Message-ID: <Y3II59dyKuvQGIhG@debian.me>
Date:   Mon, 14 Nov 2022 16:22:47 +0700
From:   Bagas Sanjaya <bagasdotme@...il.com>
To:     Qais Yousef <qyousef@...alina.io>
Cc:     Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        linux-kernel@...r.kernel.org, Lukasz Luba <lukasz.luba@....com>,
        Xuewen Yan <xuewen.yan94@...il.com>, Wei Wang <wvw@...gle.com>,
        Jonathan JMChen <Jonathan.JMChen@...iatek.com>,
        Hank <han.lin@...iatek.com>, Paul Bone <pbone@...illa.com>
Subject: Re: [PATCH] Documentation: sched: Add a new sched-util-clamp.rst

On Sat, Nov 05, 2022 at 11:23:43PM +0000, Qais Yousef wrote:
> +2.  DESIGN:
> +===========

Why ALLCAPS and trailing colon for section title?

> +When a task is attached to a CPU controller, its uclamp values will be impacted
> +as follows:
> +
> +* cpu.uclamp.min is a protection as described in section 3-3 in
> +  Documentation/admin-guide/cgroup-v2.rst.
> <snipped>...
> +* cpu.uclamp.max is a limit as described in section 3-2 in
> +  Documentation/admin-guide/cgroup-v2.rst.
> +

Exactly what section on cgroup doc do you refer? I don't see any section
number there. Did you mean this?:

---- >8 ----

diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst
index dc254a3cb95686..fd448069c11562 100644
--- a/Documentation/admin-guide/cgroup-v2.rst
+++ b/Documentation/admin-guide/cgroup-v2.rst
@@ -619,6 +619,8 @@ process migrations.
 and is an example of this type.
 
 
+.. _cgroupv2-limits-distributor:
+
 Limits
 ------
 
@@ -635,6 +637,7 @@ process migrations.
 "io.max" limits the maximum BPS and/or IOPS that a cgroup can consume
 on an IO device and is an example of this type.
 
+.. _cgroupv2-protections-distributor:
 
 Protections
 -----------
diff --git a/Documentation/scheduler/sched-util-clamp.rst b/Documentation/scheduler/sched-util-clamp.rst
index 6601bda176d16e..5741acb35b7db2 100644
--- a/Documentation/scheduler/sched-util-clamp.rst
+++ b/Documentation/scheduler/sched-util-clamp.rst
@@ -364,8 +364,8 @@ There are two uclamp related values in the CPU cgroup controller:
 When a task is attached to a CPU controller, its uclamp values will be impacted
 as follows:
 
-* cpu.uclamp.min is a protection as described in section 3-3 in
-  Documentation/admin-guide/cgroup-v2.rst.
+* cpu.uclamp.min is a protection as described in :ref:`section 3-3 of cgroup
+  v2 documentation <cgroupv2-protections-distributor>`.
 
   If a task uclamp_min value is lower than cpu.uclamp.min, then the task will
   inherit the cgroup cpu.uclamp.min value.
@@ -373,8 +373,8 @@ as follows:
   In a cgroup hierarchy, effective cpu.uclamp.min is the max of (child,
   parent).
 
-* cpu.uclamp.max is a limit as described in section 3-2 in
-  Documentation/admin-guide/cgroup-v2.rst.
+* cpu.uclamp.max is a limit as described in :ref:`section 3-2 of cgroup v2
+  documentation <cgroupv2-limits-distributor>`.
 
   If a task uclamp_max value is higher than cpu.uclamp.max, then the task will
   inherit the cgroup cpu.uclamp.max value.


IMO, the doc wording can be improved (applied on top of your fixup [1]):

---- >8 ----

diff --git a/Documentation/scheduler/sched-util-clamp.rst b/Documentation/scheduler/sched-util-clamp.rst
index 728ffa364fc7ad..6601bda176d16e 100644
--- a/Documentation/scheduler/sched-util-clamp.rst
+++ b/Documentation/scheduler/sched-util-clamp.rst
@@ -2,31 +2,29 @@
 Utilization Clamping
 ====================
 
-1.  INTRODUCTION
-================
+1. Introduction
+===============
 
-Utilization clamping is a scheduler feature that allows user space to help in
-managing the performance requirement of tasks. It was introduced in v5.3
-release. The CGroup support was merged in v5.4.
-
-It is often referred to as util clamp and uclamp. You'll find all variations
-used interchangeably in this documentation and in the source code.
+Utilization clamping, also known as util clamp or uclamp, is a scheduler
+feature that allows user space to help in managing the performance requirement
+of tasks. It was introduced in v5.3 release. The CGroup support was merged in
+v5.4.
 
