIG_UCLAMP_TASK
+static inline unsigned int uclamp_util(struct rq *rq, unsigned int util)
+{
+	unsigned int min_util = READ_ONCE(rq->uclamp[UCLAMP_MIN].value);
+	unsigned int max_util = READ_ONCE(rq->uclamp[UCLAMP_MAX].value);
+
+	/*
+	 * Since CPU's {min,max}_util clamps are MAX aggregated considering
+	 * RUNNABLE tasks with _different_ clamps, we can end up with an
+	 * inversion. Fix it now when the clamps are applied.
+	 */
+	if (unlikely(min_util >= max_util))
+		return min_util;
+
+	return clamp(util, min_util, max_util);
+}
+#else /* CONFIG_UCLAMP_TASK */
+static inline unsigned int uclamp_util(struct rq *rq, unsigned int util)
+{
+	return util;
+}
+#endif /* CONFIG_UCLAMP_TASK */
+
 #ifdef arch_scale_freq_capacity
 # ifndef arch_scale_freq_invariant
 #  define arch_scale_freq_invariant()	true
-- 
2.21.0


^ permalink raw reply	[flat|nested] 27+ messages in thread

* [PATCH v10 10/16] sched/core: uclamp: Add uclamp_util_with()
  2019-06-21  8:42 [PATCH v10 00/16] Add utilization clamping support Patrick Bellasi
                   ` (8 preceding siblings ...)
  2019-06-21  8:42 ` [PATCH v10 09/16] sched/cpufreq: uclamp: Add clamps for FAIR and " Patrick Bellasi
@ 2019-06-21  8:42 ` Patrick Bellasi
  2019-06-21  8:42 ` [PATCH v10 11/16] sched/fair: uclamp: Add uclamp support to energy_compute() Patrick Bellasi
                   ` (6 subsequent siblings)
  16 siblings, 0 replies; 27+ messages in thread
From: Patrick Bellasi @ 2019-06-21  8:42 UTC (permalink / raw)
  To: linux-kernel, linux-pm
  Cc: Ingo Molnar, Peter Zijlstra, Tejun Heo, Rafael J . Wysocki,
	Vincent Guittot, Viresh Kumar, Paul Turner, Quentin Perret,
	Dietmar Eggemann, Morten Rasmussen, Juri Lelli, Todd Kjos,
	Joel Fernandes, Steve Muckle, Suren Baghdasaryan,
	Alessio Balsini

So far uclamp_util() allows to clamp a specified utilization considering
the clamp values requested by RUNNABLE tasks in a CPU. For the Energy
Aware Scheduler (EAS) it is interesting to test how clamp values will
change when a task is becoming RUNNABLE on a given CPU.
For example, EAS is interested in comparing the energy impact of
different scheduling decisions and the clamp values can play a role on
that.

Add uclamp_util_with() which allows to clamp a given utilization by
considering the possible impact on CPU clamp values of a specified task.

Signed-off-by: Patrick Bellasi <patrick.bellasi@arm.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
---
 kernel/sched/core.c  | 13 +++++++++++++
 kernel/sched/sched.h | 21 ++++++++++++++++++++-
 2 files changed, 33 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index ab75e874fdcc..2226ddd1de04 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -869,6 +869,19 @@ uclamp_eff_get(struct task_struct *p, unsigned int clamp_id)
 	return uc_req;
 }
 
+unsigned int uclamp_eff_value(struct task_struct *p, unsigned int clamp_id)
+{
+	struct uclamp_se uc_eff;
+
+	/* Task currently refcounted: use back-annotated (effective) value */
+	if (p->uclamp[clamp_id].active)
+		return p->uclamp[clamp_id].value;
+
+	uc_eff = uclamp_eff_get(p, clamp_id);
+
+	return uc_eff.value;
+}
+
 /*
  * When a task is enqueued on a rq, the clamp bucket currently defined by the
  * task's uclamp::bucket_id is refcounted on that rq. This also immediately
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index c33a57f14743..ce2da8b9ff8c 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -2266,11 +2266,20 @@ static inline void cpufreq_update_util(struct rq *rq, unsigned int flags) {}
 #endif /* CONFIG_CPU_FREQ */
 
 #ifdef CONFIG_UCLAMP_TASK
-static inline unsigned int uclamp_util(struct rq *rq, unsigned int util)
+unsigned int uclamp_eff_value(struct task_struct *p, unsigned int clamp_id);
+
+static __always_inline
+unsigned int uclamp_util_with(struct rq *rq, unsigned int util,
+			      struct task_struct *p)
 {
 	unsigned int min_util = READ_ONCE(rq->uclamp[UCLAMP_MIN].value);
 	unsigned int max_util = READ_ONCE(rq->uclamp[UCLAMP_MAX].value);
 
+	if (p) {
+		min_util = max(min_util, uclamp_eff_value(p, UCLAMP_MIN));
+		max_util = max(max_util, uclamp_eff_value(p, UCLAMP_MAX));
+	}
+
 	/*
 	 * Since CPU's {min,max}_util clamps are MAX aggregated considering
 	 * RUNNABLE tasks with _different_ clamps, we can end up with an
@@ -2281,7 +2290,17 @@ static inline unsigned int uclamp_util(struct rq *rq, unsigned int util)
 
 	return clamp(util, min_util, max_util);
 }
+
+static inline unsigned int uclamp_util(struct rq *rq, unsigned int util)
+{
+	return uclamp_util_with(rq, util, NULL);
+}
 #else /* CONFIG_UCLAMP_TASK */
+static inline unsigned int uclamp_util_with(struct rq *rq, unsigned int util,
+					    struct task_struct *p)
+{
+	return util;
+}
 static inline unsigned int uclamp_util(struct rq *rq, unsigned int util)
 {
 	return util;
-- 
2.21.0


^ permalink raw reply	[flat|nested] 27+ messages in thread

* [PATCH v10 11/16] sched/fair: uclamp: Add uclamp support to energy_compute()
  2019-06-21  8:42 [PATCH v10 00/16] Add utilization clamping support Patrick Bellasi
                   ` (9 preceding siblings ...)
  2019-06-21  8:42 ` [PATCH v10 10/16] sched/core: uclamp: Add uclamp_util_with() Patrick Bellasi
@ 2019-06-21  8:42 ` Patrick Bellasi
  2019-06-21 14:01   ` Peter Zijlstra
  2019-06-21  8:42 ` [PATCH v10 12/16] sched/core: uclamp: Extend CPU's cgroup controller Patrick Bellasi
                   ` (5 subsequent siblings)
  16 siblings, 1 reply; 27+ messages in thread
From: Patrick Bellasi @ 2019-06-21  8:42 UTC (permalink / raw)
  To: linux-kernel, linux-pm
  Cc: Ingo Molnar, Peter Zijlstra, Tejun Heo, Rafael J . Wysocki,
	Vincent Guittot, Viresh Kumar, Paul Turner, Quentin Perret,
	Dietmar Eggemann, Morten Rasmussen, Juri Lelli, Todd Kjos,
	Joel Fernandes, Steve Muckle, Suren Baghdasaryan,
	Alessio Balsini

The Energy Aware Scheduler (EAS) estimates the energy impact of waking
up a task on a given CPU. This estimation is based on:
 a) an (active) power consumption defined for each CPU frequency
 b) an estimation of which frequency will be used on each CPU
 c) an estimation of the busy time (utilization) of each CPU

Utilization clamping can affect both b) and c).
A CPU is expected to run:
 - on an higher than required frequency, but for a shorter time, in case
   its estimated utilization will be smaller than the minimum utilization
   enforced by uclamp
 - on a smaller than required frequency, but for a longer time, in case
   its estimated utilization is bigger than the maximum utilization
   enforced by uclamp

While compute_energy() already accounts clamping effects on busy time,
the clamping effects on frequency selection are currently ignored.

Fix it by considering how CPU clamp values will be affected by a
task waking up and being RUNNABLE on that CPU.

Do that by refactoring schedutil_freq_util() to take an additional
task_struct* which allows EAS to evaluate the impact on clamp values of
a task being eventually queued in a CPU. Clamp values are applied to the
RT+CFS utilization only when a FREQUENCY_UTIL is required by
compute_energy().

Do note that switching from ENERGY_UTIL to FREQUENCY_UTIL in the
computation of the cpu_util signal implies that we are more likely to
estimate the highest OPP when a RT task is running in another CPU of
the same performance domain. This can have an impact on energy
estimation but:
 - it's not easy to say which approach is better, since it depends on
   the use case
 - the original approach could still be obtained by setting a smaller
   task-specific util_min whenever required

Since we are at that:
 - rename schedutil_freq_util() into schedutil_cpu_util(),
   since it's not only used for frequency selection.

Signed-off-by: Patrick Bellasi <patrick.bellasi@arm.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
---
 kernel/sched/cpufreq_schedutil.c |  9 +++----
 kernel/sched/fair.c              | 40 +++++++++++++++++++++++++++-----
 kernel/sched/sched.h             | 20 +++++-----------
 3 files changed, 45 insertions(+), 24 deletions(-)

diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c
index 35cdb4a4d802..9c0419087260 100644
--- a/kernel/sched/cpufreq_schedutil.c
+++ b/kernel/sched/cpufreq_schedutil.c
@@ -196,8 +196,9 @@ static unsigned int get_next_freq(struct sugov_policy *sg_policy,
  * based on the task model parameters and gives the minimal utilization
  * required to meet deadlines.
  */
-unsigned long schedutil_freq_util(int cpu, unsigned long util_cfs,
-				  unsigned long max, enum schedutil_type type)
+unsigned long schedutil_cpu_util(int cpu, unsigned long util_cfs,
+				 unsigned long max, enum schedutil_type type,
+				 struct task_struct *p)
 {
 	unsigned long dl_util, util, irq;
 	struct rq *rq = cpu_rq(cpu);
@@ -230,7 +231,7 @@ unsigned long schedutil_freq_util(int cpu, unsigned long util_cfs,
 	 */
 	util = util_cfs + cpu_util_rt(rq);
 	if (type == FREQUENCY_UTIL)
-		util = uclamp_util(rq, util);
+		util = uclamp_util_with(rq, util, p);
 
 	dl_util = cpu_util_dl(rq);
 
@@ -290,7 +291,7 @@ static unsigned long sugov_get_util(struct sugov_cpu *sg_cpu)
 	sg_cpu->max = max;
 	sg_cpu->bw_dl = cpu_bw_dl(rq);
 
-	return schedutil_freq_util(sg_cpu->cpu, util, max, FREQUENCY_UTIL);
+	return schedutil_cpu_util(sg_cpu->cpu, util, max, FREQUENCY_UTIL, NULL);
 }
 
