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* [PATCH v13 0/6] Add utilization clamping support (CGroups API)
@ 2019-08-02  9:08 Patrick Bellasi
  2019-08-02  9:08 ` [PATCH v13 1/6] sched/core: uclamp: Extend CPU's cgroup controller Patrick Bellasi
                   ` (6 more replies)
  0 siblings, 7 replies; 15+ messages in thread
From: Patrick Bellasi @ 2019-08-02  9:08 UTC (permalink / raw)
  To: linux-kernel, linux-pm, linux-api, cgroups
  Cc: Ingo Molnar, Peter Zijlstra, Tejun Heo, Rafael J . Wysocki,
	Vincent Guittot, Viresh Kumar, Paul Turner, Michal Koutny,
	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/20190718181748.28446-1-patrick.bellasi@arm.com/

which introduces these small changes:

- move common code from cpu_uclamp_{min,max}_write() into
  cpu_uclamp_write(clamp_id)
- comment rewording: update all RUNNABLE tasks on system default changes only
  when cgroups are in use.

The series is based on top of today's tip/sched/core:

  commit a1dc0446d649 ("sched/core: Silence a warning in sched_init()")

Thanks Michal for your additional review!

Since Tejun seems to be happy regarding cgroup integration:

   https://lore.kernel.org/lkml/20190729200606.GA136335@devbig004.ftw2.facebook.com/

and the are no substantial changes in the code functionalities with respect to
v12, this series adds Tejun's ACK tag.

Cheers,
Patrick


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

The full tree is available here:

   git://linux-arm.org/linux-pb.git   lkml/utilclamp_v13
   http://www.linux-arm.org/git?p=linux-pb.git;a=shortlog;h=refs/heads/lkml/utilclamp_v13


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 [1].

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

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


Patrick Bellasi (6):
  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
  sched/core: uclamp: always use enum uclamp_id for clamp_id values

 Documentation/admin-guide/cgroup-v2.rst |  34 +++
 init/Kconfig                            |  22 ++
 kernel/sched/core.c                     | 375 ++++++++++++++++++++++--
 kernel/sched/sched.h                    |  12 +-
 4 files changed, 421 insertions(+), 22 deletions(-)

-- 
2.22.0


^ permalink raw reply	[flat|nested] 15+ messages in thread

* [PATCH v13 1/6] sched/core: uclamp: Extend CPU's cgroup controller
  2019-08-02  9:08 [PATCH v13 0/6] Add utilization clamping support (CGroups API) Patrick Bellasi
@ 2019-08-02  9:08 ` Patrick Bellasi
  2019-08-06 16:11   ` Michal Koutný
  2019-08-02  9:08 ` [PATCH v13 2/6] sched/core: uclamp: Propagate parent clamps Patrick Bellasi
                   ` (5 subsequent siblings)
  6 siblings, 1 reply; 15+ messages in thread
From: Patrick Bellasi @ 2019-08-02  9:08 UTC (permalink / raw)
  To: linux-kernel, linux-pm, linux-api, cgroups
  Cc: Ingo Molnar, Peter Zijlstra, Tejun Heo, Rafael J . Wysocki,
	Vincent Guittot, Viresh Kumar, Paul Turner, Michal Koutny,
	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>
Acked-by: Tejun Heo <tj@kernel.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Tejun Heo <tj@kernel.org>

---
Changes in v13:
 Message-ID: <20190725114104.GA32159@blackbody.suse.cz>
 - move common code from cpu_uclamp_{min,max}_write() into cpu_uclamp_write(clamp_id)
---
 Documentation/admin-guide/cgroup-v2.rst |  34 +++++
 init/Kconfig                            |  22 ++++
 kernel/sched/core.c                     | 167 +++++++++++++++++++++++-
 kernel/sched/sched.h                    |   8 ++
 4 files changed, 230 insertions(+), 1 deletion(-)

diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst
index 3b29005aa981..5f1c266131b0 100644
--- a/Documentation/admin-guide/cgroup-v2.rst
+++ b/Documentation/admin-guide/cgroup-v2.rst
@@ -951,6 +951,13 @@ controller implements weight and absolute bandwidth limit models for
 normal scheduling policy and absolute bandwidth allocation model for
 realtime scheduling policy.
 
+In all the above models, cycles distribution is defined only on a temporal
+base and it does not account for the frequency at which tasks are executed.
+The (optional) utilization clamping support allows to hint the schedutil
+cpufreq governor about the minimum desired frequency which should always be
+provided by a CPU, as well as the maximum desired frequency, which should not
+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 +1023,33 @@ All time durations are in microseconds.
 	Shows pressure stall information for CPU. See
 	Documentation/accounting/psi.rst 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 (protection) 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.
+
+        The requested minimum utilization (protection) is always capped by
+        the current value for the maximum utilization (limit), i.e.
+        `cpu.uclamp.max`.
+
+  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 (limit) 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 bd7d650d4a99..ac285cfa78b6 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -928,6 +928,28 @@ 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 46f3ca9e392a..40cd7567e4d9 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1149,8 +1149,12 @@ 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 */
@@ -6786,6 +6790,19 @@ 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);
@@ -6809,6 +6826,8 @@ 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:
@@ -7025,6 +7044,124 @@ static void cpu_cgroup_attach(struct cgroup_taskset *tset)
 		sched_move_task(task);
 }
 
