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Merge back earlier cpuidle material for v5.1.

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Rafael J. Wysocki 2019-02-01 11:57:46 +01:00
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104
Documentation/admin-guide/pm/cpuidle.rst
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@ -155,14 +155,14 @@ governor uses that information depends on what algorithm is implemented by it
and that is the primary reason for having more than one governor in the
``CPUIdle`` subsystem.
There are two ``CPUIdle`` governors available, ``menu`` and ``ladder``. Which
of them is used depends on the configuration of the kernel and in particular on
whether or not the scheduler tick can be `stopped by the idle
loop <idle-cpus-and-tick_>`_. It is possible to change the governor at run time
if the ``cpuidle_sysfs_switch`` command line parameter has been passed to the
kernel, but that is not safe in general, so it should not be done on production
systems (that may change in the future, though). The name of the ``CPUIdle``
governor currently used by the kernel can be read from the
There are three ``CPUIdle`` governors available, ``menu``, `TEO <teo-gov_>`_
and ``ladder``. Which of them is used by default depends on the configuration
of the kernel and in particular on whether or not the scheduler tick can be
`stopped by the idle loop <idle-cpus-and-tick_>`_. It is possible to change the
governor at run time if the ``cpuidle_sysfs_switch`` command line parameter has
been passed to the kernel, but that is not safe in general, so it should not be
done on production systems (that may change in the future, though). The name of
the ``CPUIdle`` governor currently used by the kernel can be read from the
:file:`current_governor_ro` (or :file:`current_governor` if
``cpuidle_sysfs_switch`` is present in the kernel command line) file under
:file:`/sys/devices/system/cpu/cpuidle/` in ``sysfs``.
@ -256,6 +256,8 @@ the ``menu`` governor by default and if it is not tickless, the default
``CPUIdle`` governor on it will be ``ladder``.
.. _menu-gov:
The ``menu`` Governor
=====================
@ -333,6 +335,92 @@ that time, the governor may need to select a shallower state with a suitable
target residency.
.. _teo-gov:
The Timer Events Oriented (TEO) Governor
========================================
The timer events oriented (TEO) governor is an alternative ``CPUIdle`` governor
for tickless systems. It follows the same basic strategy as the ``menu`` `one
<menu-gov_>`_: it always tries to find the deepest idle state suitable for the
given conditions. However, it applies a different approach to that problem.
First, it does not use sleep length correction factors, but instead it attempts
to correlate the observed idle duration values with the available idle states
and use that information to pick up the idle state that is most likely to
"match" the upcoming CPU idle interval. Second, it does not take the tasks
that were running on the given CPU in the past and are waiting on some I/O
operations to complete now at all (there is no guarantee that they will run on
the same CPU when they become runnable again) and the pattern detection code in
it avoids taking timer wakeups into account. It also only uses idle duration
values less than the current time till the closest timer (with the scheduler
tick excluded) for that purpose.
Like in the ``menu`` governor `case <menu-gov_>`_, the first step is to obtain
the *sleep length*, which is the time until the closest timer event with the
assumption that the scheduler tick will be stopped (that also is the upper bound
on the time until the next CPU wakeup). That value is then used to preselect an
idle state on the basis of three metrics maintained for each idle state provided
by the ``CPUIdle`` driver: ``hits``, ``misses`` and ``early_hits``.
The ``hits`` and ``misses`` metrics measure the likelihood that a given idle
state will "match" the observed (post-wakeup) idle duration if it "matches" the
sleep length. They both are subject to decay (after a CPU wakeup) every time
the target residency of the idle state corresponding to them is less than or
equal to the sleep length and the target residency of the next idle state is
greater than the sleep length (that is, when the idle state corresponding to
them "matches" the sleep length). The ``hits`` metric is increased if the
former condition is satisfied and the target residency of the given idle state
is less than or equal to the observed idle duration and the target residency of
the next idle state is greater than the observed idle duration at the same time
(that is, it is increased when the given idle state "matches" both the sleep
length and the observed idle duration). In turn, the ``misses`` metric is
increased when the given idle state "matches" the sleep length only and the
observed idle duration is too short for its target residency.
The ``early_hits`` metric measures the likelihood that a given idle state will
"match" the observed (post-wakeup) idle duration if it does not "match" the
sleep length. It is subject to decay on every CPU wakeup and it is increased
when the idle state corresponding to it "matches" the observed (post-wakeup)
idle duration and the target residency of the next idle state is less than or
equal to the sleep length (i.e. the idle state "matching" the sleep length is
deeper than the given one).