 /**
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 6de1547c2c13..964ebab863a6 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6203,11 +6203,21 @@ static unsigned long cpu_util_next(int cpu, struct task_struct *p, int dst_cpu)
 static long
 compute_energy(struct task_struct *p, int dst_cpu, struct perf_domain *pd)
 {
-	long util, max_util, sum_util, energy = 0;
+	unsigned int max_util, util_cfs, cpu_util, cpu_cap;
+	unsigned long sum_util, energy = 0;
+	struct task_struct *tsk;
 	int cpu;
 
 	for (; pd; pd = pd->next) {
+		struct cpumask *pd_mask = perf_domain_span(pd);
+
+		/*
+		 * The energy model mandates all the CPUs of a performance
+		 * domain have the same capacity.
+		 */
+		cpu_cap = arch_scale_cpu_capacity(NULL, cpumask_first(pd_mask));
 		max_util = sum_util = 0;
+
 		/*
 		 * The capacity state of CPUs of the current rd can be driven by
 		 * CPUs of another rd if they belong to the same performance
@@ -6218,11 +6228,29 @@ compute_energy(struct task_struct *p, int dst_cpu, struct perf_domain *pd)
 		 * it will not appear in its pd list and will not be accounted
 		 * by compute_energy().
 		 */
-		for_each_cpu_and(cpu, perf_domain_span(pd), cpu_online_mask) {
-			util = cpu_util_next(cpu, p, dst_cpu);
-			util = schedutil_energy_util(cpu, util);
-			max_util = max(util, max_util);
-			sum_util += util;
+		for_each_cpu_and(cpu, pd_mask, cpu_online_mask) {
+			util_cfs = cpu_util_next(cpu, p, dst_cpu);
+
+			/*
+			 * Busy time computation: utilization clamping is not
+			 * required since the ratio (sum_util / cpu_capacity)
+			 * is already enough to scale the EM reported power
+			 * consumption at the (eventually clamped) cpu_capacity.
+			 */
+			sum_util += schedutil_cpu_util(cpu, util_cfs, cpu_cap,
+						       ENERGY_UTIL, NULL);
+
+			/*
+			 * Performance domain frequency: utilization clamping
+			 * must be considered since it affects the selection
+			 * of the performance domain frequency.
+			 * NOTE: in case RT tasks are running, by default the
+			 * FREQUENCY_UTIL's utilization can be max OPP.
+			 */
+			tsk = cpu == dst_cpu ? p : NULL;
+			cpu_util = schedutil_cpu_util(cpu, util_cfs, cpu_cap,
+						      FREQUENCY_UTIL, tsk);
+			max_util = max(max_util, cpu_util);
 		}
 
 		energy += em_pd_energy(pd->em_pd, max_util, sum_util);
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index ce2da8b9ff8c..f81e8930ff19 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -2322,7 +2322,6 @@ static inline unsigned long capacity_orig_of(int cpu)
 }
 #endif
 
-#ifdef CONFIG_CPU_FREQ_GOV_SCHEDUTIL
 /**
  * enum schedutil_type - CPU utilization type
  * @FREQUENCY_UTIL:	Utilization used to select frequency
@@ -2338,15 +2337,11 @@ enum schedutil_type {
 	ENERGY_UTIL,
 };
 
-unsigned long schedutil_freq_util(int cpu, unsigned long util_cfs,
-				  unsigned long max, enum schedutil_type type);
-
-static inline unsigned long schedutil_energy_util(int cpu, unsigned long cfs)
-{
-	unsigned long max = arch_scale_cpu_capacity(NULL, cpu);
+#ifdef CONFIG_CPU_FREQ_GOV_SCHEDUTIL
 
-	return schedutil_freq_util(cpu, cfs, max, ENERGY_UTIL);
-}
+unsigned long schedutil_cpu_util(int cpu, unsigned long util_cfs,
+				 unsigned long max, enum schedutil_type type,
+				 struct task_struct *p);
 
 static inline unsigned long cpu_bw_dl(struct rq *rq)
 {
@@ -2375,11 +2370,8 @@ static inline unsigned long cpu_util_rt(struct rq *rq)
 	return READ_ONCE(rq->avg_rt.util_avg);
 }
 #else /* CONFIG_CPU_FREQ_GOV_SCHEDUTIL */
-static inline unsigned long schedutil_energy_util(int cpu, unsigned long cfs)
-{
-	return cfs;
-}
-#endif
+#define schedutil_cpu_util(cpu, util_cfs, max, type, p) 0
+#endif /* CONFIG_CPU_FREQ_GOV_SCHEDUTIL */
 
 #ifdef CONFIG_HAVE_SCHED_AVG_IRQ
 static inline unsigned long cpu_util_irq(struct rq *rq)
-- 
2.21.0


^ permalink raw reply	[flat|nested] 27+ messages in thread

* [PATCH v10 12/16] sched/core: uclamp: Extend CPU's cgroup controller
  2019-06-21  8:42 [PATCH v10 00/16] Add utilization clamping support Patrick Bellasi
                   ` (10 preceding siblings ...)
  2019-06-21  8:42 ` [PATCH v10 11/16] sched/fair: uclamp: Add uclamp support to energy_compute() Patrick Bellasi
@ 2019-06-21  8:42 ` Patrick Bellasi
  2019-06-22 15:03   ` Tejun Heo
  2019-06-21  8:42 ` [PATCH v10 13/16] sched/core: uclamp: Propagate parent clamps Patrick Bellasi
                   ` (4 subsequent siblings)
  16 siblings, 1 reply; 27+ messages in thread
From: Patrick Bellasi @ 2019-06-21  8:42 UTC (permalink / raw)
  To: linux-kernel, linux-pm
  Cc: Ingo Molnar, Peter Zijlstra, Tejun Heo, Rafael J . Wysocki,
	Vincent Guittot, Viresh Kumar, Paul Turner, Quentin Perret,
	Dietmar Eggemann, Morten Rasmussen, Juri Lelli, Todd Kjos,
	Joel Fernandes, Steve Muckle, Suren Baghdasaryan,
	Alessio Balsini

The cgroup CPU bandwidth controller allows to assign a specified
(maximum) bandwidth to the tasks of a group. However this bandwidth is
defined and enforced only on a temporal base, without considering the
actual frequency a CPU is running on. Thus, the amount of computation
completed by a task within an allocated bandwidth can be very different
depending on the actual frequency the CPU is running that task.
The amount of computation can be affected also by the specific CPU a
task is running on, especially when running on asymmetric capacity
systems like Arm's big.LITTLE.

With the availability of schedutil, the scheduler is now able
to drive frequency selections based on actual task utilization.
Moreover, the utilization clamping support provides a mechanism to
bias the frequency selection operated by schedutil depending on
constraints assigned to the tasks currently RUNNABLE on a CPU.

Giving the mechanisms described above, it is now possible to extend the
cpu controller to specify the minimum (or maximum) utilization which
should be considered for tasks RUNNABLE on a cpu.
This makes it possible to better defined the actual computational
power assigned to task groups, thus improving the cgroup CPU bandwidth
controller which is currently based just on time constraints.

Extend the CPU controller with a couple of new attributes uclamp.{min,max}
which allow to enforce utilization boosting and capping for all the
tasks in a group.

Specifically:

- uclamp.min: defines the minimum utilization which should be considered
	      i.e. the RUNNABLE tasks of this group will run at least at a
	      	 minimum frequency which corresponds to the uclamp.min
	      	 utilization

- uclamp.max: defines the maximum utilization which should be considered
	      i.e. the RUNNABLE tasks of this group will run up to a
	      	 maximum frequency which corresponds to the uclamp.max
	      	 utilization

These attributes:

a) are available only for non-root nodes, both on default and legacy
   hierarchies, while system wide clamps are defined by a generic
   interface which does not depends on cgroups. This system wide
   interface enforces constraints on tasks in the root node.

b) enforce effective constraints at each level of the hierarchy which
   are a restriction of the group requests considering its parent's
   effective constraints. Root group effective constraints are defined
   by the system wide interface.
   This mechanism allows each (non-root) level of the hierarchy to:
   - request whatever clamp values it would like to get
   - effectively get only up to the maximum amount allowed by its parent

c) have higher priority than task-specific clamps, defined via
   sched_setattr(), thus allowing to control and restrict task requests.

Add two new attributes to the cpu controller to collect "requested"
clamp values. Allow that at each non-root level of the hierarchy.
Validate local consistency by enforcing uclamp.min < uclamp.max.
Keep it simple by not caring now about "effective" values computation
and propagation along the hierarchy.

Signed-off-by: Patrick Bellasi <patrick.bellasi@arm.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Tejun Heo <tj@kernel.org>

---
Changes in v10:
 Message-ID: <https://lore.kernel.org/lkml/20190603122422.GA19426@darkstar/>
 - rename cgroup attributes to be cpu.uclamp.{min,max}
 Message-ID: <https://lore.kernel.org/lkml/20190605152754.GO374014@devbig004.ftw2.facebook.com/>
 - use a percentage rational numbers for clamp attributes
 Message-ID: <https://lore.kernel.org/lkml/20190605153955.GP374014@devbig004.ftw2.facebook.com/>
 - update initialization of subgroups clamps to be none by default
---
 Documentation/admin-guide/cgroup-v2.rst |  29 ++++
 init/Kconfig                            |  22 +++
 kernel/sched/core.c                     | 181 +++++++++++++++++++++++-
 kernel/sched/sched.h                    |   6 +
 4 files changed, 237 insertions(+), 1 deletion(-)

diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst
index a5c845338d6d..4761d20c5cad 100644
--- a/Documentation/admin-guide/cgroup-v2.rst
+++ b/Documentation/admin-guide/cgroup-v2.rst
@@ -951,6 +951,12 @@ controller implements weight and absolute bandwidth limit models for
 normal scheduling policy and absolute bandwidth allocation model for
 realtime scheduling policy.
 
+Cycles distribution is based, by default, on a temporal base and it
+does not account for the frequency at which tasks are executed.
+The (optional) utilization clamping support allows to enforce a minimum
+bandwidth, which should always be provided by a CPU, and a maximum bandwidth,
+which should never be exceeded by a CPU.
+
 WARNING: cgroup2 doesn't yet support control of realtime processes and
 the cpu controller can only be enabled when all RT processes are in
 the root cgroup.  Be aware that system management software may already
@@ -1016,6 +1022,29 @@ All time durations are in microseconds.
 	Shows pressure stall information for CPU. See
 	Documentation/accounting/psi.txt for details.
 