+#ifdef CONFIG_UCLAMP_TASK_GROUP
+
+#define _POW10(exp) ((unsigned int)1e##exp)
+#define POW10(exp) _POW10(exp)
+
+struct uclamp_request {
+#define UCLAMP_PERCENT_SHIFT	2
+#define UCLAMP_PERCENT_SCALE	(100 * POW10(UCLAMP_PERCENT_SHIFT))
+	s64 percent;
+	u64 util;
+	int ret;
+};
+
+static inline struct uclamp_request
+capacity_from_percent(char *buf)
+{
+	struct uclamp_request req = {
+		.percent = UCLAMP_PERCENT_SCALE,
+		.util = SCHED_CAPACITY_SCALE,
+		.ret = 0,
+	};
+
+	buf = strim(buf);
+	if (strncmp("max", buf, 4)) {
+		req.ret = cgroup_parse_float(buf, UCLAMP_PERCENT_SHIFT,
+					     &req.percent);
+		if (req.ret)
+			return req;
+		if (req.percent > UCLAMP_PERCENT_SCALE) {
+			req.ret = -ERANGE;
+			return req;
+		}
+
+		req.util = req.percent << SCHED_CAPACITY_SHIFT;
+		req.util = DIV_ROUND_CLOSEST_ULL(req.util, UCLAMP_PERCENT_SCALE);
+	}
+
+	return req;
+}
+
+static ssize_t cpu_uclamp_write(struct kernfs_open_file *of, char *buf,
+				size_t nbytes, loff_t off,
+				enum uclamp_id clamp_id)
+{
+	struct uclamp_request req;
+	struct task_group *tg;
+
+	req = capacity_from_percent(buf);
+	if (req.ret)
+		return req.ret;
+
+	rcu_read_lock();
+
+	tg = css_tg(of_css(of));
+	if (tg->uclamp_req[clamp_id].value != req.util)
+		uclamp_se_set(&tg->uclamp_req[clamp_id], req.util, false);
+
+	/*
+	 * Because of not recoverable conversion rounding we keep track of the
+	 * exact requested value
+	 */
+	tg->uclamp_pct[clamp_id] = req.percent;
+
+	rcu_read_unlock();
+
+	return nbytes;
+}
+
+static ssize_t cpu_uclamp_min_write(struct kernfs_open_file *of,
+				    char *buf, size_t nbytes,
+				    loff_t off)
+{
+	return cpu_uclamp_write(of, buf, nbytes, off, UCLAMP_MIN);
+}
+
+static ssize_t cpu_uclamp_max_write(struct kernfs_open_file *of,
+				    char *buf, size_t nbytes,
+				    loff_t off)
+{
+	return cpu_uclamp_write(of, buf, nbytes, off, UCLAMP_MAX);
+}
+
+static inline void cpu_uclamp_print(struct seq_file *sf,
+				    enum uclamp_id clamp_id)
+{
+	struct task_group *tg;
+	u64 util_clamp;
+	u64 percent;
+	u32 rem;
+
+	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 = tg->uclamp_pct[clamp_id];
+	percent = div_u64_rem(percent, POW10(UCLAMP_PERCENT_SHIFT), &rem);
+	seq_printf(sf, "%llu.%0*u\n", percent, UCLAMP_PERCENT_SHIFT, rem);
+}
+
+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)
@@ -7369,6 +7506,20 @@ 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 */
 };
@@ -7536,6 +7687,20 @@ 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 7583faddba33..45c6d7e1e3ed 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -393,6 +393,14 @@ struct task_group {
 #endif
 
 	struct cfs_bandwidth	cfs_bandwidth;
+
+#ifdef CONFIG_UCLAMP_TASK_GROUP
+	/* The two decimal precision [%] value requested from user-space */
+	unsigned int		uclamp_pct[UCLAMP_CNT];
+	/* Clamp values requested for a task group */
+	struct uclamp_se	uclamp_req[UCLAMP_CNT];
+#endif
+
 };
 
 #ifdef CONFIG_FAIR_GROUP_SCHED
-- 
2.22.0


^ permalink raw reply	[flat|nested] 15+ messages in thread

* [PATCH v13 2/6] sched/core: uclamp: Propagate parent clamps
  2019-08-02  9:08 [PATCH v13 0/6] Add utilization clamping support (CGroups API) Patrick Bellasi
  2019-08-02  9:08 ` [PATCH v13 1/6] sched/core: uclamp: Extend CPU's cgroup controller Patrick Bellasi
@ 2019-08-02  9:08 ` Patrick Bellasi
  2019-08-06 16:11   ` Michal Koutný
  2019-08-02  9:08 ` [PATCH v13 3/6] sched/core: uclamp: Propagate system defaults to root group Patrick Bellasi
                   ` (4 subsequent siblings)
  6 siblings, 1 reply; 15+ messages in thread
From: Patrick Bellasi @ 2019-08-02  9:08 UTC (permalink / raw)
  To: linux-kernel, linux-pm, linux-api, cgroups
  Cc: Ingo Molnar, Peter Zijlstra, Tejun Heo, Rafael J . Wysocki,
	Vincent Guittot, Viresh Kumar, Paul Turner, Michal Koutny,
	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 locally consistent and constrained based on parent's
assigned resources. This requires to properly propagate and aggregate
parent attributes down to its descendants.

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's possible for a cpu.uclamp.min value to be bigger than the
cpu.uclamp.max value, ensure local consistency by restricting each
"protection" (i.e. min utilization) with the corresponding "limit"
(i.e. max utilization).

Do that at effective clamps propagation to ensure all user-space write
never fails while still always tracking the most restrictive values.

Update sysctl_sched_uclamp_handler() to use the newly introduced
uclamp_mutex so that we serialize system default updates with cgroup
relate updates.

Signed-off-by: Patrick Bellasi <patrick.bellasi@arm.com>
Acked-by: Tejun Heo <tj@kernel.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Tejun Heo <tj@kernel.org>
---
 kernel/sched/core.c  | 65 ++++++++++++++++++++++++++++++++++++++++++--
 kernel/sched/sched.h |  2 ++
 2 files changed, 64 insertions(+), 3 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 40cd7567e4d9..de8886ce0f65 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -773,6 +773,18 @@ 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;
 
@@ -1010,10 +1022,9 @@ int sysctl_sched_uclamp_handler(struct ctl_table *table, int write,
 				loff_t *ppos)
 {
 	int old_min, old_max;
-	static DEFINE_MUTEX(mutex);
 	int result;
 
-	mutex_lock(&mutex);
+	mutex_lock(&uclamp_mutex);
 	old_min = sysctl_sched_uclamp_util_min;
 	old_max = sysctl_sched_uclamp_util_max;
 