The governor walks the list of idle states provided by the ``CPUIdle`` driver
and finds the last (deepest) one with the target residency less than or equal
to the sleep length. Then, the ``hits`` and ``misses`` metrics of that idle
state are compared with each other and it is preselected if the ``hits`` one is
greater (which means that that idle state is likely to "match" the observed idle
duration after CPU wakeup). If the ``misses`` one is greater, the governor
preselects the shallower idle state with the maximum ``early_hits`` metric
(or if there are multiple shallower idle states with equal ``early_hits``
metric which also is the maximum, the shallowest of them will be preselected).
[If there is a wakeup latency constraint coming from the `PM QoS framework
<cpu-pm-qos_>`_ which is hit before reaching the deepest idle state with the
target residency within the sleep length, the deepest idle state with the exit
latency within the constraint is preselected without consulting the ``hits``,
``misses`` and ``early_hits`` metrics.]
Next, the governor takes several idle duration values observed most recently
into consideration and if at least a half of them are greater than or equal to
the target residency of the preselected idle state, that idle state becomes the
final candidate to ask for. Otherwise, the average of the most recent idle
duration values below the target residency of the preselected idle state is
computed and the governor walks the idle states shallower than the preselected
one and finds the deepest of them with the target residency within that average.
That idle state is then taken as the final candidate to ask for.
Still, at this point the governor may need to refine the idle state selection if
it has not decided to `stop the scheduler tick <idle-cpus-and-tick_>`_. That
generally happens if the target residency of the idle state selected so far is
less than the tick period and the tick has not been stopped already (in a
previous iteration of the idle loop). Then, like in the ``menu`` governor
`case <menu-gov_>`_, the sleep length used in the previous computations may not
reflect the real time until the closest timer event and if it really is greater
than that time, a shallower state with a suitable target residency may need to
be selected.
.. _idle-states-representation:
Representation of Idle States

37
Documentation/cpuidle/driver.txt
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@ -1,37 +0,0 @@
Supporting multiple CPU idle levels in kernel
cpuidle drivers
cpuidle driver hooks into the cpuidle infrastructure and handles the
architecture/platform dependent part of CPU idle states. Driver
provides the platform idle state detection capability and also
has mechanisms in place to support actual entry-exit into CPU idle states.
cpuidle driver initializes the cpuidle_device structure for each CPU device
and registers with cpuidle using cpuidle_register_device.
If all the idle states are the same, the wrapper function cpuidle_register
could be used instead.
It can also support the dynamic changes (like battery <-> AC), by using
cpuidle_pause_and_lock, cpuidle_disable_device and cpuidle_enable_device,
cpuidle_resume_and_unlock.
Interfaces:
extern int cpuidle_register(struct cpuidle_driver *drv,
const struct cpumask *const coupled_cpus);
extern int cpuidle_unregister(struct cpuidle_driver *drv);
extern int cpuidle_register_driver(struct cpuidle_driver *drv);
extern void cpuidle_unregister_driver(struct cpuidle_driver *drv);
extern int cpuidle_register_device(struct cpuidle_device *dev);
extern void cpuidle_unregister_device(struct cpuidle_device *dev);
extern void cpuidle_pause_and_lock(void);
extern void cpuidle_resume_and_unlock(void);
extern int cpuidle_enable_device(struct cpuidle_device *dev);
extern void cpuidle_disable_device(struct cpuidle_device *dev);

28
Documentation/cpuidle/governor.txt
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@ -1,28 +0,0 @@
Supporting multiple CPU idle levels in kernel
cpuidle governors
cpuidle governor is policy routine that decides what idle state to enter at
any given time. cpuidle core uses different callbacks to the governor.
* enable() to enable governor for a particular device
* disable() to disable governor for a particular device
* select() to select an idle state to enter
* reflect() called after returning from the idle state, which can be used
by the governor for some record keeping.
More than one governor can be registered at the same time and
users can switch between drivers using /sysfs interface (when enabled).
More than one governor part is supported for developers to easily experiment
with different governors. By default, most optimal governor based on your
kernel configuration and platform will be selected by cpuidle.