+  cpu.uclamp.min
+        A read-write single value file which exists on non-root cgroups.
+        The default is "0", i.e. no utilization boosting.
+
+        The requested minimum utilization as a percentage rational number,
+        e.g. 12.34 for 12.34%.
+
+        This interface allows reading and setting minimum utilization clamp
+        values similar to the sched_setattr(2). This minimum utilization
+        value is used to clamp the task specific minimum utilization clamp.
+
+  cpu.uclamp.max
+        A read-write single value file which exists on non-root cgroups.
+        The default is "max". i.e. no utilization capping
+
+        The requested maximum utilization as a percentage rational number,
+        e.g. 98.76 for 98.76%.
+
+        This interface allows reading and setting maximum utilization clamp
+        values similar to the sched_setattr(2). This maximum utilization
+        value is used to clamp the task specific maximum utilization clamp.
+
+
 
 Memory
 ------
diff --git a/init/Kconfig b/init/Kconfig
index bf96faf3fe43..68a21188786c 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -903,6 +903,28 @@ config RT_GROUP_SCHED
 
 endif #CGROUP_SCHED
 
+config UCLAMP_TASK_GROUP
+	bool "Utilization clamping per group of tasks"
+	depends on CGROUP_SCHED
+	depends on UCLAMP_TASK
+	default n
+	help
+	  This feature enables the scheduler to track the clamped utilization
+	  of each CPU based on RUNNABLE tasks currently scheduled on that CPU.
+
+	  When this option is enabled, the user can specify a min and max
+	  CPU bandwidth which is allowed for each single task in a group.
+	  The max bandwidth allows to clamp the maximum frequency a task
+	  can use, while the min bandwidth allows to define a minimum
+	  frequency a task will always use.
+
+	  When task group based utilization clamping is enabled, an eventually
+	  specified task-specific clamp value is constrained by the cgroup
+	  specified clamp value. Both minimum and maximum task clamping cannot
+	  be bigger than the corresponding clamping defined at task group level.
+
+	  If in doubt, say N.
+
 config CGROUP_PIDS
 	bool "PIDs controller"
 	help
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 2226ddd1de04..0975f832066e 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1138,8 +1138,12 @@ static void __init init_uclamp(void)
 
 	/* System defaults allow max clamp values for both indexes */
 	uclamp_se_set(&uc_max, uclamp_none(UCLAMP_MAX), false);
-	for_each_clamp_id(clamp_id)
+	for_each_clamp_id(clamp_id) {
 		uclamp_default[clamp_id] = uc_max;
+#ifdef CONFIG_UCLAMP_TASK_GROUP
+		root_task_group.uclamp_req[clamp_id] = uc_max;
+#endif
+	}
 }
 
 #else /* CONFIG_UCLAMP_TASK */
@@ -6714,6 +6718,19 @@ void ia64_set_curr_task(int cpu, struct task_struct *p)
 /* task_group_lock serializes the addition/removal of task groups */
 static DEFINE_SPINLOCK(task_group_lock);
 
+static inline void alloc_uclamp_sched_group(struct task_group *tg,
+					    struct task_group *parent)
+{
+#ifdef CONFIG_UCLAMP_TASK_GROUP
+	int clamp_id;
+
+	for_each_clamp_id(clamp_id) {
+		uclamp_se_set(&tg->uclamp_req[clamp_id],
+			      uclamp_none(clamp_id), false);
+	}
+#endif
+}
+
 static void sched_free_group(struct task_group *tg)
 {
 	free_fair_sched_group(tg);
@@ -6737,6 +6754,8 @@ struct task_group *sched_create_group(struct task_group *parent)
 	if (!alloc_rt_sched_group(tg, parent))
 		goto err;
 
+	alloc_uclamp_sched_group(tg, parent);
+
 	return tg;
 
 err:
@@ -6957,6 +6976,138 @@ static void cpu_cgroup_attach(struct cgroup_taskset *tset)
 		sched_move_task(task);
 }
 
+#ifdef CONFIG_UCLAMP_TASK_GROUP
+static inline int uclamp_scale_from_percent(char *buf, u64 *value)
+{
+	*value = SCHED_CAPACITY_SCALE;
+
+	buf = strim(buf);
+	if (strncmp("max", buf, 4)) {
+		s64 percent;
+		int ret;
+
+		ret = cgroup_parse_float(buf, 2, &percent);
+		if (ret)
+			return ret;
+
+		percent <<= SCHED_CAPACITY_SHIFT;
+		*value = DIV_ROUND_CLOSEST_ULL(percent, 10000);
+	}
+
+	return 0;
+}
+
+static inline u64 uclamp_percent_from_scale(u64 value)
+{
+	return DIV_ROUND_CLOSEST_ULL(value * 10000, SCHED_CAPACITY_SCALE);
+}
+
+static ssize_t cpu_uclamp_min_write(struct kernfs_open_file *of,
+				    char *buf, size_t nbytes,
+				    loff_t off)
+{
+	struct task_group *tg;
+	u64 min_value;
+	int ret;
+
+	ret = uclamp_scale_from_percent(buf, &min_value);
+	if (ret)
+		return ret;
+	if (min_value > SCHED_CAPACITY_SCALE)
+		return -ERANGE;
+
+	rcu_read_lock();
+
+	tg = css_tg(of_css(of));
+	if (tg == &root_task_group) {
+		ret = -EINVAL;
+		goto out;
+	}
+	if (tg->uclamp_req[UCLAMP_MIN].value == min_value)
+		goto out;
+	if (tg->uclamp_req[UCLAMP_MAX].value < min_value) {
+		ret = -EINVAL;
+		goto out;
+	}
+
+	uclamp_se_set(&tg->uclamp_req[UCLAMP_MIN], min_value, false);
+
+out:
+	rcu_read_unlock();
+
+	return nbytes;
+}
+
+static ssize_t cpu_uclamp_max_write(struct kernfs_open_file *of,
+				    char *buf, size_t nbytes,
+				    loff_t off)
+{
+	struct task_group *tg;
+	u64 max_value;
+	int ret;
+
+	ret = uclamp_scale_from_percent(buf, &max_value);
+	if (ret)
+		return ret;
+	if (max_value > SCHED_CAPACITY_SCALE)
+		return -ERANGE;
+
+	rcu_read_lock();
+
+	tg = css_tg(of_css(of));
+	if (tg == &root_task_group) {
+		ret = -EINVAL;
+		goto out;
+	}
+	if (tg->uclamp_req[UCLAMP_MAX].value == max_value)
+		goto out;
+	if (tg->uclamp_req[UCLAMP_MIN].value > max_value) {
+		ret = -EINVAL;
+		goto out;
+	}
+
+	uclamp_se_set(&tg->uclamp_req[UCLAMP_MAX], max_value, false);
+
+out:
+	rcu_read_unlock();
+
+	return nbytes;
+}
+
+static inline void cpu_uclamp_print(struct seq_file *sf,
+				    enum uclamp_id clamp_id)
+{
+	struct task_group *tg;
+	u64 util_clamp;
+	u64 percent;
+
+	rcu_read_lock();
+	tg = css_tg(seq_css(sf));
+	util_clamp = tg->uclamp_req[clamp_id].value;
+	rcu_read_unlock();
+
+	if (util_clamp == SCHED_CAPACITY_SCALE) {
+		seq_puts(sf, "max\n");
+		return;
+	}
+
+	percent = uclamp_percent_from_scale(util_clamp);
+	seq_printf(sf, "%llu.%llu\n", percent / 100, percent % 100);
+}
+
+static int cpu_uclamp_min_show(struct seq_file *sf, void *v)
+{
+	cpu_uclamp_print(sf, UCLAMP_MIN);
+	return 0;
+}
+
+static int cpu_uclamp_max_show(struct seq_file *sf, void *v)
+{
+	cpu_uclamp_print(sf, UCLAMP_MAX);
+	return 0;
+}
+#endif /* CONFIG_UCLAMP_TASK_GROUP */
+
 #ifdef CONFIG_FAIR_GROUP_SCHED
 static int cpu_shares_write_u64(struct cgroup_subsys_state *css,
 				struct cftype *cftype, u64 shareval)
@@ -7301,6 +7452,20 @@ static struct cftype cpu_legacy_files[] = {
 		.read_u64 = cpu_rt_period_read_uint,
 		.write_u64 = cpu_rt_period_write_uint,
 	},
+#endif
+#ifdef CONFIG_UCLAMP_TASK_GROUP
+	{
+		.name = "uclamp.min",
+		.flags = CFTYPE_NOT_ON_ROOT,
+		.seq_show = cpu_uclamp_min_show,
+		.write = cpu_uclamp_min_write,
+	},
+	{
+		.name = "uclamp.max",
+		.flags = CFTYPE_NOT_ON_ROOT,
+		.seq_show = cpu_uclamp_max_show,
+		.write = cpu_uclamp_max_write,
+	},
 #endif
 	{ }	/* Terminate */
 };
@@ -7468,6 +7633,20 @@ static struct cftype cpu_files[] = {
 		.seq_show = cpu_max_show,
 		.write = cpu_max_write,
 	},
+#endif
+#ifdef CONFIG_UCLAMP_TASK_GROUP
+	{
+		.name = "uclamp.min",
+		.flags = CFTYPE_NOT_ON_ROOT,
+		.seq_show = cpu_uclamp_min_show,
+		.write = cpu_uclamp_min_write,
+	},
+	{
+		.name = "uclamp.max",
+		.flags = CFTYPE_NOT_ON_ROOT,
+		.seq_show = cpu_uclamp_max_show,
+		.write = cpu_uclamp_max_write,
+	},
 #endif
 	{ }	/* terminate */
 };
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index f81e8930ff19..bdbefd50ff46 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -393,6 +393,12 @@ struct task_group {
 #endif
 
 	struct cfs_bandwidth	cfs_bandwidth;
+
+#ifdef CONFIG_UCLAMP_TASK_GROUP
+	/* Clamp values requested for a task group */
+	struct uclamp_se	uclamp_req[UCLAMP_CNT];
+#endif
+
 };
 
 #ifdef CONFIG_FAIR_GROUP_SCHED
-- 
2.21.0


^ permalink raw reply	[flat|nested] 27+ messages in thread

* [PATCH v10 13/16] sched/core: uclamp: Propagate parent clamps
  2019-06-21  8:42 [PATCH v10 00/16] Add utilization clamping support Patrick Bellasi
                   ` (11 preceding siblings ...)
  2019-06-21  8:42 ` [PATCH v10 12/16] sched/core: uclamp: Extend CPU's cgroup controller Patrick Bellasi
@ 2019-06-21  8:42 ` Patrick Bellasi
  2019-06-22 15:07   ` Tejun Heo
  2019-06-21  8:42 ` [PATCH v10 14/16] sched/core: uclamp: Propagate system defaults to root group Patrick Bellasi
                   ` (3 subsequent siblings)
  16 siblings, 1 reply; 27+ messages in thread
From: Patrick Bellasi @ 2019-06-21  8:42 UTC (permalink / raw)
  To: linux-kernel, linux-pm
  Cc: Ingo Molnar, Peter Zijlstra, Tejun Heo, Rafael J . Wysocki,
	Vincent Guittot, Viresh Kumar, Paul Turner, Quentin Perret,
	Dietmar Eggemann, Morten Rasmussen, Juri Lelli, Todd Kjos,
	Joel Fernandes, Steve Muckle, Suren Baghdasaryan,
	Alessio Balsini

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 is the actual clamp value enforced on tasks in a
task group.

Since it can be interesting for userspace, e.g. system management
software, to know exactly what the currently propagated/enforced
configuration is, 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@arm.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Tejun Heo <tj@kernel.org>

---
Changes in v10:
 Message-ID: <https://lore.kernel.org/lkml/20190603122422.GA19426@darkstar/>
 - rename cgroup attributes to be cpu.uclamp.{min,max}
 Message-ID: <https://lore.kernel.org/lkml/20190605152754.GO374014@devbig004.ftw2.facebook.com/>
 - use a percentage rational numbers for clamp attributes
---
 Documentation/admin-guide/cgroup-v2.rst |  21 +++++
 kernel/sched/core.c                     | 103 +++++++++++++++++++++++-
 kernel/sched/sched.h                    |   2 +
 3 files changed, 122 insertions(+), 4 deletions(-)

diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst
index 4761d20c5cad..d4407c40bc64 100644
--- a/Documentation/admin-guide/cgroup-v2.rst
+++ b/Documentation/admin-guide/cgroup-v2.rst
@@ -1033,6 +1033,17 @@ All time durations are in microseconds.
         values similar to the sched_setattr(2). This minimum utilization
         value is used to clamp the task specific minimum utilization clamp.
 