@@ -1048,7 +1059,7 @@ int sysctl_sched_uclamp_handler(struct ctl_table *table, int write,
 	sysctl_sched_uclamp_util_min = old_min;
 	sysctl_sched_uclamp_util_max = old_max;
 done:
-	mutex_unlock(&mutex);
+	mutex_unlock(&uclamp_mutex);
 
 	return result;
 }
@@ -1137,6 +1148,8 @@ 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;
@@ -1153,6 +1166,7 @@ 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
 	}
 }
@@ -6799,6 +6813,7 @@ 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
 }
@@ -7045,6 +7060,45 @@ 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)
+{
+	struct cgroup_subsys_state *top_css = css;
+	struct uclamp_se *uc_parent = NULL;
+	struct uclamp_se *uc_se = NULL;
+	unsigned int eff[UCLAMP_CNT];
+	unsigned int clamp_id;
+	unsigned int clamps;
+
+	css_for_each_descendant_pre(css, top_css) {
+		uc_parent = css_tg(css)->parent
+			? css_tg(css)->parent->uclamp : NULL;
+
+		for_each_clamp_id(clamp_id) {
+			/* Assume effective clamps matches requested clamps */
+			eff[clamp_id] = css_tg(css)->uclamp_req[clamp_id].value;
+			/* Cap effective clamps with parent's effective clamps */
+			if (uc_parent &&
+			    eff[clamp_id] > uc_parent[clamp_id].value) {
+				eff[clamp_id] = uc_parent[clamp_id].value;
+			}
+		}
+		/* Ensure protection is always capped by limit */
+		eff[UCLAMP_MIN] = min(eff[UCLAMP_MIN], eff[UCLAMP_MAX]);
+
+		/* Propagate most restrictive effective clamps */
+		clamps = 0x0;
+		uc_se = css_tg(css)->uclamp;
+		for_each_clamp_id(clamp_id) {
+			if (eff[clamp_id] == uc_se[clamp_id].value)
+				continue;
+			uc_se[clamp_id].value = eff[clamp_id];
+			uc_se[clamp_id].bucket_id = uclamp_bucket_id(eff[clamp_id]);
+			clamps |= (0x1 << clamp_id);
+		}
+		if (!clamps)
+			css = css_rightmost_descendant(css);
+	}
+}
 
 #define _POW10(exp) ((unsigned int)1e##exp)
 #define POW10(exp) _POW10(exp)
@@ -7095,6 +7149,7 @@ static ssize_t cpu_uclamp_write(struct kernfs_open_file *of, char *buf,
 	if (req.ret)
 		return req.ret;
 
+	mutex_lock(&uclamp_mutex);
 	rcu_read_lock();
 
 	tg = css_tg(of_css(of));
@@ -7107,7 +7162,11 @@ static ssize_t cpu_uclamp_write(struct kernfs_open_file *of, char *buf,
 	 */
 	tg->uclamp_pct[clamp_id] = req.percent;
 
+	/* Update effective clamps to track the most restrictive value */
+	cpu_util_update_eff(of_css(of));
+
 	rcu_read_unlock();
+	mutex_unlock(&uclamp_mutex);
 
 	return nbytes;
 }
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 45c6d7e1e3ed..452541efdac1 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -399,6 +399,8 @@ struct task_group {
 	unsigned int		uclamp_pct[UCLAMP_CNT];
 	/* 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
 
 };
-- 
2.22.0


^ permalink raw reply	[flat|nested] 15+ messages in thread

* [PATCH v13 3/6] sched/core: uclamp: Propagate system defaults to root group
  2019-08-02  9:08 [PATCH v13 0/6] Add utilization clamping support (CGroups API) Patrick Bellasi
  2019-08-02  9:08 ` [PATCH v13 1/6] sched/core: uclamp: Extend CPU's cgroup controller Patrick Bellasi
  2019-08-02  9:08 ` [PATCH v13 2/6] sched/core: uclamp: Propagate parent clamps Patrick Bellasi
@ 2019-08-02  9:08 ` Patrick Bellasi
  2019-08-02  9:08 ` [PATCH v13 4/6] sched/core: uclamp: Use TG's clamps to restrict TASK's clamps Patrick Bellasi
                   ` (3 subsequent siblings)
  6 siblings, 0 replies; 15+ messages in thread
From: Patrick Bellasi @ 2019-08-02  9:08 UTC (permalink / raw)
  To: linux-kernel, linux-pm, linux-api, cgroups
  Cc: Ingo Molnar, Peter Zijlstra, Tejun Heo, Rafael J . Wysocki,
	Vincent Guittot, Viresh Kumar, Paul Turner, Michal Koutny,
	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.

When cgroups are in use, force an update of all the RUNNABLE tasks.
Otherwise, keep things simple and do just a lazy update next time each
task will be enqueued.
Do that since we assume a more strict resource control is required when
cgroups are in use. This allows also to keep "effective" clamp values
updated in case we need to expose them to user-space.

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

---
Changes in v13:
 Message-ID: <20190725114126.GA4130@blackbody.suse.cz>
 - comment rewording: update all RUNNABLE tasks on system default
   changes only when cgroups are in use.
---
 kernel/sched/core.c | 31 +++++++++++++++++++++++++++++--
 1 file changed, 29 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index de8886ce0f65..5683c8639b4a 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1017,10 +1017,30 @@ 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);
+static void uclamp_update_root_tg(void)
+{
+	struct task_group *tg = &root_task_group;
+
+	uclamp_se_set(&tg->uclamp_req[UCLAMP_MIN],
+		      sysctl_sched_uclamp_util_min, false);
+	uclamp_se_set(&tg->uclamp_req[UCLAMP_MAX],
+		      sysctl_sched_uclamp_util_max, false);
+
+	rcu_read_lock();
+	cpu_util_update_eff(&root_task_group.css);
+	rcu_read_unlock();
+}
+#else
+static void uclamp_update_root_tg(void) { }
+#endif
+
 int sysctl_sched_uclamp_handler(struct ctl_table *table, int write,
 				void __user *buffer, size_t *lenp,
 				loff_t *ppos)
 {
+	bool update_root_tg = false;
 	int old_min, old_max;
 	int result;
 
@@ -1043,16 +1063,23 @@ 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, false);
+		update_root_tg = true;
 	}
 	if (old_max != sysctl_sched_uclamp_util_max) {
 		uclamp_se_set(&uclamp_default[UCLAMP_MAX],
 			      sysctl_sched_uclamp_util_max, false);
+		update_root_tg = true;
 	}
 