 Uclamp is a hinting mechanism that allows the scheduler to understand the
-performance requirements and restrictions of the tasks. Hence help it make
-a better placement decision. And when schedutil cpufreq governor is used, util
-clamp will influence the frequency selection as well.
+performance requirements and restrictions of the tasks, thus it helps the
+scheduler to make a better decision. And when schedutil cpufreq governor is
+used, util clamp will influence the frequency selection as well.
 
 Since scheduler and schedutil are both driven by PELT (util_avg) signals, util
 clamp acts on that to achieve its goal by clamping the signal to a certain
-point; hence the name. I.e: by clamping utilization we are making the system
-run at a certain performance point.
+point; hence the name. That is, by clamping utilization we are making the
+system run at a certain performance point.
 
-The right way to view util clamp is as a mechanism to make performance
-constraints request/hint. It consists of two components:
+The right way to view util clamp is as a mechanism to make request or hint on
+performance constraints. It consists of two tunables:
 
-        * UCLAMP_MIN, which sets a lower bound.
-        * UCLAMP_MAX, which sets an upper bound.
+        * UCLAMP_MIN, which sets the lower bound.
+        * UCLAMP_MAX, which sets the upper bound.
 
 These two bounds will ensure a task will operate within this performance range
 of the system. UCLAMP_MIN implies boosting a task, while UCLAMP_MAX implies
@@ -35,18 +33,18 @@ capping a task.
 One can tell the system (scheduler) that some tasks require a minimum
 performance point to operate at to deliver the desired user experience. Or one
 can tell the system that some tasks should be restricted from consuming too
-much resources and should NOT go above a specific performance point. Viewing
+much resources and should not go above a specific performance point. Viewing
 the uclamp values as performance points rather than utilization is a better
 abstraction from user space point of view.
 
 As an example, a game can use util clamp to form a feedback loop with its
 perceived FPS. It can dynamically increase the minimum performance point
 required by its display pipeline to ensure no frame is dropped. It can also
-dynamically 'prime' up these tasks if it knows in the coming few 100ms
-a computationally intensive scene is about to happen.
+dynamically 'prime' up these tasks if it knows in the coming few hundred
+milliseconds a computationally intensive scene is about to happen.
 
 On mobile hardware where the capability of the devices varies a lot, this
-dynamic feedback loop offers a great flexibility in ensuring best user
+dynamic feedback loop offers a great flexibility to ensure best user
 experience given the capabilities of any system.
 
 Of course a static configuration is possible too. The exact usage will depend
@@ -68,17 +66,17 @@ stay on the little cores which will ensure that:
            are CPU intensive tasks.
 
 By making these uclamp performance requests, or rather hints, user space can
-ensure system resources are used optimally to deliver the best user experience
-the system is capable of.
+ensure system resources are used optimally to deliver the best possible user
+experience.
 
 Another use case is to help with overcoming the ramp up latency inherit in how
 scheduler utilization signal is calculated.
 
-A busy task for instance that requires to run at maximum performance point will
-suffer a delay of ~200ms (PELT HALFIFE = 32ms) for the scheduler to realize
-that. This is known to affect workloads like gaming on mobile devices where
-frames will drop due to slow response time to select the higher frequency
-required for the tasks to finish their work in time.
+On the other hand, a busy task for instance that requires to run at maximum
+performance point will suffer a delay of ~200ms (PELT HALFIFE = 32ms) for the
+scheduler to realize that. This is known to affect workloads like gaming on
+mobile devices where frames will drop due to slow response time to select the
+higher frequency required for the tasks to finish their work in time.
 
 The overall visible effect goes beyond better perceived user
 experience/performance and stretches to help achieve a better overall
@@ -101,11 +99,12 @@ when an RT task wakes up. This cost is unchanged by using uclamp. Uclamp only
 helps picking what frequency to request instead of schedutil always requesting
 MAX for all RT tasks.
 