Interfaces:
extern int cpuidle_register_governor(struct cpuidle_governor *gov);
struct cpuidle_governor

282
Documentation/driver-api/pm/cpuidle.rst Normal file
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@ -0,0 +1,282 @@
.. |struct cpuidle_governor| replace:: :c:type:`struct cpuidle_governor <cpuidle_governor>`
.. |struct cpuidle_device| replace:: :c:type:`struct cpuidle_device <cpuidle_device>`
.. |struct cpuidle_driver| replace:: :c:type:`struct cpuidle_driver <cpuidle_driver>`
.. |struct cpuidle_state| replace:: :c:type:`struct cpuidle_state <cpuidle_state>`
========================
CPU Idle Time Management
========================
::
Copyright (c) 2019 Intel Corp., Rafael J. Wysocki <rafael.j.wysocki@intel.com>
CPU Idle Time Management Subsystem
==================================
Every time one of the logical CPUs in the system (the entities that appear to
fetch and execute instructions: hardware threads, if present, or processor
cores) is idle after an interrupt or equivalent wakeup event, which means that
there are no tasks to run on it except for the special "idle" task associated
with it, there is an opportunity to save energy for the processor that it
belongs to. That can be done by making the idle logical CPU stop fetching
instructions from memory and putting some of the processor's functional units
depended on by it into an idle state in which they will draw less power.
However, there may be multiple different idle states that can be used in such a
situation in principle, so it may be necessary to find the most suitable one
(from the kernel perspective) and ask the processor to use (or "enter") that
particular idle state. That is the role of the CPU idle time management
subsystem in the kernel, called ``CPUIdle``.
The design of ``CPUIdle`` is modular and based on the code duplication avoidance
principle, so the generic code that in principle need not depend on the hardware
or platform design details in it is separate from the code that interacts with
the hardware. It generally is divided into three categories of functional
units: *governors* responsible for selecting idle states to ask the processor
to enter, *drivers* that pass the governors' decisions on to the hardware and
the *core* providing a common framework for them.
CPU Idle Time Governors
=======================
A CPU idle time (``CPUIdle``) governor is a bundle of policy code invoked when
one of the logical CPUs in the system turns out to be idle. Its role is to
select an idle state to ask the processor to enter in order to save some energy.
``CPUIdle`` governors are generic and each of them can be used on any hardware
platform that the Linux kernel can run on. For this reason, data structures
operated on by them cannot depend on any hardware architecture or platform
design details as well.
The governor itself is represented by a |struct cpuidle_governor| object
containing four callback pointers, :c:member:`enable`, :c:member:`disable`,
:c:member:`select`, :c:member:`reflect`, a :c:member:`rating` field described
below, and a name (string) used for identifying it.
For the governor to be available at all, that object needs to be registered
with the ``CPUIdle`` core by calling :c:func:`cpuidle_register_governor()` with
a pointer to it passed as the argument. If successful, that causes the core to
add the governor to the global list of available governors and, if it is the
only one in the list (that is, the list was empty before) or the value of its
:c:member:`rating` field is greater than the value of that field for the
governor currently in use, or the name of the new governor was passed to the
kernel as the value of the ``cpuidle.governor=`` command line parameter, the new
governor will be used from that point on (there can be only one ``CPUIdle``
governor in use at a time). Also, if ``cpuidle_sysfs_switch`` is passed to the
kernel in the command line, user space can choose the ``CPUIdle`` governor to
use at run time via ``sysfs``.
Once registered, ``CPUIdle`` governors cannot be unregistered, so it is not
practical to put them into loadable kernel modules.
The interface between ``CPUIdle`` governors and the core consists of four
callbacks:
:c:member:`enable`
::
int (*enable) (struct cpuidle_driver *drv, struct cpuidle_device *dev);
The role of this callback is to prepare the governor for handling the
(logical) CPU represented by the |struct cpuidle_device| object pointed
to by the ``dev`` argument. The |struct cpuidle_driver| object pointed
to by the ``drv`` argument represents the ``CPUIdle`` driver to be used
with that CPU (among other things, it should contain the list of
|struct cpuidle_state| objects representing idle states that the
processor holding the given CPU can be asked to enter).
It may fail, in which case it is expected to return a negative error
code, and that causes the kernel to run the architecture-specific
default code for idle CPUs on the CPU in question instead of ``CPUIdle``
until the ``->enable()`` governor callback is invoked for that CPU
again.
:c:member:`disable`
::
void (*disable) (struct cpuidle_driver *drv, struct cpuidle_device *dev);
Called to make the governor stop handling the (logical) CPU represented
by the |struct cpuidle_device| object pointed to by the ``dev``
argument.
It is expected to reverse any changes made by the ``->enable()``
callback when it was last invoked for the target CPU, free all memory
allocated by that callback and so on.
:c:member:`select`
::
int (*select) (struct cpuidle_driver *drv, struct cpuidle_device *dev,
bool *stop_tick);
Called to select an idle state for the processor holding the (logical)
CPU represented by the |struct cpuidle_device| object pointed to by the
``dev`` argument.