+	if (update_root_tg)
+		uclamp_update_root_tg();
+
 	/*
-	 * Updating all the RUNNABLE task is expensive, keep it simple and do
-	 * just a lazy update at each next enqueue time.
+	 * We update all RUNNABLE tasks only when task groups are in use.
+	 * Otherwise, keep it simple and do just a lazy update at each next
+	 * task enqueue time.
 	 */
+
 	goto done;
 
 undo:
-- 
2.22.0


^ permalink raw reply	[flat|nested] 15+ messages in thread

* [PATCH v13 4/6] sched/core: uclamp: Use TG's clamps to restrict TASK's clamps
  2019-08-02  9:08 [PATCH v13 0/6] Add utilization clamping support (CGroups API) Patrick Bellasi
                   ` (2 preceding siblings ...)
  2019-08-02  9:08 ` [PATCH v13 3/6] sched/core: uclamp: Propagate system defaults to root group Patrick Bellasi
@ 2019-08-02  9:08 ` Patrick Bellasi
  2019-08-02  9:08 ` [PATCH v13 5/6] sched/core: uclamp: Update CPU's refcount on TG's clamp changes Patrick Bellasi
                   ` (2 subsequent siblings)
  6 siblings, 0 replies; 15+ messages in thread
From: Patrick Bellasi @ 2019-08-02  9:08 UTC (permalink / raw)
  To: linux-kernel, linux-pm, linux-api, cgroups
  Cc: Ingo Molnar, Peter Zijlstra, Tejun Heo, Rafael J . Wysocki,
	Vincent Guittot, Viresh Kumar, Paul Turner, Michal Koutny,
	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 tracking 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 not more than its TG effective protection and capped at
   least as its TG effective limit.

2. implement a "nice-like" policy, where tasks are still allowed to request
   less than what enforced by their TG effective limits and protections

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, system
defaults are still enforced.

Signed-off-by: Patrick Bellasi <patrick.bellasi@arm.com>
Acked-by: Tejun Heo <tj@kernel.org>
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 5683c8639b4a..106cf69d70cc 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -873,16 +873,42 @@ 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 */
-- 
2.22.0


^ permalink raw reply	[flat|nested] 15+ messages in thread

* [PATCH v13 5/6] sched/core: uclamp: Update CPU's refcount on TG's clamp changes
  2019-08-02  9:08 [PATCH v13 0/6] Add utilization clamping support (CGroups API) Patrick Bellasi
                   ` (3 preceding siblings ...)
  2019-08-02  9:08 ` [PATCH v13 4/6] sched/core: uclamp: Use TG's clamps to restrict TASK's clamps Patrick Bellasi
@ 2019-08-02  9:08 ` Patrick Bellasi
  2019-08-02  9:08 ` [PATCH v13 6/6] sched/core: uclamp: always use enum uclamp_id for clamp_id values Patrick Bellasi
  2019-08-06 16:12 ` [PATCH v13 0/6] Add utilization clamping support (CGroups API) Michal Koutný
  6 siblings, 0 replies; 15+ messages in thread
From: Patrick Bellasi @ 2019-08-02  9:08 UTC (permalink / raw)
  To: linux-kernel, linux-pm, linux-api, cgroups
  Cc: Ingo Molnar, Peter Zijlstra, Tejun Heo, Rafael J . Wysocki,
	Vincent Guittot, Viresh Kumar, Paul Turner, Michal Koutny,
	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 capped as requested.

Do that each time we update effective clamps from cpu_util_update_eff().
Use the *cgroup_subsys_state (css) to walk the list of tasks in each
affected TG and update their RUNNABLE tasks.
Update each task by using the same mechanism used for cpu affinity masks
updates, i.e. by taking the rq lock.

Signed-off-by: Patrick Bellasi <patrick.bellasi@arm.com>
Acked-by: Tejun Heo <tj@kernel.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Tejun Heo <tj@kernel.org>
---
 kernel/sched/core.c | 58 ++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 57 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 106cf69d70cc..8cc1198e7199 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1043,6 +1043,57 @@ 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,
+			   unsigned int clamps)
+{
+	struct css_task_iter it;
+	struct task_struct *p;
+	unsigned int clamp_id;
+
+	css_task_iter_start(css, 0, &it);
+	while ((p = css_task_iter_next(&it))) {
+		for_each_clamp_id(clamp_id) {
+			if ((0x1 << clamp_id) & clamps)
+				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);
 static void uclamp_update_root_tg(void)
@@ -7148,8 +7199,13 @@ static void cpu_util_update_eff(struct cgroup_subsys_state *css)
 			uc_se[clamp_id].bucket_id = uclamp_bucket_id(eff[clamp_id]);
 			clamps |= (0x1 << clamp_id);
 		}
-		if (!clamps)
+		if (!clamps) {
 			css = css_rightmost_descendant(css);
+			continue;
+		}
+
+		/* Immediately update descendants RUNNABLE tasks */
+		uclamp_update_active_tasks(css, clamps);
 	}
 }
 
-- 
2.22.0


^ permalink raw reply	[flat|nested] 15+ messages in thread

* [PATCH v13 6/6] sched/core: uclamp: always use enum uclamp_id for clamp_id values
  2019-08-02  9:08 [PATCH v13 0/6] Add utilization clamping support (CGroups API) Patrick Bellasi
                   ` (4 preceding siblings ...)
  2019-08-02  9:08 ` [PATCH v13 5/6] sched/core: uclamp: Update CPU's refcount on TG's clamp changes Patrick Bellasi
@ 2019-08-02  9:08 ` Patrick Bellasi
  2019-08-06 16:12 ` [PATCH v13 0/6] Add utilization clamping support (CGroups API) Michal Koutný
  6 siblings, 0 replies; 15+ messages in thread
From: Patrick Bellasi @ 2019-08-02  9:08 UTC (permalink / raw)
  To: linux-kernel, linux-pm, linux-api, cgroups
  Cc: Ingo Molnar, Peter Zijlstra, Tejun Heo, Rafael J . Wysocki,
	Vincent Guittot, Viresh Kumar, Paul Turner, Michal Koutny,
	Quentin Perret, Dietmar Eggemann, Morten Rasmussen, Juri Lelli,
	Todd Kjos, Joel Fernandes, Steve Muckle, Suren Baghdasaryan,
	Alessio Balsini

The supported clamp indexes are defined in enum clamp_id however, because
of the code logic in some of the first utilization clamping series version,
sometimes we needed to use unsigned int to represent indexes.

This is not more required since the final version of the uclamp_* APIs can
always use the proper enum uclamp_id type.

Fix it with a bulk rename now that we have all the bits merged.