+  cpu.uclamp.min.effective
+        A read-only single value file which exists on non-root cgroups and
+        reports minimum utilization clamp value currently enforced on a task
+        group.
+
+        The actual minimum utilization as a percentage rational number,
+        e.g. 12.34 for 12.34%.
+
+        This value can be lower then cpu.uclamp.min in case a parent cgroup
+        allows only smaller minimum utilization values.
+
   cpu.uclamp.max
         A read-write single value file which exists on non-root cgroups.
         The default is "max". i.e. no utilization capping
@@ -1044,6 +1055,16 @@ All time durations are in microseconds.
         values similar to the sched_setattr(2). This maximum utilization
         value is used to clamp the task specific maximum utilization clamp.
 
+  cpu.uclamp.max.effective
+        A read-only single value file which exists on non-root cgroups and
+        reports maximum utilization clamp value currently enforced on a task
+        group.
+
+        The actual maximum utilization as a percentage rational number,
+        e.g. 98.76 for 98.76%.
+
+        This value can be lower then cpu.uclamp.max in case a parent cgroup
+        is enforcing a more restrictive clamping on max utilization.
 
 
 Memory
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 0975f832066e..2b4d0b9bd6b9 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -762,6 +762,18 @@ static void set_load_weight(struct task_struct *p, bool update_load)
 }
 
 #ifdef CONFIG_UCLAMP_TASK
+/*
+ * Serializes updates of utilization clamp values
+ *
+ * The (slow-path) user-space triggers utilization clamp value updates which
+ * can require updates on (fast-path) scheduler's data structures used to
+ * support enqueue/dequeue operations.
+ * While the per-CPU rq lock protects fast-path update operations, user-space
+ * requests are serialized using a mutex to reduce the risk of conflicting
+ * updates or API abuses.
+ */
+static DEFINE_MUTEX(uclamp_mutex);
+
 /* Max allowed minimum utilization */
 unsigned int sysctl_sched_uclamp_util_min = SCHED_CAPACITY_SCALE;
 
@@ -1126,6 +1138,8 @@ static void __init init_uclamp(void)
 	unsigned int clamp_id;
 	int cpu;
 
+	mutex_init(&uclamp_mutex);
+
 	for_each_possible_cpu(cpu) {
 		memset(&cpu_rq(cpu)->uclamp, 0, sizeof(struct uclamp_rq));
 		cpu_rq(cpu)->uclamp_flags = 0;
@@ -1142,6 +1156,7 @@ static void __init init_uclamp(void)
 		uclamp_default[clamp_id] = uc_max;
 #ifdef CONFIG_UCLAMP_TASK_GROUP
 		root_task_group.uclamp_req[clamp_id] = uc_max;
+		root_task_group.uclamp[clamp_id] = uc_max;
 #endif
 	}
 }
@@ -6727,6 +6742,7 @@ static inline void alloc_uclamp_sched_group(struct task_group *tg,
 	for_each_clamp_id(clamp_id) {
 		uclamp_se_set(&tg->uclamp_req[clamp_id],
 			      uclamp_none(clamp_id), false);
+		tg->uclamp[clamp_id] = parent->uclamp[clamp_id];
 	}
 #endif
 }
@@ -6977,6 +6993,44 @@ static void cpu_cgroup_attach(struct cgroup_taskset *tset)
 }
 
 #ifdef CONFIG_UCLAMP_TASK_GROUP
+static void cpu_util_update_eff(struct cgroup_subsys_state *css,
+				unsigned int clamp_id)
+{
+	struct cgroup_subsys_state *top_css = css;
+	struct uclamp_se *uc_se, *uc_parent;
+	unsigned int value;
+
+	css_for_each_descendant_pre(css, top_css) {
+		value = css_tg(css)->uclamp_req[clamp_id].value;
+
+		uc_parent = NULL;
+		if (css_tg(css)->parent)
+			uc_parent = &css_tg(css)->parent->uclamp[clamp_id];
+
+		/*
+		 * Skip the whole subtrees if the current effective clamp is
+		 * already matching the TG's clamp value.
+		 * In this case, all the subtrees already have top_value, or a
+		 * more restrictive value, as effective clamp.
+		 */
+		uc_se = &css_tg(css)->uclamp[clamp_id];
+		if (uc_se->value == value &&
+		    uc_parent && uc_parent->value >= value) {
+			css = css_rightmost_descendant(css);
+			continue;
+		}
+
+		/* Propagate the most restrictive effective value */
+		if (uc_parent && uc_parent->value < value)
+			value = uc_parent->value;
+		if (uc_se->value == value)
+			continue;
+
+		uc_se->value = value;
+		uc_se->bucket_id = uclamp_bucket_id(value);
+	}
+}
+
 static inline int uclamp_scale_from_percent(char *buf, u64 *value)
 {
 	*value = SCHED_CAPACITY_SCALE;
@@ -7016,6 +7070,7 @@ static ssize_t cpu_uclamp_min_write(struct kernfs_open_file *of,
 	if (min_value > SCHED_CAPACITY_SCALE)
 		return -ERANGE;
 
+	mutex_lock(&uclamp_mutex);
 	rcu_read_lock();
 
 	tg = css_tg(of_css(of));
@@ -7032,8 +7087,12 @@ static ssize_t cpu_uclamp_min_write(struct kernfs_open_file *of,
 
 	uclamp_se_set(&tg->uclamp_req[UCLAMP_MIN], min_value, false);
 
+	/* Update effective clamps to track the most restrictive value */
+	cpu_util_update_eff(of_css(of), UCLAMP_MIN);
+
 out:
 	rcu_read_unlock();
+	mutex_unlock(&uclamp_mutex);
 
 	return nbytes;
 }
@@ -7052,6 +7111,7 @@ static ssize_t cpu_uclamp_max_write(struct kernfs_open_file *of,
 	if (max_value > SCHED_CAPACITY_SCALE)
 		return -ERANGE;
 
+	mutex_lock(&uclamp_mutex);
 	rcu_read_lock();
 
 	tg = css_tg(of_css(of));
@@ -7068,14 +7128,19 @@ static ssize_t cpu_uclamp_max_write(struct kernfs_open_file *of,
 
 	uclamp_se_set(&tg->uclamp_req[UCLAMP_MAX], max_value, false);
 
+	/* Update effective clamps to track the most restrictive value */
+	cpu_util_update_eff(of_css(of), UCLAMP_MAX);
+
 out:
 	rcu_read_unlock();
+	mutex_unlock(&uclamp_mutex);
 
 	return nbytes;
 }
 
 static inline void cpu_uclamp_print(struct seq_file *sf,
-				    enum uclamp_id clamp_id)
+				    enum uclamp_id clamp_id,
+				    bool effective)
 {
 	struct task_group *tg;
 	u64 util_clamp;
@@ -7083,7 +7148,9 @@ static inline void cpu_uclamp_print(struct seq_file *sf,
 
 	rcu_read_lock();
 	tg = css_tg(seq_css(sf));
-	util_clamp = tg->uclamp_req[clamp_id].value;
+	util_clamp = effective
+		? tg->uclamp[clamp_id].value
+		: tg->uclamp_req[clamp_id].value;
 	rcu_read_unlock();
 
 	if (util_clamp == SCHED_CAPACITY_SCALE) {
@@ -7097,13 +7164,25 @@ static inline void cpu_uclamp_print(struct seq_file *sf,
 
 static int cpu_uclamp_min_show(struct seq_file *sf, void *v)
 {
-	cpu_uclamp_print(sf, UCLAMP_MIN);
+	cpu_uclamp_print(sf, UCLAMP_MIN, false);
 	return 0;
 }
 
 static int cpu_uclamp_max_show(struct seq_file *sf, void *v)
 {
-	cpu_uclamp_print(sf, UCLAMP_MAX);
+	cpu_uclamp_print(sf, UCLAMP_MAX, false);
+	return 0;
+}
+
+static int cpu_uclamp_min_effective_show(struct seq_file *sf, void *v)
+{
+	cpu_uclamp_print(sf, UCLAMP_MIN, true);
+	return 0;
+}
+
+static int cpu_uclamp_max_effective_show(struct seq_file *sf, void *v)
+{
+	cpu_uclamp_print(sf, UCLAMP_MAX, true);
 	return 0;
 }
 #endif /* CONFIG_UCLAMP_TASK_GROUP */
@@ -7460,12 +7539,20 @@ static struct cftype cpu_legacy_files[] = {
 		.seq_show = cpu_uclamp_min_show,
 		.write = cpu_uclamp_min_write,
 	},
+	{
+		.name = "uclamp.min.effective",
+		.seq_show = cpu_uclamp_min_effective_show,
+	},
 	{
 		.name = "uclamp.max",
 		.flags = CFTYPE_NOT_ON_ROOT,
 		.seq_show = cpu_uclamp_max_show,
 		.write = cpu_uclamp_max_write,
 	},
+	{
+		.name = "uclamp.max.effective",
+		.seq_show = cpu_uclamp_max_effective_show,
+	},
 #endif
 	{ }	/* Terminate */
 };
@@ -7641,12 +7728,20 @@ static struct cftype cpu_files[] = {
 		.seq_show = cpu_uclamp_min_show,
 		.write = cpu_uclamp_min_write,
 	},
+	{
+		.name = "uclamp.min.effective",
+		.seq_show = cpu_uclamp_min_effective_show,
+	},
 	{
 		.name = "uclamp.max",
 		.flags = CFTYPE_NOT_ON_ROOT,
 		.seq_show = cpu_uclamp_max_show,
 		.write = cpu_uclamp_max_write,
 	},
+	{
+		.name = "uclamp.max.effective",
+		.seq_show = cpu_uclamp_max_effective_show,
+	},
 #endif
 	{ }	/* terminate */
 };
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index bdbefd50ff46..507c99898a2a 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -397,6 +397,8 @@ struct task_group {
 #ifdef CONFIG_UCLAMP_TASK_GROUP
 	/* Clamp values requested for a task group */
 	struct uclamp_se	uclamp_req[UCLAMP_CNT];
+	/* Effective clamp values used for a task group */
+	struct uclamp_se	uclamp[UCLAMP_CNT];
 #endif
 
 };
-- 
2.21.0


^ permalink raw reply	[flat|nested] 27+ messages in thread

* [PATCH v10 14/16] sched/core: uclamp: Propagate system defaults to root group
  2019-06-21  8:42 [PATCH v10 00/16] Add utilization clamping support Patrick Bellasi
                   ` (12 preceding siblings ...)
  2019-06-21  8:42 ` [PATCH v10 13/16] sched/core: uclamp: Propagate parent clamps Patrick Bellasi
@ 2019-06-21  8:42 ` Patrick Bellasi
  2019-06-21  8:42 ` [PATCH v10 15/16] sched/core: uclamp: Use TG's clamps to restrict TASK's clamps Patrick Bellasi
                   ` (2 subsequent siblings)
  16 siblings, 0 replies; 27+ messages in thread
From: Patrick Bellasi @ 2019-06-21  8:42 UTC (permalink / raw)
  To: linux-kernel, linux-pm
  Cc: Ingo Molnar, Peter Zijlstra, Tejun Heo, Rafael J . Wysocki,
	Vincent Guittot, Viresh Kumar, Paul Turner, Quentin Perret,
	Dietmar Eggemann, Morten Rasmussen, Juri Lelli, Todd Kjos,
	Joel Fernandes, Steve Muckle, Suren Baghdasaryan,
	Alessio Balsini

The clamp values are not tunable at the level of the root task group.
That's for two main reasons:

 - the root group represents "system resources" which are always
   entirely available from the cgroup standpoint.