The list of idle states to take into consideration is represented by the
:c:member:`states` array of |struct cpuidle_state| objects held by the
|struct cpuidle_driver| object pointed to by the ``drv`` argument (which
represents the ``CPUIdle`` driver to be used with the CPU at hand). The
value returned by this callback is interpreted as an index into that
array (unless it is a negative error code).
The ``stop_tick`` argument is used to indicate whether or not to stop
the scheduler tick before asking the processor to enter the selected
idle state. When the ``bool`` variable pointed to by it (which is set
to ``true`` before invoking this callback) is cleared to ``false``, the
processor will be asked to enter the selected idle state without
stopping the scheduler tick on the given CPU (if the tick has been
stopped on that CPU already, however, it will not be restarted before
asking the processor to enter the idle state).
This callback is mandatory (i.e. the :c:member:`select` callback pointer
in |struct cpuidle_governor| must not be ``NULL`` for the registration
of the governor to succeed).
:c:member:`reflect`
::
void (*reflect) (struct cpuidle_device *dev, int index);
Called to allow the governor to evaluate the accuracy of the idle state
selection made by the ``->select()`` callback (when it was invoked last
time) and possibly use the result of that to improve the accuracy of
idle state selections in the future.
In addition, ``CPUIdle`` governors are required to take power management
quality of service (PM QoS) constraints on the processor wakeup latency into
account when selecting idle states. In order to obtain the current effective
PM QoS wakeup latency constraint for a given CPU, a ``CPUIdle`` governor is
expected to pass the number of the CPU to
:c:func:`cpuidle_governor_latency_req()`. Then, the governor's ``->select()``
callback must not return the index of an indle state whose
:c:member:`exit_latency` value is greater than the number returned by that
function.
CPU Idle Time Management Drivers
================================
CPU idle time management (``CPUIdle``) drivers provide an interface between the
other parts of ``CPUIdle`` and the hardware.
First of all, a ``CPUIdle`` driver has to populate the :c:member:`states` array
of |struct cpuidle_state| objects included in the |struct cpuidle_driver| object
representing it. Going forward this array will represent the list of available
idle states that the processor hardware can be asked to enter shared by all of
the logical CPUs handled by the given driver.
The entries in the :c:member:`states` array are expected to be sorted by the
value of the :c:member:`target_residency` field in |struct cpuidle_state| in
the ascending order (that is, index 0 should correspond to the idle state with
the minimum value of :c:member:`target_residency`). [Since the
:c:member:`target_residency` value is expected to reflect the "depth" of the
idle state represented by the |struct cpuidle_state| object holding it, this
sorting order should be the same as the ascending sorting order by the idle
state "depth".]
Three fields in |struct cpuidle_state| are used by the existing ``CPUIdle``
governors for computations related to idle state selection:
:c:member:`target_residency`
Minimum time to spend in this idle state including the time needed to
enter it (which may be substantial) to save more energy than could
be saved by staying in a shallower idle state for the same amount of
time, in microseconds.
:c:member:`exit_latency`
Maximum time it will take a CPU asking the processor to enter this idle
state to start executing the first instruction after a wakeup from it,
in microseconds.
:c:member:`flags`
Flags representing idle state properties. Currently, governors only use
the ``CPUIDLE_FLAG_POLLING`` flag which is set if the given object
does not represent a real idle state, but an interface to a software
"loop" that can be used in order to avoid asking the processor to enter
any idle state at all. [There are other flags used by the ``CPUIdle``
core in special situations.]
The :c:member:`enter` callback pointer in |struct cpuidle_state|, which must not
be ``NULL``, points to the routine to execute in order to ask the processor to
enter this particular idle state:
::
void (*enter) (struct cpuidle_device *dev, struct cpuidle_driver *drv,
int index);
The first two arguments of it point to the |struct cpuidle_device| object
representing the logical CPU running this callback and the
|struct cpuidle_driver| object representing the driver itself, respectively,
and the last one is an index of the |struct cpuidle_state| entry in the driver's
:c:member:`states` array representing the idle state to ask the processor to
enter.
The analogous ``->enter_s2idle()`` callback in |struct cpuidle_state| is used
only for implementing the suspend-to-idle system-wide power management feature.
The difference between in and ``->enter()`` is that it must not re-enable
interrupts at any point (even temporarily) or attempt to change the states of
clock event devices, which the ``->enter()`` callback may do sometimes.
Once the :c:member:`states` array has been populated, the number of valid
entries in it has to be stored in the :c:member:`state_count` field of the
|struct cpuidle_driver| object representing the driver. Moreover, if any
entries in the :c:member:`states` array represent "coupled" idle states (that
is, idle states that can only be asked for if multiple related logical CPUs are
idle), the :c:member:`safe_state_index` field in |struct cpuidle_driver| needs
to be the index of an idle state that is not "coupled" (that is, one that can be
asked for if only one logical CPU is idle).