Signed-off-by: Patrick Bellasi <patrick.bellasi@arm.com>
Acked-by: Tejun Heo <tj@kernel.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
---
 kernel/sched/core.c  | 38 +++++++++++++++++++-------------------
 kernel/sched/sched.h |  2 +-
 2 files changed, 20 insertions(+), 20 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 8cc1198e7199..b6241b6ac133 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -810,7 +810,7 @@ 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)
+static inline enum uclamp_id uclamp_none(enum uclamp_id clamp_id)
 {
 	if (clamp_id == UCLAMP_MIN)
 		return 0;
@@ -826,7 +826,7 @@ static inline void uclamp_se_set(struct uclamp_se *uc_se,
 }
 
 static inline unsigned int
-uclamp_idle_value(struct rq *rq, unsigned int clamp_id,
+uclamp_idle_value(struct rq *rq, enum uclamp_id clamp_id,
 		  unsigned int clamp_value)
 {
 	/*
@@ -842,7 +842,7 @@ uclamp_idle_value(struct rq *rq, unsigned int clamp_id,
 	return uclamp_none(UCLAMP_MIN);
 }
 
-static inline void uclamp_idle_reset(struct rq *rq, unsigned int clamp_id,
+static inline void uclamp_idle_reset(struct rq *rq, enum uclamp_id clamp_id,
 				     unsigned int clamp_value)
 {
 	/* Reset max-clamp retention only on idle exit */
@@ -853,8 +853,8 @@ static inline void uclamp_idle_reset(struct rq *rq, unsigned int clamp_id,
 }
 
 static inline
-unsigned int uclamp_rq_max_value(struct rq *rq, unsigned int clamp_id,
-				 unsigned int clamp_value)
+enum uclamp_id uclamp_rq_max_value(struct rq *rq, enum uclamp_id clamp_id,
+				   unsigned int clamp_value)
 {
 	struct uclamp_bucket *bucket = rq->uclamp[clamp_id].bucket;
 	int bucket_id = UCLAMP_BUCKETS - 1;
@@ -874,7 +874,7 @@ unsigned int uclamp_rq_max_value(struct rq *rq, unsigned int clamp_id,
 }
 
 static inline struct uclamp_se
-uclamp_tg_restrict(struct task_struct *p, unsigned int clamp_id)
+uclamp_tg_restrict(struct task_struct *p, enum uclamp_id clamp_id)
 {
 	struct uclamp_se uc_req = p->uclamp_req[clamp_id];
 #ifdef CONFIG_UCLAMP_TASK_GROUP
@@ -906,7 +906,7 @@ uclamp_tg_restrict(struct task_struct *p, unsigned int clamp_id)
  * - 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)
+uclamp_eff_get(struct task_struct *p, enum uclamp_id clamp_id)
 {
 	struct uclamp_se uc_req = uclamp_tg_restrict(p, clamp_id);
 	struct uclamp_se uc_max = uclamp_default[clamp_id];
@@ -918,7 +918,7 @@ 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)
+enum uclamp_id uclamp_eff_value(struct task_struct *p, enum uclamp_id clamp_id)
 {
 	struct uclamp_se uc_eff;
 
@@ -942,7 +942,7 @@ unsigned int uclamp_eff_value(struct task_struct *p, unsigned int clamp_id)
  * 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)
+				    enum uclamp_id clamp_id)
 {
 	struct uclamp_rq *uc_rq = &rq->uclamp[clamp_id];
 	struct uclamp_se *uc_se = &p->uclamp[clamp_id];
@@ -980,7 +980,7 @@ static inline void uclamp_rq_inc_id(struct rq *rq, struct task_struct *p,
  * enforce the expected state and warn.
  */
 static inline void uclamp_rq_dec_id(struct rq *rq, struct task_struct *p,
-				    unsigned int clamp_id)
+				    enum uclamp_id clamp_id)
 {
 	struct uclamp_rq *uc_rq = &rq->uclamp[clamp_id];
 	struct uclamp_se *uc_se = &p->uclamp[clamp_id];
@@ -1019,7 +1019,7 @@ static inline void uclamp_rq_dec_id(struct rq *rq, struct task_struct *p,
 
 static inline void uclamp_rq_inc(struct rq *rq, struct task_struct *p)
 {
-	unsigned int clamp_id;
+	enum uclamp_id clamp_id;
 
 	if (unlikely(!p->sched_class->uclamp_enabled))
 		return;
@@ -1034,7 +1034,7 @@ 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)
 {
-	unsigned int clamp_id;
+	enum uclamp_id clamp_id;
 
 	if (unlikely(!p->sched_class->uclamp_enabled))
 		return;
@@ -1044,7 +1044,7 @@ static inline void uclamp_rq_dec(struct rq *rq, struct task_struct *p)
 }
 
 static inline void
-uclamp_update_active(struct task_struct *p, unsigned int clamp_id)
+uclamp_update_active(struct task_struct *p, enum uclamp_id clamp_id)
 {
 	struct rq_flags rf;
 	struct rq *rq;
@@ -1080,9 +1080,9 @@ static inline void
 uclamp_update_active_tasks(struct cgroup_subsys_state *css,
 			   unsigned int clamps)
 {
+	enum uclamp_id clamp_id;
 	struct css_task_iter it;
 	struct task_struct *p;
-	unsigned int clamp_id;
 
 	css_task_iter_start(css, 0, &it);
 	while ((p = css_task_iter_next(&it))) {
@@ -1190,7 +1190,7 @@ 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;
+	enum uclamp_id clamp_id;
 
 	/*
 	 * On scheduling class change, reset to default clamps for tasks
@@ -1227,7 +1227,7 @@ static void __setscheduler_uclamp(struct task_struct *p,
 
 static void uclamp_fork(struct task_struct *p)
 {
-	unsigned int clamp_id;
+	enum uclamp_id clamp_id;
 
 	for_each_clamp_id(clamp_id)
 		p->uclamp[clamp_id].active = false;
@@ -1249,7 +1249,7 @@ static void uclamp_fork(struct task_struct *p)
 static void __init init_uclamp(void)
 {
 	struct uclamp_se uc_max = {};
-	unsigned int clamp_id;
+	enum uclamp_id clamp_id;
 	int cpu;
 
 	mutex_init(&uclamp_mutex);
@@ -6912,7 +6912,7 @@ static inline void alloc_uclamp_sched_group(struct task_group *tg,
 					    struct task_group *parent)
 {
 #ifdef CONFIG_UCLAMP_TASK_GROUP
-	int clamp_id;
+	enum uclamp_id clamp_id;
 
 	for_each_clamp_id(clamp_id) {
 		uclamp_se_set(&tg->uclamp_req[clamp_id],
@@ -7170,7 +7170,7 @@ static void cpu_util_update_eff(struct cgroup_subsys_state *css)
 	struct uclamp_se *uc_parent = NULL;
 	struct uclamp_se *uc_se = NULL;
 	unsigned int eff[UCLAMP_CNT];
-	unsigned int clamp_id;
+	enum uclamp_id clamp_id;
 	unsigned int clamps;
 
 	css_for_each_descendant_pre(css, top_css) {
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 452541efdac1..c74fc79b1730 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -2276,7 +2276,7 @@ static inline void cpufreq_update_util(struct rq *rq, unsigned int flags) {}
 #endif /* CONFIG_CPU_FREQ */
 