 - when tuning/restricting "system resources" makes sense, tuning must
   be done using a system wide API which should also be available when
   control groups are not.

When a system wide restriction is available, cgroups should be aware of
its value in order to know exactly how much "system resources" are
available for the subgroups.

Utilization clamping supports already the concepts of:

 - system defaults: which define the maximum possible clamp values
   usable by tasks.

 - effective clamps: which allows a parent cgroup to constraint (maybe
   temporarily) its descendants without losing the information related
   to the values "requested" from them.

Exploit these two concepts and bind them together in such a way that,
whenever system default are tuned, the new values are propagated to
(possibly) restrict or relax the "effective" value of nested cgroups.

Signed-off-by: Patrick Bellasi <patrick.bellasi@arm.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Tejun Heo <tj@kernel.org>
---
 kernel/sched/core.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 2b4d0b9bd6b9..f09712f65017 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1006,6 +1006,13 @@ static inline void uclamp_rq_dec(struct rq *rq, struct task_struct *p)
 		uclamp_rq_dec_id(rq, p, clamp_id);
 }
 
+#ifdef CONFIG_UCLAMP_TASK_GROUP
+static void cpu_util_update_eff(struct cgroup_subsys_state *css,
+				unsigned int clamp_id);
+#else
+#define cpu_util_update_eff(...)
+#endif
+
 int sysctl_sched_uclamp_handler(struct ctl_table *table, int write,
 				void __user *buffer, size_t *lenp,
 				loff_t *ppos)
@@ -1039,6 +1046,9 @@ int sysctl_sched_uclamp_handler(struct ctl_table *table, int write,
 			      sysctl_sched_uclamp_util_max, false);
 	}
 
+	cpu_util_update_eff(&root_task_group.css, UCLAMP_MIN);
+	cpu_util_update_eff(&root_task_group.css, UCLAMP_MAX);
+
 	/*
 	 * Updating all the RUNNABLE task is expensive, keep it simple and do
 	 * just a lazy update at each next enqueue time.
-- 
2.21.0


^ permalink raw reply	[flat|nested] 27+ messages in thread

* [PATCH v10 15/16] sched/core: uclamp: Use TG's clamps to restrict TASK's clamps
  2019-06-21  8:42 [PATCH v10 00/16] Add utilization clamping support Patrick Bellasi
                   ` (13 preceding siblings ...)
  2019-06-21  8:42 ` [PATCH v10 14/16] sched/core: uclamp: Propagate system defaults to root group Patrick Bellasi
@ 2019-06-21  8:42 ` Patrick Bellasi
  2019-06-21  8:42 ` [PATCH v10 16/16] sched/core: uclamp: Update CPU's refcount on TG's clamp changes Patrick Bellasi
  2019-06-21 14:55 ` [PATCH v10 00/16] Add utilization clamping support Patrick Bellasi
  16 siblings, 0 replies; 27+ messages in thread
From: Patrick Bellasi @ 2019-06-21  8:42 UTC (permalink / raw)
  To: linux-kernel, linux-pm
  Cc: Ingo Molnar, Peter Zijlstra, Tejun Heo, Rafael J . Wysocki,
	Vincent Guittot, Viresh Kumar, Paul Turner, Quentin Perret,
	Dietmar Eggemann, Morten Rasmussen, Juri Lelli, Todd Kjos,
	Joel Fernandes, Steve Muckle, Suren Baghdasaryan,
	Alessio Balsini

When a task specific clamp value is configured via sched_setattr(2),
this value is accounted in the corresponding clamp bucket every time the
task is {en,de}qeued. However, when cgroups are also in use, the task
specific clamp values could be restricted by the task_group (TG)
clamp values.

Update uclamp_cpu_inc() to aggregate task and TG clamp values. Every
time a task is enqueued, it's accounted in the clamp_bucket defining the
smaller clamp between the task specific value and its TG effective
value. This allows to:

1. ensure cgroup clamps are always used to restrict task specific
   requests, i.e. boosted only up to the effective granted value or
   clamped at least to a certain value

2. implement a "nice-like" policy, where tasks are still allowed to
   request less then what enforced by their current TG

This mimics what already happens for a task's CPU affinity mask when the
task is also in a cpuset, i.e. cgroup attributes are always used to
restrict per-task attributes.

Do this by exploiting the concept of "effective" clamp, which is already
used by a TG to track parent enforced restrictions.

Apply task group clamp restrictions only to tasks belonging to a child
group. While, for tasks in the root group or in an autogroup, only
system defaults are enforced.

Signed-off-by: Patrick Bellasi <patrick.bellasi@arm.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Tejun Heo <tj@kernel.org>
---
 kernel/sched/core.c | 28 +++++++++++++++++++++++++++-
 1 file changed, 27 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index f09712f65017..8070e11cafa0 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -862,16 +862,42 @@ unsigned int uclamp_rq_max_value(struct rq *rq, unsigned int clamp_id,
 	return uclamp_idle_value(rq, clamp_id, clamp_value);
 }
 
+static inline struct uclamp_se
+uclamp_tg_restrict(struct task_struct *p, unsigned int clamp_id)
+{
+	struct uclamp_se uc_req = p->uclamp_req[clamp_id];
+#ifdef CONFIG_UCLAMP_TASK_GROUP
+	struct uclamp_se uc_max;
+
+	/*
+	 * Tasks in autogroups or root task group will be
+	 * restricted by system defaults.
+	 */
+	if (task_group_is_autogroup(task_group(p)))
+		return uc_req;
+	if (task_group(p) == &root_task_group)
+		return uc_req;
+
+	uc_max = task_group(p)->uclamp[clamp_id];
+	if (uc_req.value > uc_max.value || !uc_req.user_defined)
+		return uc_max;
+#endif
+
+	return uc_req;
+}
+
 /*
  * The effective clamp bucket index of a task depends on, by increasing
  * priority:
  * - the task specific clamp value, when explicitly requested from userspace
+ * - the task group effective clamp value, for tasks not either in the root
+ *   group or in an autogroup
  * - the system default clamp value, defined by the sysadmin
  */
 static inline struct uclamp_se
 uclamp_eff_get(struct task_struct *p, unsigned int clamp_id)
 {
-	struct uclamp_se uc_req = p->uclamp_req[clamp_id];
+	struct uclamp_se uc_req = uclamp_tg_restrict(p, clamp_id);
 	struct uclamp_se uc_max = uclamp_default[clamp_id];
 
 	/* System default restrictions always apply */
-- 
2.21.0


^ permalink raw reply	[flat|nested] 27+ messages in thread

* [PATCH v10 16/16] sched/core: uclamp: Update CPU's refcount on TG's clamp changes
  2019-06-21  8:42 [PATCH v10 00/16] Add utilization clamping support Patrick Bellasi
                   ` (14 preceding siblings ...)
  2019-06-21  8:42 ` [PATCH v10 15/16] sched/core: uclamp: Use TG's clamps to restrict TASK's clamps Patrick Bellasi
@ 2019-06-21  8:42 ` Patrick Bellasi
  2019-06-21 14:55 ` [PATCH v10 00/16] Add utilization clamping support Patrick Bellasi
  16 siblings, 0 replies; 27+ messages in thread
From: Patrick Bellasi @ 2019-06-21  8:42 UTC (permalink / raw)
  To: linux-kernel, linux-pm
  Cc: Ingo Molnar, Peter Zijlstra, Tejun Heo, Rafael J . Wysocki,
	Vincent Guittot, Viresh Kumar, Paul Turner, Quentin Perret,
	Dietmar Eggemann, Morten Rasmussen, Juri Lelli, Todd Kjos,
	Joel Fernandes, Steve Muckle, Suren Baghdasaryan,
	Alessio Balsini

On updates of task group (TG) clamp values, ensure that these new values
are enforced on all RUNNABLE tasks of the task group, i.e. all RUNNABLE
tasks are immediately boosted and/or clamped as requested.

Do that by slightly refactoring uclamp_bucket_inc(). An additional
parameter *cgroup_subsys_state (css) is used to walk the list of tasks
in the TGs and update the RUNNABLE ones. Do that by taking the rq
lock for each task, the same mechanism used for cpu affinity masks
updates.

Signed-off-by: Patrick Bellasi <patrick.bellasi@arm.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Tejun Heo <tj@kernel.org>
---
 kernel/sched/core.c | 48 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 48 insertions(+)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 8070e11cafa0..1ddc37320f3d 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1032,6 +1032,51 @@ static inline void uclamp_rq_dec(struct rq *rq, struct task_struct *p)
 		uclamp_rq_dec_id(rq, p, clamp_id);
 }
 
+static inline void
+uclamp_update_active(struct task_struct *p, unsigned int clamp_id)
+{
+	struct rq_flags rf;
+	struct rq *rq;
+
+	/*
+	 * Lock the task and the rq where the task is (or was) queued.
+	 *
+	 * We might lock the (previous) rq of a !RUNNABLE task, but that's the
+	 * price to pay to safely serialize util_{min,max} updates with
+	 * enqueues, dequeues and migration operations.
+	 * This is the same locking schema used by __set_cpus_allowed_ptr().
+	 */
+	rq = task_rq_lock(p, &rf);
+
+	/*
+	 * Setting the clamp bucket is serialized by task_rq_lock().
+	 * If the task is not yet RUNNABLE and its task_struct is not
+	 * affecting a valid clamp bucket, the next time it's enqueued,
+	 * it will already see the updated clamp bucket value.
+	 */
+	if (!p->uclamp[clamp_id].active)
+		goto done;
+
+	uclamp_rq_dec_id(rq, p, clamp_id);
+	uclamp_rq_inc_id(rq, p, clamp_id);
+
+done:
+
+	task_rq_unlock(rq, p, &rf);
+}
+
+static inline void
+uclamp_update_active_tasks(struct cgroup_subsys_state *css, int clamp_id)
+{
+	struct css_task_iter it;
+	struct task_struct *p;
+
+	css_task_iter_start(css, 0, &it);
+	while ((p = css_task_iter_next(&it)))
+		uclamp_update_active(p, clamp_id);
+	css_task_iter_end(&it);
+}
+
 #ifdef CONFIG_UCLAMP_TASK_GROUP
 static void cpu_util_update_eff(struct cgroup_subsys_state *css,
 				unsigned int clamp_id);
@@ -7064,6 +7109,9 @@ static void cpu_util_update_eff(struct cgroup_subsys_state *css,
 
 		uc_se->value = value;
 		uc_se->bucket_id = uclamp_bucket_id(value);
+
+		/* Immediately update descendants RUNNABLE tasks */
+		uclamp_update_active_tasks(css, clamp_id);
 	}
 }
 
-- 
2.21.0


^ permalink raw reply	[flat|nested] 27+ messages in thread

* Re: [PATCH v10 11/16] sched/fair: uclamp: Add uclamp support to energy_compute()
  2019-06-21  8:42 ` [PATCH v10 11/16] sched/fair: uclamp: Add uclamp support to energy_compute() Patrick Bellasi
@ 2019-06-21 14:01   ` Peter Zijlstra
  2019-06-21 14:47     ` Patrick Bellasi
  0 siblings, 1 reply; 27+ messages in thread
From: Peter Zijlstra @ 2019-06-21 14:01 UTC (permalink / raw)
  To: Patrick Bellasi
  Cc: linux-kernel, linux-pm, Ingo Molnar, Tejun Heo,
	Rafael J . Wysocki, Vincent Guittot, Viresh Kumar, Paul Turner,
	Quentin Perret, Dietmar Eggemann, Morten Rasmussen, Juri Lelli,
	Todd Kjos, Joel Fernandes, Steve Muckle, Suren Baghdasaryan,
	Alessio Balsini

On Fri, Jun 21, 2019 at 09:42:12AM +0100, Patrick Bellasi wrote:

> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
> index ce2da8b9ff8c..f81e8930ff19 100644
> --- a/kernel/sched/sched.h
> +++ b/kernel/sched/sched.h
> @@ -2322,7 +2322,6 @@ static inline unsigned long capacity_orig_of(int cpu)
>  }
>  #endif
>  
> -#ifdef CONFIG_CPU_FREQ_GOV_SCHEDUTIL
>  /**
>   * enum schedutil_type - CPU utilization type
>   * @FREQUENCY_UTIL:	Utilization used to select frequency
> @@ -2338,15 +2337,11 @@ enum schedutil_type {
>  	ENERGY_UTIL,
>  };
>  
> -unsigned long schedutil_freq_util(int cpu, unsigned long util_cfs,
> -				  unsigned long max, enum schedutil_type type);
> -
> -static inline unsigned long schedutil_energy_util(int cpu, unsigned long cfs)
> -{
> -	unsigned long max = arch_scale_cpu_capacity(NULL, cpu);

That conflicts with the patch I have removing that NULL argument, fixed
it up.