-See section 3.4 for default values and 3.4.1 on how to change RT tasks default
-value.
+See :ref:`section 3.4 <uclamp-default-values>` for default values and
+:ref:`3.4.1 <sched-util-clamp-min-rt-default>` on how to change RT tasks
+default value.
 
-2.  DESIGN:
-===========
+2. Design
+=========
 
 Util clamp is a property of every task in the system. It sets the boundaries of
 its utilization signal; acting as a bias mechanism that influences certain
@@ -123,10 +122,10 @@ which have implications on the utilization value at rq level, which brings us
 to the main design challenge.
 
 When a task wakes up on an rq, the utilization signal of the rq will be
-impacted by the uclamp settings of all the tasks enqueued on it. For example if
+affected by the uclamp settings of all the tasks enqueued on it. For example if
 a task requests to run at UTIL_MIN = 512, then the util signal of the rq needs
-to respect this request as well as all other requests from all of the enqueued
-tasks.
+to respect to this request as well as all other requests from all of the
+enqueued tasks.
 
 To be able to aggregate the util clamp value of all the tasks attached to the
 rq, uclamp must do some housekeeping at every enqueue/dequeue, which is the
@@ -138,19 +137,21 @@ The way this is handled is by dividing the utilization range into buckets
 (struct uclamp_bucket) which allows us to reduce the search space from every
 task on the rq to only a subset of tasks on the top-most bucket.
 
-When a task is enqueued, we increment a counter in the matching bucket. And on
-dequeue we decrement it. This makes keeping track of the effective uclamp value
-at rq level a lot easier.
+When a task is enqueued, the counter in the matching bucket is incremented,
+and on dequeue it is decremented. This makes keeping track of the effective
+uclamp value at rq level a lot easier.
 
-As we enqueue and dequeue tasks we keep track of the current effective uclamp
-value of the rq. See section 2.1 for details on how this works.
+As tasks are enqueued and dequeued, we keep track of the current effective
+uclamp value of the rq. See :ref:`section 2.1 <uclamp-buckets>` for details on
+how this works.
 
 Later at any path that wants to identify the effective uclamp value of the rq,
 it will simply need to read this effective uclamp value of the rq at that exact
 moment of time it needs to take a decision.
 
 For task placement case, only Energy Aware and Capacity Aware Scheduling
-(EAS/CAS) make use of uclamp for now. This implies heterogeneous systems only.
+(EAS/CAS) make use of uclamp for now, which implies that it is applied on
+heterogeneous systems only.
 When a task wakes up, the scheduler will look at the current effective uclamp
 value of every rq and compare it with the potential new value if the task were
 to be enqueued there. Favoring the rq that will end up with the most energy
@@ -159,17 +160,19 @@ efficient combination.
 Similarly in schedutil, when it needs to make a frequency update it will look
 at the current effective uclamp value of the rq which is influenced by the set
 of tasks currently enqueued there and select the appropriate frequency that
-will honour uclamp requests.
+will satisfy constraints from requests.
 
 Other paths like setting overutilization state (which effectively disables EAS)
 make use of uclamp as well. Such cases are considered necessary housekeeping to
 allow the 2 main use cases above and will not be covered in detail here as they
 could change with implementation details.
 
-2.1  BUCKETS:
--------------
+.. _uclamp-buckets:
 
-.. code-block:: c
+2.1. Buckets
+------------
+
+.. code-block::
 
                            [struct rq]
 
@@ -189,7 +192,6 @@ could change with implementation details.
 
 
 .. note::
-  DISCLAMER:
    The diagram above is an illustration rather than a true depiction of the
    internal data structure.
 
@@ -198,12 +200,11 @@ an rq as tasks are enqueued/dequeued, the whole utilization range is divided
 into N buckets where N is configured at compile time by setting
 CONFIG_UCLAMP_BUCKETS_COUNT. By default it is set to 5.
 
-The rq has a bucket for each uclamp_id: [UCLAMP_MIN, UCLAMP_MAX].
+The rq has a bucket for each uclamp_id tunables: [UCLAMP_MIN, UCLAMP_MAX].
 