 #ifdef CONFIG_UCLAMP_TASK
-unsigned int uclamp_eff_value(struct task_struct *p, unsigned int clamp_id);
+enum uclamp_id uclamp_eff_value(struct task_struct *p, enum uclamp_id clamp_id);
 
 static __always_inline
 unsigned int uclamp_util_with(struct rq *rq, unsigned int util,
-- 
2.22.0


^ permalink raw reply	[flat|nested] 15+ messages in thread

* Re: [PATCH v13 1/6] sched/core: uclamp: Extend CPU's cgroup controller
  2019-08-02  9:08 ` [PATCH v13 1/6] sched/core: uclamp: Extend CPU's cgroup controller Patrick Bellasi
@ 2019-08-06 16:11   ` Michal Koutný
  2019-08-08 15:10     ` Patrick Bellasi
  0 siblings, 1 reply; 15+ messages in thread
From: Michal Koutný @ 2019-08-06 16:11 UTC (permalink / raw)
  To: Patrick Bellasi
  Cc: linux-kernel, linux-pm, linux-api, cgroups, 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 Fri, Aug 02, 2019 at 10:08:48AM +0100, Patrick Bellasi <patrick.bellasi@arm.com> wrote:
> +static ssize_t cpu_uclamp_write(struct kernfs_open_file *of, char *buf,
> +				size_t nbytes, loff_t off,
> +				enum uclamp_id clamp_id)
> +{
> +	struct uclamp_request req;
> +	struct task_group *tg;
> +
> +	req = capacity_from_percent(buf);
> +	if (req.ret)
> +		return req.ret;
> +
> +	rcu_read_lock();
This should be the uclamp_mutex.

(The compound results of the series is correct as the lock is introduced
in "sched/core: uclamp: Propagate parent clamps".
This is just for the happiness of cherry-pickers/bisectors.)

> +static inline void cpu_uclamp_print(struct seq_file *sf,
> +				    enum uclamp_id clamp_id)
> +{
> [...]
> +	rcu_read_lock();
> +	tg = css_tg(seq_css(sf));
> +	util_clamp = tg->uclamp_req[clamp_id].value;
> +	rcu_read_unlock();
Why is the rcu_read_lock() needed here? (I'm considering the comment in
of_css() that should apply here (and it seems that similar uses in other
seq_file handlers also skip this).)

> @@ -7369,6 +7506,20 @@ static struct cftype cpu_legacy_files[] = {
> [...]
> +		.name = "uclamp.min",
> [...]
> +		.name = "uclamp.max",
I don't see technical reasons why uclamp couldn't work on legacy
hierarchy and Tejun acked the series, despite that I'll ask -- should
the new attributes be exposed in v1 controller hierarchy (taking into
account the legacy API is sort of frozen and potential maintenance needs
spanning both hierarchies)?


^ permalink raw reply	[flat|nested] 15+ messages in thread

* Re: [PATCH v13 2/6] sched/core: uclamp: Propagate parent clamps
  2019-08-02  9:08 ` [PATCH v13 2/6] sched/core: uclamp: Propagate parent clamps Patrick Bellasi
@ 2019-08-06 16:11   ` Michal Koutný
  2019-08-08 15:08     ` Patrick Bellasi
  0 siblings, 1 reply; 15+ messages in thread
From: Michal Koutný @ 2019-08-06 16:11 UTC (permalink / raw)
  To: Patrick Bellasi
  Cc: linux-kernel, linux-pm, linux-api, cgroups, 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

[-- Attachment #1: Type: text/plain, Size: 932 bytes --]

On Fri, Aug 02, 2019 at 10:08:49AM +0100, Patrick Bellasi <patrick.bellasi@arm.com> wrote:
> @@ -7095,6 +7149,7 @@ static ssize_t cpu_uclamp_write(struct kernfs_open_file *of, char *buf,
>  	if (req.ret)
>  		return req.ret;
>  
> +	mutex_lock(&uclamp_mutex);
>  	rcu_read_lock();
>  
>  	tg = css_tg(of_css(of));
> @@ -7107,7 +7162,11 @@ static ssize_t cpu_uclamp_write(struct kernfs_open_file *of, char *buf,
>  	 */
>  	tg->uclamp_pct[clamp_id] = req.percent;
>  
> +	/* Update effective clamps to track the most restrictive value */
> +	cpu_util_update_eff(of_css(of));
> +
>  	rcu_read_unlock();
> +	mutex_unlock(&uclamp_mutex);
Following my remarks to "[PATCH v13 1/6] sched/core: uclamp: Extend
CPU's cgroup", I wonder if the rcu_read_lock() couldn't be moved right
before cpu_util_update_eff(). And by extension rcu_read_(un)lock could
be hidden into cpu_util_update_eff() closer to its actual need.


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^ permalink raw reply	[flat|nested] 15+ messages in thread

* Re: [PATCH v13 0/6] Add utilization clamping support (CGroups API)
  2019-08-02  9:08 [PATCH v13 0/6] Add utilization clamping support (CGroups API) Patrick Bellasi
                   ` (5 preceding siblings ...)
  2019-08-02  9:08 ` [PATCH v13 6/6] sched/core: uclamp: always use enum uclamp_id for clamp_id values Patrick Bellasi
@ 2019-08-06 16:12 ` Michal Koutný
  2019-08-06 16:40   ` Patrick Bellasi
  6 siblings, 1 reply; 15+ messages in thread
From: Michal Koutný @ 2019-08-06 16:12 UTC (permalink / raw)
  To: Patrick Bellasi
  Cc: linux-kernel, linux-pm, linux-api, cgroups, 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

[-- Attachment #1: Type: text/plain, Size: 750 bytes --]

On Fri, Aug 02, 2019 at 10:08:47AM +0100, Patrick Bellasi <patrick.bellasi@arm.com> wrote:
> Patrick Bellasi (6):
>   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
>   sched/core: uclamp: always use enum uclamp_id for clamp_id values
Thank you Patrick for your patience. I used the time to revisit the
series once again and I think the RCU locks can be streamlined a bit. If
you find that correct, feel free to add my Reviewed-by to the updated
series (for 1/6 and legacy, I'm just asking).