> +#ifdef CONFIG_CPU_FREQ_GOV_SCHEDUTIL
>  
> -	return schedutil_freq_util(cpu, cfs, max, ENERGY_UTIL);
> -}
> +unsigned long schedutil_cpu_util(int cpu, unsigned long util_cfs,
> +				 unsigned long max, enum schedutil_type type,
> +				 struct task_struct *p);
>  
>  static inline unsigned long cpu_bw_dl(struct rq *rq)
>  {
> @@ -2375,11 +2370,8 @@ static inline unsigned long cpu_util_rt(struct rq *rq)
>  	return READ_ONCE(rq->avg_rt.util_avg);
>  }
>  #else /* CONFIG_CPU_FREQ_GOV_SCHEDUTIL */
> -static inline unsigned long schedutil_energy_util(int cpu, unsigned long cfs)
> -{
> -	return cfs;
> -}
> -#endif
> +#define schedutil_cpu_util(cpu, util_cfs, max, type, p) 0

Was there a good reason for this to be a macro and not an inline
function? I've changed it, if it explodes in 0day, it's all my fault ;-)

> +#endif /* CONFIG_CPU_FREQ_GOV_SCHEDUTIL */

^ permalink raw reply	[flat|nested] 27+ messages in thread

* Re: [PATCH v10 11/16] sched/fair: uclamp: Add uclamp support to energy_compute()
  2019-06-21 14:01   ` Peter Zijlstra
@ 2019-06-21 14:47     ` Patrick Bellasi
  0 siblings, 0 replies; 27+ messages in thread
From: Patrick Bellasi @ 2019-06-21 14:47 UTC (permalink / raw)
  To: Peter Zijlstra
  Cc: linux-kernel, linux-pm, Ingo Molnar, Tejun Heo,
	Rafael J . Wysocki, Vincent Guittot, Viresh Kumar, Paul Turner,
	Quentin Perret, Dietmar Eggemann, Morten Rasmussen, Juri Lelli,
	Todd Kjos, Joel Fernandes, Steve Muckle, Suren Baghdasaryan,
	Alessio Balsini

On 21-Jun 16:01, Peter Zijlstra wrote:
> On Fri, Jun 21, 2019 at 09:42:12AM +0100, Patrick Bellasi wrote:
> 
> > diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
> > index ce2da8b9ff8c..f81e8930ff19 100644
> > --- a/kernel/sched/sched.h
> > +++ b/kernel/sched/sched.h
> > @@ -2322,7 +2322,6 @@ static inline unsigned long capacity_orig_of(int cpu)
> >  }
> >  #endif
> >  
> > -#ifdef CONFIG_CPU_FREQ_GOV_SCHEDUTIL
> >  /**
> >   * enum schedutil_type - CPU utilization type
> >   * @FREQUENCY_UTIL:	Utilization used to select frequency
> > @@ -2338,15 +2337,11 @@ enum schedutil_type {
> >  	ENERGY_UTIL,
> >  };
> >  
> > -unsigned long schedutil_freq_util(int cpu, unsigned long util_cfs,
> > -				  unsigned long max, enum schedutil_type type);
> > -
> > -static inline unsigned long schedutil_energy_util(int cpu, unsigned long cfs)
> > -{
> > -	unsigned long max = arch_scale_cpu_capacity(NULL, cpu);
> 
> That conflicts with the patch I have removing that NULL argument, fixed
> it up.

Ok, I notice only know you have this:

   commit 119fd437f412 ("sched/topology: Remove unused sd param from arch_scale_cpu_capacity()")

from Vincent on your queue. :/


> > +#ifdef CONFIG_CPU_FREQ_GOV_SCHEDUTIL
> >  
> > -	return schedutil_freq_util(cpu, cfs, max, ENERGY_UTIL);
> > -}
> > +unsigned long schedutil_cpu_util(int cpu, unsigned long util_cfs,
> > +				 unsigned long max, enum schedutil_type type,
> > +				 struct task_struct *p);
> >  
> >  static inline unsigned long cpu_bw_dl(struct rq *rq)
> >  {
> > @@ -2375,11 +2370,8 @@ static inline unsigned long cpu_util_rt(struct rq *rq)
> >  	return READ_ONCE(rq->avg_rt.util_avg);
> >  }
> >  #else /* CONFIG_CPU_FREQ_GOV_SCHEDUTIL */
> > -static inline unsigned long schedutil_energy_util(int cpu, unsigned long cfs)
> > -{
> > -	return cfs;
> > -}
> > -#endif
> > +#define schedutil_cpu_util(cpu, util_cfs, max, type, p) 0
> 
> Was there a good reason for this to be a macro and not an inline
> function?

Mmm... not really, apart perhaps saving some lines.

I notice sometimes we use macros (e.g. perf_domain_span), but it's
certainly not the most common pattern.

> I've changed it, if it explodes in 0day, it's all my fault ;-)

Sure, I guess if 0day explodes will not be for that change. :)


-- 
#include <best/regards.h>

Patrick Bellasi

^ permalink raw reply	[flat|nested] 27+ messages in thread

* Re: [PATCH v10 00/16] Add utilization clamping support
  2019-06-21  8:42 [PATCH v10 00/16] Add utilization clamping support Patrick Bellasi
                   ` (15 preceding siblings ...)
  2019-06-21  8:42 ` [PATCH v10 16/16] sched/core: uclamp: Update CPU's refcount on TG's clamp changes Patrick Bellasi
@ 2019-06-21 14:55 ` Patrick Bellasi
  16 siblings, 0 replies; 27+ messages in thread
From: Patrick Bellasi @ 2019-06-21 14:55 UTC (permalink / raw)
  To: linux-kernel, linux-pm
  Cc: Ingo Molnar, Peter Zijlstra, Tejun Heo, Rafael J . Wysocki,
	Vincent Guittot, Viresh Kumar, Paul Turner, Quentin Perret,
	Dietmar Eggemann, Morten Rasmussen, Juri Lelli, Todd Kjos,
	Joel Fernandes, Steve Muckle, Suren Baghdasaryan,
	Alessio Balsini

On 21-Jun 09:42, Patrick Bellasi wrote:
> Hi all, this is a respin of:
> 
>   https://lore.kernel.org/lkml/20190515094459.10317-1-patrick.bellasi@arm.com/
> 
> which addresses all Tejun's concerns:
> 
>  - rename cgroup attributes to be cpu.uclamp.{min,max}
>  - update initialization of subgroups clamps to be "no clamps" by default
>  - use percentage rational numbers for clamp attributes, e.g. "12.34" for 12.34%.
> 
> by introducing modifications impacting only patches:
> 
>  [PATCH v10 12/16] sched/core: uclamp: Extend CPU's cgroup controller
>  [PATCH v10 13/16] sched/core: uclamp: Propagate parent clamps
> 
> The rest of the patches are the same as per in v9, they have been just rebased
> on top of:
> 
>    tj/cgroup.git	for-5.3
>    tip/tip.git		sched/core
> 
> AFAIU, all the first 11 patches have been code reviewed and should be at a
> "ready to merge" quality level. Please let me know if I'm wrong and there
> is something else I need/can to do on those patches.
> 
> Otherwise, now that we should have settled all the behavioral aspects, I'm

Regarding the behavioral aspects, here I have a report with some
simple tests for the current implementation:

   https://gist.github.com/derkling/519459b5a2be35d8681fbaf1d6efe225

There are a couple of sections at the end to test the "Delegation
Model" with both CGroups v1 and v2.

I'm sharing the link just in case it can be helpful to verify if what
has been implemented is actually matching what Tejun expects as a sane
cgroups interface.

Cheers,
Patrick

-- 
#include <best/regards.h>

Patrick Bellasi

^ permalink raw reply	[flat|nested] 27+ messages in thread

* Re: [PATCH v10 12/16] sched/core: uclamp: Extend CPU's cgroup controller
  2019-06-21  8:42 ` [PATCH v10 12/16] sched/core: uclamp: Extend CPU's cgroup controller Patrick Bellasi
@ 2019-06-22 15:03   ` Tejun Heo
  2019-06-24 17:29     ` Patrick Bellasi
  0 siblings, 1 reply; 27+ messages in thread
From: Tejun Heo @ 2019-06-22 15:03 UTC (permalink / raw)
  To: Patrick Bellasi
  Cc: linux-kernel, linux-pm, Ingo Molnar, Peter Zijlstra,
	Rafael J . Wysocki, Vincent Guittot, Viresh Kumar, Paul Turner,
	Quentin Perret, Dietmar Eggemann, Morten Rasmussen, Juri Lelli,
	Todd Kjos, Joel Fernandes, Steve Muckle, Suren Baghdasaryan,
	Alessio Balsini

Hello,

Generally looks good to me.  Some nitpicks.

On Fri, Jun 21, 2019 at 09:42:13AM +0100, Patrick Bellasi wrote:
> @@ -951,6 +951,12 @@ controller implements weight and absolute bandwidth limit models for
>  normal scheduling policy and absolute bandwidth allocation model for
>  realtime scheduling policy.
>  
> +Cycles distribution is based, by default, on a temporal base and it
> +does not account for the frequency at which tasks are executed.
> +The (optional) utilization clamping support allows to enforce a minimum
> +bandwidth, which should always be provided by a CPU, and a maximum bandwidth,
> +which should never be exceeded by a CPU.

I kinda wonder whether the term bandwidth is a bit confusing because
it's also used for cpu.max/min.  Would just calling it frequency be
clearer?

> +static ssize_t cpu_uclamp_min_write(struct kernfs_open_file *of,
> +				    char *buf, size_t nbytes,
> +				    loff_t off)
> +{
> +	struct task_group *tg;
> +	u64 min_value;
> +	int ret;
> +
> +	ret = uclamp_scale_from_percent(buf, &min_value);
> +	if (ret)
> +		return ret;
> +	if (min_value > SCHED_CAPACITY_SCALE)
> +		return -ERANGE;
> +
> +	rcu_read_lock();
> +
> +	tg = css_tg(of_css(of));
> +	if (tg == &root_task_group) {
> +		ret = -EINVAL;
> +		goto out;
> +	}

I don't think you need the above check.