-The range of each bucket is 1024/N. For example for the default value of 5 we
-will have 5 buckets, each of which will cover the following range:
+The range of each bucket is 1024/N. For example, for the default value of 5 there will be 5 buckets, each of which will cover the following range:
 
-.. code-block:: c
+.. code-block::
 
         DELTA = round_closest(1024/5) = 204.8 = 205
 
@@ -213,21 +214,21 @@ will have 5 buckets, each of which will cover the following range:
         Bucket 3: [615:819]
         Bucket 4: [820:1024]
 
-When a task p
+When a task p with following tunable parameters
 
 .. code-block:: c
 
         p->uclamp[UCLAMP_MIN] = 300
         p->uclamp[UCLAMP_MAX] = 1024
 
-is enqueued into the rq, Bucket 1 will be incremented for UCLAMP_MIN and Bucket
+is enqueued into the rq, bucket 1 will be incremented for UCLAMP_MIN and bucket
 4 will be incremented for UCLAMP_MAX to reflect the fact the rq has a task in
 this range.
 
 The rq then keeps track of its current effective uclamp value for each
 uclamp_id.
 
-When a task p is enqueued, the rq value changes as follows:
+When a task p is enqueued, the rq value changes to:
 
 .. code-block:: c
 
@@ -235,7 +236,7 @@ When a task p is enqueued, the rq value changes as follows:
         rq->uclamp[UCLAMP_MIN] = max(rq->uclamp[UCLAMP_MIN], p->uclamp[UCLAMP_MIN])
         // repeat for UCLAMP_MAX
 
-When a task is p dequeued the rq value changes as follows:
+Similarly, when p is dequeued the rq value changes to:
 
 .. code-block:: c
 
@@ -244,11 +245,11 @@ When a task is p dequeued the rq value changes as follows:
         // repeat for UCLAMP_MAX
 
 When all buckets are empty, the rq uclamp values are reset to system defaults.
-See section 3.4 for default values.
+See :ref:`section 3.4 <uclamp-default-values>` for details on default values.
 
 
-2.2  MAX AGGREGATION:
----------------------
+2.2. Max aggregation
+--------------------
 
 Util clamp is tuned to honour the request for the task that requires the
 highest performance point.
@@ -268,19 +269,20 @@ values:
         p1->uclamp[UCLAMP_MIN] = 500
         p1->uclamp[UCLAMP_MAX] = 500
 
-then assuming both p0 and p1 are enqueued to the same rq
+then assuming both p0 and p1 are enqueued to the same rq, both UCLAMP_MIN
+and UCLAMP_MAX become:
 
 .. code-block:: c
 
         rq->uclamp[UCLAMP_MIN] = max(300, 500) = 500
         rq->uclamp[UCLAMP_MAX] = max(900, 500) = 900
 
-As we shall see in section 5.1, this max aggregation is the cause of one of the
-limitations when using util clamp. Particularly for UCLAMP_MAX hint when user
-space would like to save power.
+As we shall see in :ref:`section 5.1 <uclamp-capping-fail>`, this max
+aggregation is the cause of one of limitations when using util clamp, in
+particular for UCLAMP_MAX hint when user space would like to save power.
 
-2.3  HIERARCHICAL AGGREGATION:
-------------------------------
+2.3. Hierarchial aggregation
+----------------------------
 
 As stated earlier, util clamp is a property of every task in the system. But
 the actual applied (effective) value can be influenced by more than just the
@@ -293,80 +295,66 @@ The effective util clamp value of any task is restricted as follows:
   2. The restricted value in (1) is then further restricted by the system wide
      uclamp settings.
 
-Section 3 discusses the interfaces and will expand further on that.
+:ref:`Section 3 <uclamp-interfaces>` discusses the interfaces and will expand further on that.
 
 For now suffice to say that if a task makes a request, its actual effective
 value will have to adhere to some restrictions imposed by cgroup and system
 wide settings.
 
-The system will still accept the request even if effectively will look
-different; but as soon as the task moves to a different cgroup or a sysadmin
-modifies the system settings, it'll be able to get what it wants if the new
-settings allows it.
+The system will still accept the request even if effectively will be
+beyond the constraints, but as soon as the task moves to a different cgroup
+or a sysadmin modifies the system settings, the request will be satisfied
+only if it is within new constraints.
 
 In other words, this aggregation will not cause an error when a task changes
-its uclamp values. It just might not be able to achieve it based on those
-factors.
+its uclamp values, but rather the system may not be able to satisfy requests
+based on those factors.
 