In addition to that, if the given ``CPUIdle`` driver is only going to handle a
subset of logical CPUs in the system, the :c:member:`cpumask` field in its
|struct cpuidle_driver| object must point to the set (mask) of CPUs that will be
handled by it.
A ``CPUIdle`` driver can only be used after it has been registered. If there
are no "coupled" idle state entries in the driver's :c:member:`states` array,
that can be accomplished by passing the driver's |struct cpuidle_driver| object
to :c:func:`cpuidle_register_driver()`. Otherwise, :c:func:`cpuidle_register()`
should be used for this purpose.
However, it also is necessary to register |struct cpuidle_device| objects for
all of the logical CPUs to be handled by the given ``CPUIdle`` driver with the
help of :c:func:`cpuidle_register_device()` after the driver has been registered
and :c:func:`cpuidle_register_driver()`, unlike :c:func:`cpuidle_register()`,
does not do that automatically. For this reason, the drivers that use
:c:func:`cpuidle_register_driver()` to register themselves must also take care
of registering the |struct cpuidle_device| objects as needed, so it is generally
recommended to use :c:func:`cpuidle_register()` for ``CPUIdle`` driver
registration in all cases.
The registration of a |struct cpuidle_device| object causes the ``CPUIdle``
``sysfs`` interface to be created and the governor's ``->enable()`` callback to
be invoked for the logical CPU represented by it, so it must take place after
registering the driver that will handle the CPU in question.
``CPUIdle`` drivers and |struct cpuidle_device| objects can be unregistered
when they are not necessary any more which allows some resources associated with
them to be released. Due to dependencies between them, all of the
|struct cpuidle_device| objects representing CPUs handled by the given
``CPUIdle`` driver must be unregistered, with the help of
:c:func:`cpuidle_unregister_device()`, before calling
:c:func:`cpuidle_unregister_driver()` to unregister the driver. Alternatively,
:c:func:`cpuidle_unregister()` can be called to unregister a ``CPUIdle`` driver
along with all of the |struct cpuidle_device| objects representing CPUs handled
by it.
``CPUIdle`` drivers can respond to runtime system configuration changes that
lead to modifications of the list of available processor idle states (which can
happen, for example, when the system's power source is switched from AC to
battery or the other way around). Upon a notification of such a change,
a ``CPUIdle`` driver is expected to call :c:func:`cpuidle_pause_and_lock()` to
turn ``CPUIdle`` off temporarily and then :c:func:`cpuidle_disable_device()` for
all of the |struct cpuidle_device| objects representing CPUs affected by that
change. Next, it can update its :c:member:`states` array in accordance with
the new configuration of the system, call :c:func:`cpuidle_enable_device()` for
all of the relevant |struct cpuidle_device| objects and invoke
:c:func:`cpuidle_resume_and_unlock()` to allow ``CPUIdle`` to be used again.

7
Documentation/driver-api/pm/index.rst
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@ -1,9 +1,10 @@
=======================
Device Power Management
=======================
===============================
CPU and Device Power Management
===============================
.. toctree::
cpuidle
devices
notifiers
types

1
MAINTAINERS
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@ -4016,6 +4016,7 @@ S: Maintained
T: git git://git.kernel.org/pub/scm/linux/kernel/git/rafael/linux-pm.git
B: https://bugzilla.kernel.org
F: Documentation/admin-guide/pm/cpuidle.rst
F: Documentation/driver-api/pm/cpuidle.rst
F: drivers/cpuidle/*
F: include/linux/cpuidle.h

11
drivers/cpuidle/Kconfig
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@ -4,7 +4,7 @@ config CPU_IDLE
bool "CPU idle PM support"
default y if ACPI || PPC_PSERIES
select CPU_IDLE_GOV_LADDER if (!NO_HZ && !NO_HZ_IDLE)
select CPU_IDLE_GOV_MENU if (NO_HZ || NO_HZ_IDLE)
select CPU_IDLE_GOV_MENU if (NO_HZ || NO_HZ_IDLE) && !CPU_IDLE_GOV_TEO
help
CPU idle is a generic framework for supporting software-controlled
idle processor power management. It includes modular cross-platform
@ -23,6 +23,15 @@ config CPU_IDLE_GOV_LADDER
config CPU_IDLE_GOV_MENU
bool "Menu governor (for tickless system)"
config CPU_IDLE_GOV_TEO
bool "Timer events oriented (TEO) governor (for tickless systems)"
help
This governor implements a simplified idle state selection method
focused on timer events and does not do any interactivity boosting.