Michal

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^ permalink raw reply	[flat|nested] 15+ messages in thread

* Re: [PATCH v13 0/6] Add utilization clamping support (CGroups API)
  2019-08-06 16:12 ` [PATCH v13 0/6] Add utilization clamping support (CGroups API) Michal Koutný
@ 2019-08-06 16:40   ` Patrick Bellasi
  0 siblings, 0 replies; 15+ messages in thread
From: Patrick Bellasi @ 2019-08-06 16:40 UTC (permalink / raw)
  To: Michal Koutný
  Cc: linux-kernel, linux-pm, linux-api, cgroups, 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 Tue, Aug 06, 2019 at 17:12:06 +0100, Michal Koutný wrote...

> On Fri, Aug 02, 2019 at 10:08:47AM +0100, Patrick Bellasi <patrick.bellasi@arm.com> wrote:
>> Patrick Bellasi (6):
>>   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
>>   sched/core: uclamp: always use enum uclamp_id for clamp_id values

Hi Michal!

> Thank you Patrick for your patience.

Thanks to you for your reviews.

> I used the time to revisit the series once again and I think the RCU
> locks can be streamlined a bit.

I'll have a look at those, thanks!

> If you find that correct, feel free to add my Reviewed-by to the
> updated series (for 1/6 and legacy, I'm just asking).

Sure, actually sorry for not having already added that tag in the
current version, it will be there in v14 ;)

> Michal

Cheers,
Patrick

--
#include <best/regards.h>

Patrick Bellasi


^ permalink raw reply	[flat|nested] 15+ messages in thread

* Re: [PATCH v13 2/6] sched/core: uclamp: Propagate parent clamps
  2019-08-06 16:11   ` Michal Koutný
@ 2019-08-08 15:08     ` Patrick Bellasi
  2019-08-08 17:16       ` Michal Koutný
  0 siblings, 1 reply; 15+ messages in thread
From: Patrick Bellasi @ 2019-08-08 15:08 UTC (permalink / raw)
  To: Michal Koutný
  Cc: linux-kernel, linux-pm, linux-api, cgroups, 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 Tue, Aug 06, 2019 at 17:11:53 +0100, Michal Koutný wrote...

> On Fri, Aug 02, 2019 at 10:08:49AM +0100, Patrick Bellasi <patrick.bellasi@arm.com> wrote:
>> @@ -7095,6 +7149,7 @@ static ssize_t cpu_uclamp_write(struct kernfs_open_file *of, char *buf,
>>  	if (req.ret)
>>  		return req.ret;
>>  
>> +	mutex_lock(&uclamp_mutex);
>>  	rcu_read_lock();
>>  
>>  	tg = css_tg(of_css(of));
>> @@ -7107,7 +7162,11 @@ static ssize_t cpu_uclamp_write(struct kernfs_open_file *of, char *buf,
>>  	 */
>>  	tg->uclamp_pct[clamp_id] = req.percent;
>>  
>> +	/* Update effective clamps to track the most restrictive value */
>> +	cpu_util_update_eff(of_css(of));
>> +
>>  	rcu_read_unlock();
>> +	mutex_unlock(&uclamp_mutex);
> Following my remarks to "[PATCH v13 1/6] sched/core: uclamp: Extend
> CPU's cgroup", I wonder if the rcu_read_lock() couldn't be moved right
> before cpu_util_update_eff(). And by extension rcu_read_(un)lock could
> be hidden into cpu_util_update_eff() closer to its actual need.

Well, if I've got correctly your comment in the previous message, I
would say that at this stage we don't need RCU looks at all.

Reason being that cpu_util_update_eff() gets called only from
cpu_uclamp_write() which is from an ongoing write operation on a cgroup
attribute and thus granted to be available.

We will eventually need to move the RCU look only down the stack when
uclamp_update_active_tasks() gets called to update the RUNNABLE tasks on
a RQ... or perhaps we don't need them since we already get the
task_rq_lock() for each task we visit.

Is that correct?

Cheers,
Patrick

-- 
#include <best/regards.h>

Patrick Bellasi

^ permalink raw reply	[flat|nested] 15+ messages in thread

* Re: [PATCH v13 1/6] sched/core: uclamp: Extend CPU's cgroup controller
  2019-08-06 16:11   ` Michal Koutný
@ 2019-08-08 15:10     ` Patrick Bellasi
  2019-08-08 17:19       ` Michal Koutný
  0 siblings, 1 reply; 15+ messages in thread
From: Patrick Bellasi @ 2019-08-08 15:10 UTC (permalink / raw)
  To: Michal Koutný
  Cc: linux-kernel, linux-pm, linux-api, cgroups, 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 Tue, Aug 06, 2019 at 17:11:34 +0100, Michal Koutný wrote...

> On Fri, Aug 02, 2019 at 10:08:48AM +0100, Patrick Bellasi <patrick.bellasi@arm.com> wrote:
>> +static ssize_t cpu_uclamp_write(struct kernfs_open_file *of, char *buf,
>> +				size_t nbytes, loff_t off,
>> +				enum uclamp_id clamp_id)
>> +{
>> +	struct uclamp_request req;
>> +	struct task_group *tg;
>> +
>> +	req = capacity_from_percent(buf);
>> +	if (req.ret)
>> +		return req.ret;
>> +
>> +	rcu_read_lock();
> This should be the uclamp_mutex.
>
> (The compound results of the series is correct as the lock is introduced
> in "sched/core: uclamp: Propagate parent clamps".
> This is just for the happiness of cherry-pickers/bisectors.)

Right, will move the uclamp_mutex introduction in this patch instead of
in the following one.