 2.4  Range:
 -----------
 
-Uclamp performance request follow the utilization range: [0:1024] inclusive.
+Uclamp performance request has the range of 0 to 1024 inclusive.
 
-For cgroup interface percentage is used: [0:100] inclusive.
-You can use 'max' instead of 100 like other cgroup interfaces.
+For cgroup interface percentage is used (that is 0 to 100 inclusive).
+Just like other cgroup interfaces, you can use 'max' instead of 100.
 
-3.  INTERFACES:
-===============
+.. _uclamp-interfaces:
 
-3.1  PER TASK INTERFACE:
-------------------------
+3.  Interfaces
+==============
+
+3.1  Per-task interface
+-----------------------
 
 sched_setattr() syscall was extended to accept two new fields:
 
 * sched_util_min: requests the minimum performance point the system should run
-                  at when this task is running. Or lower performance bound.
+  at when this task is running. Or lower performance bound.
 * sched_util_max: requests the maximum performance point the system should run
-                  at when this task is running. Or upper performance bound.
+  at when this task is running. Or upper performance bound.
 
-For example:
+For example, the following scenario have 40% to 80% utilization constraints:
 
 .. code-block:: c
 
         attr->sched_util_min = 40% * 1024;
         attr->sched_util_max = 80% * 1024;
 
-Will tell the system that when task @p is running, it should try its best to
-ensure it starts at a performance point no less than 40% of maximum system's
-capability.
-
-And if the task runs for a long enough time so that its actual utilization goes
-above 80%, then it should not cause the system to operate at a performance
-point higher than that.
+When task @p is running, the scheduler should try its best to ensure it starts
+at 40% utilization. If the task runs for a long enough time so that its actual
+utilization goes above 80%, the utilization will be capped.
 
 The special value -1 is used to reset the uclamp settings to the system
 default.
 
 Note that resetting the uclamp value to system default using -1 is not the same
-as setting the uclamp value to system default.
+as manually setting uclamp value to system default. This distinction is
+important because as we shall see in system interfaces, the default value for
+RT could be changed. SCHED_NORMAL/OTHER might gain similar knobs too in the
+future.
 
-.. code-block:: c
-
-        attr->sched_util_min = -1  // p0 is reset to system default e.g: 0
-
-not the same as
-
-.. code-block:: c
-
-        attr->sched_util_min = 0   // p0 is set to 0, the fact it is the same
-                                   // as system default is irrelevant
-
-This distinction is important because as we shall see in system interfaces, the
-default value for RT could be changed. SCHED_NORMAL/OTHER might gain similar
-knobs too in the future.
-
-3.2  CGROUP INTERFACE:
-----------------------
+3.2. cgroup interface
+---------------------
 
 There are two uclamp related values in the CPU cgroup controller:
 
@@ -394,7 +382,7 @@ as follows:
   In a cgroup hierarchy, effective cpu.uclamp.max is the min of (child,
   parent).
 
-For example:
+For example, given following parameters:
 
 .. code-block:: c
 
@@ -410,7 +398,7 @@ For example:
         cgroup1->cpu.uclamp.min = 60% * 1024;
         cgroup1->cpu.uclamp.max = 100% * 1024;
 
-when p0 and p1 are attached to cgroup0
+when p0 and p1 are attached to cgroup0, the values become:
 
 .. code-block:: c
 
@@ -420,7 +408,7 @@ when p0 and p1 are attached to cgroup0
         p1->uclamp[UCLAMP_MIN] = 40% * 1024; // intact
         p1->uclamp[UCLAMP_MAX] = 50% * 1024; // intact
 
-when p0 and p1 are attached to cgroup1
+when p0 and p1 are attached to cgroup1, these instead become:
 
 .. code-block:: c
 
@@ -433,49 +421,46 @@ when p0 and p1 are attached to cgroup1
 Note that cgroup interfaces allows cpu.uclamp.max value to be lower than
 cpu.uclamp.min. Other interfaces don't allow that.
 