Some workloads benefit from using it and it generally should be safe
to use. Say Y here if you are not happy with the alternatives.
config DT_IDLE_STATES
bool

1
drivers/cpuidle/governors/Makefile
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@ -4,3 +4,4 @@
obj-$(CONFIG_CPU_IDLE_GOV_LADDER) += ladder.o
obj-$(CONFIG_CPU_IDLE_GOV_MENU) += menu.o
obj-$(CONFIG_CPU_IDLE_GOV_TEO) += teo.o

444
drivers/cpuidle/governors/teo.c Normal file
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@ -0,0 +1,444 @@
// SPDX-License-Identifier: GPL-2.0
/*
* Timer events oriented CPU idle governor
*
* Copyright (C) 2018 Intel Corporation
* Author: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
*
* The idea of this governor is based on the observation that on many systems
* timer events are two or more orders of magnitude more frequent than any
* other interrupts, so they are likely to be the most significant source of CPU
* wakeups from idle states. Moreover, information about what happened in the
* (relatively recent) past can be used to estimate whether or not the deepest
* idle state with target residency within the time to the closest timer is
* likely to be suitable for the upcoming idle time of the CPU and, if not, then
* which of the shallower idle states to choose.
*
* Of course, non-timer wakeup sources are more important in some use cases and
* they can be covered by taking a few most recent idle time intervals of the
* CPU into account. However, even in that case it is not necessary to consider
* idle duration values greater than the time till the closest timer, as the
* patterns that they may belong to produce average values close enough to
* the time till the closest timer (sleep length) anyway.
*
* Thus this governor estimates whether or not the upcoming idle time of the CPU
* is likely to be significantly shorter than the sleep length and selects an
* idle state for it in accordance with that, as follows:
*
* - Find an idle state on the basis of the sleep length and state statistics
* collected over time:
*
* o Find the deepest idle state whose target residency is less than or equal
* to the sleep length.
*
* o Select it if it matched both the sleep length and the observed idle
* duration in the past more often than it matched the sleep length alone
* (i.e. the observed idle duration was significantly shorter than the sleep
* length matched by it).
*
* o Otherwise, select the shallower state with the greatest matched "early"
* wakeups metric.
*
* - If the majority of the most recent idle duration values are below the
* target residency of the idle state selected so far, use those values to
* compute the new expected idle duration and find an idle state matching it
* (which has to be shallower than the one selected so far).
*/
#include <linux/cpuidle.h>
#include <linux/jiffies.h>
#include <linux/kernel.h>
#include <linux/sched/clock.h>
#include <linux/tick.h>
/*
* The PULSE value is added to metrics when they grow and the DECAY_SHIFT value
* is used for decreasing metrics on a regular basis.
*/
#define PULSE 1024
#define DECAY_SHIFT 3
/*
* Number of the most recent idle duration values to take into consideration for
* the detection of wakeup patterns.
*/
#define INTERVALS 8
/**
* struct teo_idle_state - Idle state data used by the TEO cpuidle governor.
* @early_hits: "Early" CPU wakeups "matching" this state.
* @hits: "On time" CPU wakeups "matching" this state.
* @misses: CPU wakeups "missing" this state.
*
* A CPU wakeup is "matched" by a given idle state if the idle duration measured
* after the wakeup is between the target residency of that state and the target
* residency of the next one (or if this is the deepest available idle state, it
* "matches" a CPU wakeup when the measured idle duration is at least equal to
* its target residency).
*
* Also, from the TEO governor perspective, a CPU wakeup from idle is "early" if
* it occurs significantly earlier than the closest expected timer event (that
* is, early enough to match an idle state shallower than the one matching the
* time till the closest timer event). Otherwise, the wakeup is "on time", or
* it is a "hit".
*
* A "miss" occurs when the given state doesn't match the wakeup, but it matches
* the time till the closest timer event used for idle state selection.
*/
struct teo_idle_state {
unsigned int early_hits;
unsigned int hits;
unsigned int misses;
};
/**
* struct teo_cpu - CPU data used by the TEO cpuidle governor.
* @time_span_ns: Time between idle state selection and post-wakeup update.
* @sleep_length_ns: Time till the closest timer event (at the selection time).
* @states: Idle states data corresponding to this CPU.
* @last_state: Idle state entered by the CPU last time.
* @interval_idx: Index of the most recent saved idle interval.
* @intervals: Saved idle duration values.