>> +static inline void cpu_uclamp_print(struct seq_file *sf,
>> +				    enum uclamp_id clamp_id)
>> +{
>> [...]
>> +	rcu_read_lock();
>> +	tg = css_tg(seq_css(sf));
>> +	util_clamp = tg->uclamp_req[clamp_id].value;
>> +	rcu_read_unlock();
> Why is the rcu_read_lock() needed here? (I'm considering the comment in
> of_css() that should apply here (and it seems that similar uses in other
> seq_file handlers also skip this).)

So, looks like that since we are in the context of a file operation,
all the cgroup's attribute read/write functions are implicitly save.

IOW, we don't need an RCU lock since the TG data structures are granted
to be always available till the end of the read/write operation.

That seems to make sense... I'm wondering if keeping the RCU look is
still a precaution for possible future code/assumption changes or just
an unnecessary overhead?

>> @@ -7369,6 +7506,20 @@ static struct cftype cpu_legacy_files[] = {
>> [...]
>> +		.name = "uclamp.min",
>> [...]
>> +		.name = "uclamp.max",
> I don't see technical reasons why uclamp couldn't work on legacy
> hierarchy and Tejun acked the series, despite that I'll ask -- should
> the new attributes be exposed in v1 controller hierarchy (taking into
> account the legacy API is sort of frozen and potential maintenance needs
> spanning both hierarchies)?

Not sure to get what you mean here: I'm currently exposing uclamp to
both v1 and v2 hierarchies.

Best,
Patrick

--
#include <best/regards.h>

Patrick Bellasi

^ permalink raw reply	[flat|nested] 15+ messages in thread

* Re: [PATCH v13 2/6] sched/core: uclamp: Propagate parent clamps
  2019-08-08 15:08     ` Patrick Bellasi
@ 2019-08-08 17:16       ` Michal Koutný
  0 siblings, 0 replies; 15+ messages in thread
From: Michal Koutný @ 2019-08-08 17:16 UTC (permalink / raw)
  To: Patrick Bellasi
  Cc: Alessio Balsini, Dietmar Eggemann, Morten Rasmussen,
	Quentin Perret, Joel Fernandes, Paul Turner, Steve Muckle,
	Suren Baghdasaryan, Todd Kjos, Peter Zijlstra,
	Rafael J . Wysocki, Tejun Heo, VincentGuittot, Viresh Kumar,
	Juri Lelli, Ingo Molnar, cgroups, linux-api, linux-kernel,
	linux-pm

[-- Attachment #1: Type: text/plain, Size: 883 bytes --]

On Thu, Aug 08, 2019 at 04:08:10PM +0100, Patrick Bellasi <patrick.bellasi@arm.com> wrote:
> Well, if I've got correctly your comment in the previous message, I
> would say that at this stage we don't need RCU looks at all.
Agreed.

> Reason being that cpu_util_update_eff() gets called only from
> cpu_uclamp_write() which is from an ongoing write operation on a cgroup
> attribute and thus granted to be available.
> 
> We will eventually need to move the RCU look only down the stack when
> uclamp_update_active_tasks() gets called to update the RUNNABLE tasks on
> a RQ... or perhaps we don't need them since we already get the
> task_rq_lock() for each task we visit.
Unless you remove css_for_each_descendant_pre() in
cpu_util_update_eff(), the rcu_read_lock() cannot go below it.
(You'd be RCU-accessing other csses that aren't pinned in the write.)

Michal

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^ permalink raw reply	[flat|nested] 15+ messages in thread

* Re: [PATCH v13 1/6] sched/core: uclamp: Extend CPU's cgroup controller
  2019-08-08 15:10     ` Patrick Bellasi
@ 2019-08-08 17:19       ` Michal Koutný
  0 siblings, 0 replies; 15+ messages in thread
From: Michal Koutný @ 2019-08-08 17:19 UTC (permalink / raw)
  To: Patrick Bellasi
  Cc: Alessio Balsini, Dietmar Eggemann, Morten Rasmussen,
	Quentin Perret, Joel Fernandes, Paul Turner, Steve Muckle,
	Suren Baghdasaryan, Todd Kjos, Peter Zijlstra,
	Rafael J . Wysocki, Tejun Heo, VincentGuittot, Viresh Kumar,
	Juri Lelli, Ingo Molnar, cgroups, linux-api, linux-kernel,
	linux-pm

[-- Attachment #1: Type: text/plain, Size: 359 bytes --]

On Thu, Aug 08, 2019 at 04:10:21PM +0100, Patrick Bellasi <patrick.bellasi@arm.com> wrote:
> Not sure to get what you mean here: I'm currently exposing uclamp to
> both v1 and v2 hierarchies.
cpu controller has different API for v1 and v2 hierarchies. My question
reworded is -- are the new knobs exposed in the legacy API
intentionally/for a reason?

Michal

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^ permalink raw reply	[flat|nested] 15+ messages in thread

end of thread, other threads:[~2019-08-08 17:19 UTC | newest]

Thread overview: 15+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2019-08-02  9:08 [PATCH v13 0/6] Add utilization clamping support (CGroups API) Patrick Bellasi
2019-08-02  9:08 ` [PATCH v13 1/6] sched/core: uclamp: Extend CPU's cgroup controller Patrick Bellasi
2019-08-06 16:11   ` Michal Koutný
2019-08-08 15:10     ` Patrick Bellasi
2019-08-08 17:19       ` Michal Koutný
2019-08-02  9:08 ` [PATCH v13 2/6] sched/core: uclamp: Propagate parent clamps Patrick Bellasi
2019-08-06 16:11   ` Michal Koutný
2019-08-08 15:08     ` Patrick Bellasi
2019-08-08 17:16       ` Michal Koutný
2019-08-02  9:08 ` [PATCH v13 3/6] sched/core: uclamp: Propagate system defaults to root group Patrick Bellasi
2019-08-02  9:08 ` [PATCH v13 4/6] sched/core: uclamp: Use TG's clamps to restrict TASK's clamps Patrick Bellasi
2019-08-02  9:08 ` [PATCH v13 5/6] sched/core: uclamp: Update CPU's refcount on TG's clamp changes Patrick Bellasi
2019-08-02  9:08 ` [PATCH v13 6/6] sched/core: uclamp: always use enum uclamp_id for clamp_id values Patrick Bellasi
2019-08-06 16:12 ` [PATCH v13 0/6] Add utilization clamping support (CGroups API) Michal Koutný
2019-08-06 16:40   ` Patrick Bellasi

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