-3.3  SYSTEM INTERFACE:
+3.3.  System interface
 ----------------------
 
-3.3.1  sched_util_clamp_min:
-----------------------------
+3.3.1  sched_util_clamp_min
+---------------------------
 
-System wide limit of allowed UCLAMP_MIN range. By default set to 1024, which
-means tasks are allowed to reach an effective UCLAMP_MIN value in the range of
-[0:1024].
+System wide limit of allowed UCLAMP_MIN range. By default it is set to 1024,
+which means that permitted effective UCLAMP_MIN range for tasks is [0:1024].
+By changing it to 512 for example the range reduces to [0:512]. This is useful
+to restrict how much boosting tasks are allowed to acquire.
 
-By changing it to 512 for example the effective allowed range reduces to
-[0:512].
-
-This is useful to restrict how much boosting tasks are allowed to acquire.
-
-Requests from tasks to go above this point will still succeed, but effectively
-they won't be achieved until this value is >= p->uclamp[UCLAMP_MIN].
+Requests from tasks to go above this knob value will still succeed, but
+they won't be satisfied until it is more than p->uclamp[UCLAMP_MIN].
 
 The value must be smaller than or equal to sched_util_clamp_max.
 
-3.3.2  sched_util_clamp_max:
-----------------------------
+3.3.2  sched_util_clamp_max
+---------------------------
 
-System wide limit of allowed UCLAMP_MAX range. By default set to 1024, which
-means tasks are allowed to reach an effective UCLAMP_MAX value in the range of
-[0:1024].
+System wide limit of allowed UCLAMP_MAX range. By default it is set to 1024,
+which means that permitted effective UCLAMP_MAX range for tasks is [0:1024].
 
 By changing it to 512 for example the effective allowed range reduces to
-[0:512]. The visible impact of this is that no task can run above 512, which in
-return means that all rqs are restricted too. IOW, the whole system is capped
-to half its performance capacity.
+[0:512]. This means is that no task can run above 512, which implies that all
+rqs are restricted too. IOW, the whole system is capped to half its performance
+capacity.
 
-This is useful to restrict the overall maximum performance point of the system.
+This is useful to restrict the overall maximum performance point of the
+system. For example, it can be handy to limit performance when running low on
+battery.
 
-Can be handy to limit performance when running low on battery.
-
-Requests from tasks to go above this point will still succeed, but effectively
-they won't be achieved until this value is >= p->uclamp[UCLAMP_MAX].
+Requests from tasks to go above this knob value will still succeed, but
+they won't be satisfied until it is more than p->uclamp[UCLAMP_MAX].
 
 The value must be greater than or equal to sched_util_clamp_min.
 
-3.4  DEFAULT VALUES:
-----------------------
+.. _uclamp-default-values:
+
+3.4. Default values
+-------------------
 
 By default all SCHED_NORMAL/SCHED_OTHER tasks are initialized to:
 
@@ -484,7 +469,7 @@ By default all SCHED_NORMAL/SCHED_OTHER tasks are initialized to:
         p_fair->uclamp[UCLAMP_MIN] = 0
         p_fair->uclamp[UCLAMP_MAX] = 1024
 
-That is no boosting or restriction on any task. These default values can't be
+That is, no boosting or restriction on any task. These default values can't be
 changed at boot or runtime. No argument was made yet as to why we should
 provide this, but can be added in the future.
 
@@ -495,33 +480,35 @@ For SCHED_FIFO/SCHED_RR tasks:
         p_rt->uclamp[UCLAMP_MIN] = 1024
         p_rt->uclamp[UCLAMP_MAX] = 1024
 
-That is by default they're boosted to run at the maximum performance point of
+That is, by default they're boosted to run at the maximum performance point of
 the system which retains the historical behavior of the RT tasks.
 
 RT tasks default uclamp_min value can be modified at boot or runtime via
-sysctl. See section 3.4.1.
+sysctl. See below section.
+
+.. _sched-util-clamp-min-rt-default:
 
 3.4.1  sched_util_clamp_min_rt_default:
 ---------------------------------------
 
 Running RT tasks at maximum performance point is expensive on battery powered
-devices and not necessary. To allow system designers to offer good performance
-guarantees for RT tasks without pushing it all the way to maximum performance
+devices and not necessary. To allow system developer to offer good performance
+guarantees for these tasks without pushing it all the way to maximum performance
 point, this sysctl knob allows tuning the best boost value to address the
 system requirement without burning power running at maximum performance point
 all the time.
 