*/
struct teo_cpu {
u64 time_span_ns;
u64 sleep_length_ns;
struct teo_idle_state states[CPUIDLE_STATE_MAX];
int last_state;
int interval_idx;
unsigned int intervals[INTERVALS];
};
static DEFINE_PER_CPU(struct teo_cpu, teo_cpus);
/**
* teo_update - Update CPU data after wakeup.
* @drv: cpuidle driver containing state data.
* @dev: Target CPU.
*/
static void teo_update(struct cpuidle_driver *drv, struct cpuidle_device *dev)
{
struct teo_cpu *cpu_data = per_cpu_ptr(&teo_cpus, dev->cpu);
unsigned int sleep_length_us = ktime_to_us(cpu_data->sleep_length_ns);
int i, idx_hit = -1, idx_timer = -1;
unsigned int measured_us;
if (cpu_data->time_span_ns >= cpu_data->sleep_length_ns) {
/*
* One of the safety nets has triggered or this was a timer
* wakeup (or equivalent).
*/
measured_us = sleep_length_us;
} else {
unsigned int lat = drv->states[cpu_data->last_state].exit_latency;
measured_us = ktime_to_us(cpu_data->time_span_ns);
/*
* The delay between the wakeup and the first instruction
* executed by the CPU is not likely to be worst-case every
* time, so take 1/2 of the exit latency as a very rough
* approximation of the average of it.
*/
if (measured_us >= lat)
measured_us -= lat / 2;
else
measured_us /= 2;
}
/*
* Decay the "early hits" metric for all of the states and find the
* states matching the sleep length and the measured idle duration.
*/
for (i = 0; i < drv->state_count; i++) {
unsigned int early_hits = cpu_data->states[i].early_hits;
cpu_data->states[i].early_hits -= early_hits >> DECAY_SHIFT;
if (drv->states[i].target_residency <= sleep_length_us) {
idx_timer = i;
if (drv->states[i].target_residency <= measured_us)
idx_hit = i;
}
}
/*
* Update the "hits" and "misses" data for the state matching the sleep
* length. If it matches the measured idle duration too, this is a hit,
* so increase the "hits" metric for it then. Otherwise, this is a
* miss, so increase the "misses" metric for it. In the latter case
* also increase the "early hits" metric for the state that actually
* matches the measured idle duration.
*/
if (idx_timer >= 0) {
unsigned int hits = cpu_data->states[idx_timer].hits;
unsigned int misses = cpu_data->states[idx_timer].misses;
hits -= hits >> DECAY_SHIFT;
misses -= misses >> DECAY_SHIFT;
if (idx_timer > idx_hit) {
misses += PULSE;
if (idx_hit >= 0)
cpu_data->states[idx_hit].early_hits += PULSE;
} else {
hits += PULSE;
}
cpu_data->states[idx_timer].misses = misses;
cpu_data->states[idx_timer].hits = hits;
}
/*
* If the total time span between idle state selection and the "reflect"
* callback is greater than or equal to the sleep length determined at
* the idle state selection time, the wakeup is likely to be due to a
* timer event.
*/
if (cpu_data->time_span_ns >= cpu_data->sleep_length_ns)
measured_us = UINT_MAX;
/*
* Save idle duration values corresponding to non-timer wakeups for
* pattern detection.
*/
cpu_data->intervals[cpu_data->interval_idx++] = measured_us;
if (cpu_data->interval_idx > INTERVALS)
cpu_data->interval_idx = 0;
}
/**
* teo_find_shallower_state - Find shallower idle state matching given duration.
* @drv: cpuidle driver containing state data.
* @dev: Target CPU.
* @state_idx: Index of the capping idle state.
* @duration_us: Idle duration value to match.
*/
static int teo_find_shallower_state(struct cpuidle_driver *drv,
struct cpuidle_device *dev, int state_idx,
unsigned int duration_us)
{
int i;
for (i = state_idx - 1; i >= 0; i--) {
if (drv->states[i].disabled || dev->states_usage[i].disable)
continue;
state_idx = i;
if (drv->states[i].target_residency <= duration_us)
break;
}
return state_idx;
}
/**
* teo_select - Selects the next idle state to enter.
* @drv: cpuidle driver containing state data.
* @dev: Target CPU.
* @stop_tick: Indication on whether or not to stop the scheduler tick.