> +	if (tg->uclamp_req[UCLAMP_MIN].value == min_value)
> +		goto out;
> +	if (tg->uclamp_req[UCLAMP_MAX].value < min_value) {
> +		ret = -EINVAL;

So, uclamp.max limits the maximum freq% can get and uclamp.min limits
hte maximum freq% protection can get in the subtree.  Let's say
uclamp.max is 50% and uclamp.min is 100%.  It means that protection is
not limited but the actual freq% is limited upto 50%, which isn't
necessarily invalid.  For a simple example, a user might be saying
that they want to get whatever protection they can get from its parent
but wanna limit eventual freq at 50% and it isn't too difficult to
imagine cases where the two knobs are configured separately especially
configuration is being managed hierarchically / automatically.

tl;dr is that we don't need the above restriction and shouldn't
generally be restricting configurations when they don't need to.

Thanks.

-- 
tejun

^ permalink raw reply	[flat|nested] 27+ messages in thread

* Re: [PATCH v10 13/16] sched/core: uclamp: Propagate parent clamps
  2019-06-21  8:42 ` [PATCH v10 13/16] sched/core: uclamp: Propagate parent clamps Patrick Bellasi
@ 2019-06-22 15:07   ` Tejun Heo
  2019-06-24 17:34     ` Patrick Bellasi
  0 siblings, 1 reply; 27+ messages in thread
From: Tejun Heo @ 2019-06-22 15:07 UTC (permalink / raw)
  To: Patrick Bellasi
  Cc: linux-kernel, linux-pm, Ingo Molnar, Peter Zijlstra,
	Rafael J . Wysocki, Vincent Guittot, Viresh Kumar, Paul Turner,
	Quentin Perret, Dietmar Eggemann, Morten Rasmussen, Juri Lelli,
	Todd Kjos, Joel Fernandes, Steve Muckle, Suren Baghdasaryan,
	Alessio Balsini

Hello,

On Fri, Jun 21, 2019 at 09:42:14AM +0100, Patrick Bellasi wrote:
> Since it can be interesting for userspace, e.g. system management
> software, to know exactly what the currently propagated/enforced
> configuration is, the effective clamp values are exposed to user-space
> by means of a new pair of read-only attributes
> cpu.util.{min,max}.effective.

Can we not add the effective interface file for now?  I don't think
it's a bad idea but would like to think more about it.  For cpuset, it
was needed because configuration was so interwoven with the effective
masks, but we don't generally do this for other min/max or weight
knobs, all of which have effective hierarchical values and I'm not
quite sure about adding .effective for all of them.  It could be that
that's what we end up doing eventually but I'd like to think a bit
more about it.

Thanks.

-- 
tejun

^ permalink raw reply	[flat|nested] 27+ messages in thread

* Re: [PATCH v10 12/16] sched/core: uclamp: Extend CPU's cgroup controller
  2019-06-22 15:03   ` Tejun Heo
@ 2019-06-24 17:29     ` Patrick Bellasi
  2019-06-24 17:52       ` Tejun Heo
  0 siblings, 1 reply; 27+ messages in thread
From: Patrick Bellasi @ 2019-06-24 17:29 UTC (permalink / raw)
  To: Tejun Heo
  Cc: linux-kernel, linux-pm, Ingo Molnar, Peter Zijlstra,
	Rafael J . Wysocki, Vincent Guittot, Viresh Kumar, Paul Turner,
	Quentin Perret, Dietmar Eggemann, Morten Rasmussen, Juri Lelli,
	Todd Kjos, Joel Fernandes, Steve Muckle, Suren Baghdasaryan,
	Alessio Balsini

On 22-Jun 08:03, Tejun Heo wrote:
> Hello,

Hi,

> Generally looks good to me.  Some nitpicks.
> 
> On Fri, Jun 21, 2019 at 09:42:13AM +0100, Patrick Bellasi wrote:
> > @@ -951,6 +951,12 @@ controller implements weight and absolute bandwidth limit models for
> >  normal scheduling policy and absolute bandwidth allocation model for
> >  realtime scheduling policy.
> > 
> > +Cycles distribution is based, by default, on a temporal base and it
> > +does not account for the frequency at which tasks are executed.
> > +The (optional) utilization clamping support allows to enforce a minimum
> > +bandwidth, which should always be provided by a CPU, and a maximum bandwidth,
> > +which should never be exceeded by a CPU.
> 
> I kinda wonder whether the term bandwidth is a bit confusing because
> it's also used for cpu.max/min.  Would just calling it frequency be
> clearer?

Maybe I should find a better way to express the concept above.

I agree that bandwidth is already used by cpu.{max,min}, what I want
to call out is that clamps allows to enrich that concept.

By hinting the scheduler on min/max required utilization we can better
defined the amount of actual CPU cycles required/allowed.
That's a bit more precise bandwidth control compared to just rely on
temporal runnable/period limits.

> > +static ssize_t cpu_uclamp_min_write(struct kernfs_open_file *of,
> > +				    char *buf, size_t nbytes,
> > +				    loff_t off)
> > +{
> > +	struct task_group *tg;
> > +	u64 min_value;
> > +	int ret;
> > +
> > +	ret = uclamp_scale_from_percent(buf, &min_value);
> > +	if (ret)
> > +		return ret;
> > +	if (min_value > SCHED_CAPACITY_SCALE)
> > +		return -ERANGE;
> > +
> > +	rcu_read_lock();
> > +
> > +	tg = css_tg(of_css(of));
> > +	if (tg == &root_task_group) {
> > +		ret = -EINVAL;
> > +		goto out;
> > +	}
> 
> I don't think you need the above check.

Don't we want to forbid attributes tuning from the root group?

> > +	if (tg->uclamp_req[UCLAMP_MIN].value == min_value)
> > +		goto out;
> > +	if (tg->uclamp_req[UCLAMP_MAX].value < min_value) {
> > +		ret = -EINVAL;
> 
> So, uclamp.max limits the maximum freq% can get and uclamp.min limits
> hte maximum freq% protection can get in the subtree.  Let's say
> uclamp.max is 50% and uclamp.min is 100%.

That's not possible, in the current implementation we always enforce
the limit (uclamp.max) to be _not smaller_ then the protection
(uclamp.min).

Indeed, in principle, it does not make sense to ask for a minimum
utilization (i.e. frequency boosting) which is higher then the
maximum allowed utilization (i.e. frequency capping).


> It means that protection is not limited but the actual freq% is
> limited upto 50%, which isn't necessarily invalid.
> For a simple example, a user might be saying
> that they want to get whatever protection they can get from its parent
> but wanna limit eventual freq at 50% and it isn't too difficult to
> imagine cases where the two knobs are configured separately especially
> configuration is being managed hierarchically / automatically.

That's not my understanding, in v10 by default when we create a
subgroup we assign it uclamp.min=0%, meaning that we don't boost
frequencies.

It seems instead that you are asking to set uclamp.min=100% by
default, so that the effective value will give us whatever the father
allow. Is that correct?

> tl;dr is that we don't need the above restriction and shouldn't
> generally be restricting configurations when they don't need to.
> 
> Thanks.
> 
> -- 
> tejun

Cheers,
Patrick

-- 
#include <best/regards.h>

Patrick Bellasi

^ permalink raw reply	[flat|nested] 27+ messages in thread

* Re: [PATCH v10 13/16] sched/core: uclamp: Propagate parent clamps
  2019-06-22 15:07   ` Tejun Heo
@ 2019-06-24 17:34     ` Patrick Bellasi
  2019-06-24 17:46       ` Tejun Heo
  0 siblings, 1 reply; 27+ messages in thread
From: Patrick Bellasi @ 2019-06-24 17:34 UTC (permalink / raw)
  To: Tejun Heo
  Cc: linux-kernel, linux-pm, Ingo Molnar, Peter Zijlstra,
	Rafael J . Wysocki, Vincent Guittot, Viresh Kumar, Paul Turner,
	Quentin Perret, Dietmar Eggemann, Morten Rasmussen, Juri Lelli,
	Todd Kjos, Joel Fernandes, Steve Muckle, Suren Baghdasaryan,
	Alessio Balsini

On 22-Jun 08:07, Tejun Heo wrote:
> Hello,

Hi,
 
> On Fri, Jun 21, 2019 at 09:42:14AM +0100, Patrick Bellasi wrote:
> > Since it can be interesting for userspace, e.g. system management
> > software, to know exactly what the currently propagated/enforced
> > configuration is, the effective clamp values are exposed to user-space
> > by means of a new pair of read-only attributes
> > cpu.util.{min,max}.effective.
> 
> Can we not add the effective interface file for now?

You mean just the (read-only) user-space API right?

I found it quite convenient, even just for debugging.
Moreover it allows a container to know what it's exactly getting...

> I don't think it's a bad idea but would like to think more about it.
> For cpuset, it was needed because configuration was so interwoven
> with the effective masks, but we don't generally do this for other
> min/max or weight knobs, all of which have effective hierarchical
> values and I'm not quite sure about adding .effective for all of
> them.
> It could be that that's what we end up doing eventually but
> I'd like to think a bit more about it.

... but I see your point and, since it's not strictly required, I
think we can drop it in v11. Will check better if it's of any use
apart from debugging/testing support.

> Thanks.
> 
> -- 
> tejun

Cheers,
Patrick

-- 
#include <best/regards.h>

Patrick Bellasi

^ permalink raw reply	[flat|nested] 27+ messages in thread

* Re: [PATCH v10 13/16] sched/core: uclamp: Propagate parent clamps
  2019-06-24 17:34     ` Patrick Bellasi
@ 2019-06-24 17:46       ` Tejun Heo
  0 siblings, 0 replies; 27+ messages in thread
From: Tejun Heo @ 2019-06-24 17:46 UTC (permalink / raw)
  To: Patrick Bellasi
  Cc: linux-kernel, linux-pm, Ingo Molnar, Peter Zijlstra,
	Rafael J . Wysocki, Vincent Guittot, Viresh Kumar, Paul Turner,
	Quentin Perret, Dietmar Eggemann, Morten Rasmussen, Juri Lelli,
	Todd Kjos, Joel Fernandes, Steve Muckle, Suren Baghdasaryan,
	Alessio Balsini

Hello, Patrick.

On Mon, Jun 24, 2019 at 06:34:05PM +0100, Patrick Bellasi wrote:
> > On Fri, Jun 21, 2019 at 09:42:14AM +0100, Patrick Bellasi wrote:
> > > Since it can be interesting for userspace, e.g. system management
> > > software, to know exactly what the currently propagated/enforced
> > > configuration is, the effective clamp values are exposed to user-space
> > > by means of a new pair of read-only attributes
> > > cpu.util.{min,max}.effective.
> > 
> > Can we not add the effective interface file for now?
> 
> You mean just the (read-only) user-space API right?

Yeah.

> I found it quite convenient, even just for debugging.
> Moreover it allows a container to know what it's exactly getting...

I fully agree.

> > I don't think it's a bad idea but would like to think more about it.
> > For cpuset, it was needed because configuration was so interwoven
> > with the effective masks, but we don't generally do this for other
> > min/max or weight knobs, all of which have effective hierarchical
> > values and I'm not quite sure about adding .effective for all of
> > them.
> > It could be that that's what we end up doing eventually but
> > I'd like to think a bit more about it.
> 
> ... but I see your point and, since it's not strictly required, I
> think we can drop it in v11. Will check better if it's of any use
> apart from debugging/testing support.