-Application designers are encouraged to use the per task util clamp interface
+Application developer are encouraged to use the per task util clamp interface
 to ensure they are performance and power aware. Ideally this knob should be set
 to 0 by system designers and leave the task of managing performance
-requirements to the apps themselves.
+requirements to the apps.
 
-4.  HOW TO USE UTIL CLAMP:
-==========================
+4. How to use util clamp
+========================
 
 Util clamp promotes the concept of user space assisted power and performance
-management. At the scheduler level the info required to make the best decision
-are non existent. But with util clamp user space can hint to the scheduler to
+management. At the scheduler level there is no info required to make the best
+decision. However, with util clamp user space can hint to the scheduler to
 make better decision about task placement and frequency selection.
 
 Best results are achieved by not making any assumptions about the system the
@@ -530,41 +517,41 @@ dynamically monitor and adjust. Ultimately this will allow for a better user
 experience at a better perf/watt.
 
 For some systems and use cases, static setup will help to achieve good results.
-Portability will be a problem in this case. After all how much work one can do
-at 100, 200 or 1024 is unknown and a special property of every system. Unless
-there's a specific target system, static setup should be avoided.
+Portability will be a problem in this case. How much work one can do at 100,
+200 or 1024 is different for each system. Unless there's a specific target
+system, static setup should be avoided.
 
-All in all there are enough possibilities to create a whole framework based on
+There are enough possibilities to create a whole framework based on
 util clamp or self contained app that makes use of it directly.
 
-4.1  BOOST IMPORTANT AND DVFS-LATENCY-SENSITIVE TASKS:
-------------------------------------------------------
+4.1. Boost important and DVFS-latency-sensitive tasks
+-----------------------------------------------------
 
 A GUI task might not be busy to warrant driving the frequency high when it
-wakes up. But it requires to finish its work within a specific period of time
+wakes up. However, it requires to finish its work within a specific time window
 to deliver the desired user experience. The right frequency it requires at
 wakeup will be system dependent. On some underpowered systems it will be high,
-on other overpowered ones, it will be low or 0.
+on other overpowered ones it will be low or 0.
 
-This task can increase its UCLAMP_MIN value every time it misses a deadline to
-ensure on next wake up it runs at a higher performance point. It should try to
-approach the lowest UCLAMP_MIN value that allows to meet its deadline on any
+This task can increase its UCLAMP_MIN value every time it misses the deadline
+to ensure on next wake up it runs at a higher performance point. It should try
+to approach the lowest UCLAMP_MIN value that allows to meet its deadline on any
 particular system to achieve the best possible perf/watt for that system.
 
 On heterogeneous systems, it might be important for this task to run on
-a bigger CPU.
+a faster CPU.
 
 Generally it is advised to perceive the input as performance level or point
 which will imply both task placement and frequency selection.
 
-4.2  CAP BACKGROUND TASKS:
---------------------------
+4.2. Cap background tasks
+-------------------------
 
 Like explained for Android case in the introduction. Any app can lower
 UCLAMP_MAX for some background tasks that don't care about performance but
 could end up being busy and consume unnecessary system resources on the system.
 
-4.3  POWERSAVE MODE:
+4.3.  Powersave mode
 --------------------
 
 sched_util_clamp_max system wide interface can be used to limit all tasks from
@@ -575,8 +562,8 @@ This is not unique to uclamp as one can achieve the same by reducing max
 frequency of the cpufreq governor. It can be considered a more convenient
 alternative interface.
 
-4.4  PER APP PERFORMANCE RESTRICTIONS:
---------------------------------------
+4.4.  Per-app performance restriction
+-------------------------------------
 
 Middleware/Utility can provide the user an option to set UCLAMP_MIN/MAX for an
 app every time it is executed to guarantee a minimum performance point and/or
@@ -585,28 +572,31 @@ these apps.
 
 If you want to prevent your laptop from heating up while on the go from
 compiling the kernel and happy to sacrifice performance to save power, but
-still would like to keep your browser performance intact; uclamp enables that.
+still would like to keep your browser performance intact, uclamp makes it
+possible.
 