Yeah, I just wanna figure out a plan which works for other controllers
too.  It could be that the right thing to do is just adding .effective
to everything but idk I need to think more about it.

Thanks.

-- 
tejun

^ permalink raw reply	[flat|nested] 27+ messages in thread

* Re: [PATCH v10 12/16] sched/core: uclamp: Extend CPU's cgroup controller
  2019-06-24 17:29     ` Patrick Bellasi
@ 2019-06-24 17:52       ` Tejun Heo
  2019-06-25  9:31         ` Patrick Bellasi
  0 siblings, 1 reply; 27+ messages in thread
From: Tejun Heo @ 2019-06-24 17:52 UTC (permalink / raw)
  To: Patrick Bellasi
  Cc: linux-kernel, linux-pm, Ingo Molnar, Peter Zijlstra,
	Rafael J . Wysocki, Vincent Guittot, Viresh Kumar, Paul Turner,
	Quentin Perret, Dietmar Eggemann, Morten Rasmussen, Juri Lelli,
	Todd Kjos, Joel Fernandes, Steve Muckle, Suren Baghdasaryan,
	Alessio Balsini

Hey, Patrick.

On Mon, Jun 24, 2019 at 06:29:06PM +0100, Patrick Bellasi wrote:
> > I kinda wonder whether the term bandwidth is a bit confusing because
> > it's also used for cpu.max/min.  Would just calling it frequency be
> > clearer?
> 
> Maybe I should find a better way to express the concept above.
> 
> I agree that bandwidth is already used by cpu.{max,min}, what I want
> to call out is that clamps allows to enrich that concept.
> 
> By hinting the scheduler on min/max required utilization we can better
> defined the amount of actual CPU cycles required/allowed.
> That's a bit more precise bandwidth control compared to just rely on
> temporal runnable/period limits.

I see.  I wonder whether it's overloading the same term too subtly
tho.  It's great to document how they interact but it *might* be
easier for readers if a different term is used even if the meaning is
essentially the same.  Anyways, it's a nitpick.  Please feel free to
ignore.

> > > +	tg = css_tg(of_css(of));
> > > +	if (tg == &root_task_group) {
> > > +		ret = -EINVAL;
> > > +		goto out;
> > > +	}
> > 
> > I don't think you need the above check.
> 
> Don't we want to forbid attributes tuning from the root group?

Yeah, that's enforced by NOT_ON_ROOT flag, right?

> > So, uclamp.max limits the maximum freq% can get and uclamp.min limits
> > hte maximum freq% protection can get in the subtree.  Let's say
> > uclamp.max is 50% and uclamp.min is 100%.
> 
> That's not possible, in the current implementation we always enforce
> the limit (uclamp.max) to be _not smaller_ then the protection
> (uclamp.min).
> 
> Indeed, in principle, it does not make sense to ask for a minimum
> utilization (i.e. frequency boosting) which is higher then the
> maximum allowed utilization (i.e. frequency capping).

Yeah, I'm trying to explain actually it does.

> > It means that protection is not limited but the actual freq% is
> > limited upto 50%, which isn't necessarily invalid.
> > For a simple example, a user might be saying
> > that they want to get whatever protection they can get from its parent
> > but wanna limit eventual freq at 50% and it isn't too difficult to
> > imagine cases where the two knobs are configured separately especially
> > configuration is being managed hierarchically / automatically.
> 
> That's not my understanding, in v10 by default when we create a
> subgroup we assign it uclamp.min=0%, meaning that we don't boost
> frequencies.
> 
> It seems instead that you are asking to set uclamp.min=100% by
> default, so that the effective value will give us whatever the father
> allow. Is that correct?

No, the defaults are fine.  I'm trying to say that min/max
configurations don't need to be coupled like this and there are valid
use cases where the configured min is higher than max when
configurations are nested and managed automatically.

Limits always trump protection in effect of course but please don't
limit what can be configured.

Thanks.

-- 
tejun

^ permalink raw reply	[flat|nested] 27+ messages in thread

* Re: [PATCH v10 12/16] sched/core: uclamp: Extend CPU's cgroup controller
  2019-06-24 17:52       ` Tejun Heo
@ 2019-06-25  9:31         ` Patrick Bellasi
  0 siblings, 0 replies; 27+ messages in thread
From: Patrick Bellasi @ 2019-06-25  9:31 UTC (permalink / raw)
  To: Tejun Heo
  Cc: linux-kernel, linux-pm, Ingo Molnar, Peter Zijlstra,
	Rafael J . Wysocki, Vincent Guittot, Viresh Kumar, Paul Turner,
	Quentin Perret, Dietmar Eggemann, Morten Rasmussen, Juri Lelli,
	Todd Kjos, Joel Fernandes, Steve Muckle, Suren Baghdasaryan,
	Alessio Balsini

On 24-Jun 10:52, Tejun Heo wrote:

> Hey, Patrick.

Hi,

> On Mon, Jun 24, 2019 at 06:29:06PM +0100, Patrick Bellasi wrote:
> > > I kinda wonder whether the term bandwidth is a bit confusing because
> > > it's also used for cpu.max/min.  Would just calling it frequency be
> > > clearer?
> > 
> > Maybe I should find a better way to express the concept above.
> > 
> > I agree that bandwidth is already used by cpu.{max,min}, what I want
> > to call out is that clamps allows to enrich that concept.
> > 
> > By hinting the scheduler on min/max required utilization we can better
> > defined the amount of actual CPU cycles required/allowed.
> > That's a bit more precise bandwidth control compared to just rely on
> > temporal runnable/period limits.
> 
> I see.  I wonder whether it's overloading the same term too subtly
> tho.  It's great to document how they interact but it *might* be
> easier for readers if a different term is used even if the meaning is
> essentially the same.  Anyways, it's a nitpick.  Please feel free to
> ignore.

Got it, will try come up with a better description in the v11 to avoid
confusion and better explain the "improvements" without polluting too
much the original concept.

> > > > +	tg = css_tg(of_css(of));
> > > > +	if (tg == &root_task_group) {
> > > > +		ret = -EINVAL;
> > > > +		goto out;
> > > > +	}
> > > 
> > > I don't think you need the above check.
> > 
> > Don't we want to forbid attributes tuning from the root group?
> 
> Yeah, that's enforced by NOT_ON_ROOT flag, right?

Oh right, since we don't show them we can't write them :)

> > > So, uclamp.max limits the maximum freq% can get and uclamp.min limits
> > > hte maximum freq% protection can get in the subtree.  Let's say
> > > uclamp.max is 50% and uclamp.min is 100%.
> > 
> > That's not possible, in the current implementation we always enforce
> > the limit (uclamp.max) to be _not smaller_ then the protection
> > (uclamp.min).
> > 
> > Indeed, in principle, it does not make sense to ask for a minimum
> > utilization (i.e. frequency boosting) which is higher then the
> > maximum allowed utilization (i.e. frequency capping).
> 
> Yeah, I'm trying to explain actually it does.
> 
> > > It means that protection is not limited but the actual freq% is
> > > limited upto 50%, which isn't necessarily invalid.
> > > For a simple example, a user might be saying
> > > that they want to get whatever protection they can get from its parent
> > > but wanna limit eventual freq at 50% and it isn't too difficult to
> > > imagine cases where the two knobs are configured separately especially
> > > configuration is being managed hierarchically / automatically.
> > 
> > That's not my understanding, in v10 by default when we create a
> > subgroup we assign it uclamp.min=0%, meaning that we don't boost
> > frequencies.
> > 
> > It seems instead that you are asking to set uclamp.min=100% by
> > default, so that the effective value will give us whatever the father
> > allow. Is that correct?
> 
> No, the defaults are fine.  I'm trying to say that min/max
> configurations don't need to be coupled like this and there are valid
> use cases where the configured min is higher than max when
> configurations are nested and managed automatically.
> 
> Limits always trump protection in effect of course but please don't
> limit what can be configured.

Got it, thanks!

Will fix it in v11.

> Thanks.
> 
> --
> tejun

Cheers,
Patrick

-- 
#include <best/regards.h>

Patrick Bellasi

^ permalink raw reply	[flat|nested] 27+ messages in thread

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Thread overview: 27+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2019-06-21  8:42 [PATCH v10 00/16] Add utilization clamping support Patrick Bellasi
2019-06-21  8:42 ` [PATCH v10 01/16] sched/core: uclamp: Add CPU's clamp buckets refcounting Patrick Bellasi
2019-06-21  8:42 ` [PATCH v10 02/16] sched/core: uclamp: Add bucket local max tracking Patrick Bellasi
2019-06-21  8:42 ` [PATCH v10 03/16] sched/core: uclamp: Enforce last task's UCLAMP_MAX Patrick Bellasi
2019-06-21  8:42 ` [PATCH v10 04/16] sched/core: uclamp: Add system default clamps Patrick Bellasi
2019-06-21  8:42 ` [PATCH v10 05/16] sched/core: Allow sched_setattr() to use the current policy Patrick Bellasi
2019-06-21  8:42 ` [PATCH v10 06/16] sched/core: uclamp: Extend sched_setattr() to support utilization clamping Patrick Bellasi
2019-06-21  8:42 ` [PATCH v10 07/16] sched/core: uclamp: Reset uclamp values on RESET_ON_FORK Patrick Bellasi
2019-06-21  8:42 ` [PATCH v10 08/16] sched/core: uclamp: Set default clamps for RT tasks Patrick Bellasi
2019-06-21  8:42 ` [PATCH v10 09/16] sched/cpufreq: uclamp: Add clamps for FAIR and " Patrick Bellasi
2019-06-21  8:42 ` [PATCH v10 10/16] sched/core: uclamp: Add uclamp_util_with() Patrick Bellasi
2019-06-21  8:42 ` [PATCH v10 11/16] sched/fair: uclamp: Add uclamp support to energy_compute() Patrick Bellasi
2019-06-21 14:01   ` Peter Zijlstra
2019-06-21 14:47     ` Patrick Bellasi
2019-06-21  8:42 ` [PATCH v10 12/16] sched/core: uclamp: Extend CPU's cgroup controller Patrick Bellasi
2019-06-22 15:03   ` Tejun Heo
2019-06-24 17:29     ` Patrick Bellasi
2019-06-24 17:52       ` Tejun Heo
2019-06-25  9:31         ` Patrick Bellasi
2019-06-21  8:42 ` [PATCH v10 13/16] sched/core: uclamp: Propagate parent clamps Patrick Bellasi
2019-06-22 15:07   ` Tejun Heo
2019-06-24 17:34     ` Patrick Bellasi
2019-06-24 17:46       ` Tejun Heo
2019-06-21  8:42 ` [PATCH v10 14/16] sched/core: uclamp: Propagate system defaults to root group Patrick Bellasi
2019-06-21  8:42 ` [PATCH v10 15/16] sched/core: uclamp: Use TG's clamps to restrict TASK's clamps Patrick Bellasi
2019-06-21  8:42 ` [PATCH v10 16/16] sched/core: uclamp: Update CPU's refcount on TG's clamp changes Patrick Bellasi
2019-06-21 14:55 ` [PATCH v10 00/16] Add utilization clamping support Patrick Bellasi

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