-5.  LIMITATIONS:
-================
+5. Limitations
+==============
 
-5.1  CAPPING FREQUENCY WITH UCLAMP_MAX FAILS UNDER CERTAIN CONDITIONS:
-----------------------------------------------------------------------
+.. _uclamp-capping-fail:
 
-If task p0 is capped to run at 512
+5.1. Capping frequency with uclamp_max fails under certain conditions
+---------------------------------------------------------------------
+
+If task p0 is capped to run at 512:
 
 .. code-block:: c
 
         p0->uclamp[UCLAMP_MAX] = 512
 
-is sharing the rq with p1 which is free to run at any performance point
+and it shares the rq with p1 which is free to run at any performance point:
 
 .. code-block:: c
 
         p1->uclamp[UCLAMP_MAX] = 1024
 
 then due to max aggregation the rq will be allowed to reach max performance
-point
+point:
 
 .. code-block:: c
 
@@ -620,19 +610,19 @@ both are running at the same rq, p1 will cause the frequency capping to be left
 from the rq although p1, which is allowed to run at any performance point,
 doesn't actually need to run at that frequency.
 
-5.2  UCLAMP_MAX CAN BREAK PELT (UTIL_AVG) SIGNAL
+5.2. UCLAMP_MAX can break pelt (util_avg) signal
 ------------------------------------------------
 
 PELT assumes that frequency will always increase as the signals grow to ensure
-there's always some idle time on the CPU. But with UCLAMP_MAX, we will prevent
-this frequency increase which can lead to no idle time in some circumstances.
-When there's no idle time, then a task will look like a busy loop, which would
-result in util_avg being 1024.
+there's always some idle time on the CPU. But with UCLAMP_MAX, this frequency
+increase will be prevented which can lead to no idle time in some
+circumstances. When there's no idle time, a task will stuck in a busy loop,
+which would result in util_avg being 1024.
 
-Combing with issue described in 5.2, this an lead to unwanted frequency spikes
+Combing with issue described below, this an lead to unwanted frequency spikes
 when severely capped tasks share the rq with a small non capped task.
 
-As an example if task p
+As an example if task p, which have:
 
 .. code-block:: c
 
@@ -646,35 +636,35 @@ of.
 
         rq->uclamp[UCLAMP_MAX] = 0
 
-If the ratio of Fmax/Fmin is 3, then
+If the ratio of Fmax/Fmin is 3, then maximum value will be:
 
 .. code-block:: c
 
         300 * (Fmax/Fmin) = 900
 
-Which indicates the CPU will still see idle time since 900 is < 1024. The
-_actual_ util_avg will NOT be 900 though. It will be higher than 300, but won't
-approach 900. As long as there's idle time, p->util_avg updates will be off by
-a some margin, but not proportional to Fmax/Fmin.
+which indicates the CPU will still see idle time since 900 is < 1024. The
+_actual_ util_avg will not be 900 though, but somewhere between 300 and 900. As
+long as there's idle time, p->util_avg updates will be off by a some margin,
+but not proportional to Fmax/Fmin.
 
 .. code-block:: c
 
         p0->util_avg = 300 + small_error
 
-Now if the ratio of Fmax/Fmin is 4, then
+Now if the ratio of Fmax/Fmin is 4, the maximum value becomes:
 
 .. code-block:: c
 
         300 * (Fmax/Fmin) = 1200
 
 which is higher than 1024 and indicates that the CPU has no idle time. When
-this happens, then the _actual_ util_avg will become 1024.
+this happens, then the _actual_ util_avg will become:
 
 .. code-block:: c
 
         p0->util_avg = 1024
 
-If task p1 wakes up on this CPU
+If task p1 wakes up on this CPU, which have:
 
 .. code-block:: c
 
@@ -683,7 +673,7 @@ If task p1 wakes up on this CPU
 
 then the effective UCLAMP_MAX for the CPU will be 1024 according to max
 aggregation rule. But since the capped p0 task was running and throttled
-severely, then the rq->util_avg will be 1024.
+severely, then the rq->util_avg will be:
 
 .. code-block:: c
 
@@ -693,7 +683,7 @@ severely, then the rq->util_avg will be 1024.
         rq->util_avg = 1024
         rq->uclamp[UCLAMP_MAX] = 1024
 
-Hence lead to a frequency spike since if p0 wasn't throttled we should get
+Hence lead to a frequency spike since if p0 wasn't throttled we should get:
 
 .. code-block:: c
 

Thanks.

[1]: https://lore.kernel.org/lkml/20221113152629.3wbyeejsj5v33rvu@airbuntu/

-- 
An old man doll... just what I always wanted! - Clara

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