*/
static int teo_select(struct cpuidle_driver *drv, struct cpuidle_device *dev,
bool *stop_tick)
{
struct teo_cpu *cpu_data = per_cpu_ptr(&teo_cpus, dev->cpu);
int latency_req = cpuidle_governor_latency_req(dev->cpu);
unsigned int duration_us, count;
int max_early_idx, idx, i;
ktime_t delta_tick;
if (cpu_data->last_state >= 0) {
teo_update(drv, dev);
cpu_data->last_state = -1;
}
cpu_data->time_span_ns = local_clock();
cpu_data->sleep_length_ns = tick_nohz_get_sleep_length(&delta_tick);
duration_us = ktime_to_us(cpu_data->sleep_length_ns);
count = 0;
max_early_idx = -1;
idx = -1;
for (i = 0; i < drv->state_count; i++) {
struct cpuidle_state *s = &drv->states[i];
struct cpuidle_state_usage *su = &dev->states_usage[i];
if (s->disabled || su->disable) {
/*
* If the "early hits" metric of a disabled state is
* greater than the current maximum, it should be taken
* into account, because it would be a mistake to select
* a deeper state with lower "early hits" metric. The
* index cannot be changed to point to it, however, so
* just increase the max count alone and let the index
* still point to a shallower idle state.
*/
if (max_early_idx >= 0 &&
count < cpu_data->states[i].early_hits)
count = cpu_data->states[i].early_hits;
continue;
}
if (idx < 0)
idx = i; /* first enabled state */
if (s->target_residency > duration_us)
break;
if (s->exit_latency > latency_req) {
/*
* If we break out of the loop for latency reasons, use
* the target residency of the selected state as the
* expected idle duration to avoid stopping the tick
* as long as that target residency is low enough.
*/
duration_us = drv->states[idx].target_residency;
goto refine;
}
idx = i;
if (count < cpu_data->states[i].early_hits &&
!(tick_nohz_tick_stopped() &&
drv->states[i].target_residency < TICK_USEC)) {
count = cpu_data->states[i].early_hits;
max_early_idx = i;
}
}
/*
* If the "hits" metric of the idle state matching the sleep length is
* greater than its "misses" metric, that is the one to use. Otherwise,
* it is more likely that one of the shallower states will match the
* idle duration observed after wakeup, so take the one with the maximum
* "early hits" metric, but if that cannot be determined, just use the
* state selected so far.
*/
if (cpu_data->states[idx].hits <= cpu_data->states[idx].misses &&
max_early_idx >= 0) {
idx = max_early_idx;
duration_us = drv->states[idx].target_residency;
}
refine:
if (idx < 0) {
idx = 0; /* No states enabled. Must use 0. */
} else if (idx > 0) {
u64 sum = 0;
count = 0;
/*
* Count and sum the most recent idle duration values less than
* the target residency of the state selected so far, find the
* max.
*/
for (i = 0; i < INTERVALS; i++) {
unsigned int val = cpu_data->intervals[i];
if (val >= drv->states[idx].target_residency)
continue;
count++;
sum += val;
}
/*
* Give up unless the majority of the most recent idle duration
* values are in the interesting range.
*/
if (count > INTERVALS / 2) {
unsigned int avg_us = div64_u64(sum, count);
/*
* Avoid spending too much time in an idle state that
* would be too shallow.
*/
if (!(tick_nohz_tick_stopped() && avg_us < TICK_USEC)) {
idx = teo_find_shallower_state(drv, dev, idx, avg_us);
duration_us = avg_us;
}
}
}
/*
* Don't stop the tick if the selected state is a polling one or if the
* expected idle duration is shorter than the tick period length.
*/
if (((drv->states[idx].flags & CPUIDLE_FLAG_POLLING) ||
duration_us < TICK_USEC) && !tick_nohz_tick_stopped()) {
unsigned int delta_tick_us = ktime_to_us(delta_tick);
*stop_tick = false;
/*
* The tick is not going to be stopped, so if the target
* residency of the state to be returned is not within the time
* till the closest timer including the tick, try to correct
* that.
*/
if (idx > 0 && drv->states[idx].target_residency > delta_tick_us)
idx = teo_find_shallower_state(drv, dev, idx, delta_tick_us);
}
return idx;
}
/**
* teo_reflect - Note that governor data for the CPU need to be updated.
* @dev: Target CPU.
* @state: Entered state.
*/
static void teo_reflect(struct cpuidle_device *dev, int state)
{
struct teo_cpu *cpu_data = per_cpu_ptr(&teo_cpus, dev->cpu);
cpu_data->last_state = state;
/*
* If the wakeup was not "natural", but triggered by one of the safety
* nets, assume that the CPU might have been idle for the entire sleep
* length time.
*/
if (dev->poll_time_limit ||
(tick_nohz_idle_got_tick() && cpu_data->sleep_length_ns > TICK_NSEC)) {
dev->poll_time_limit = false;
cpu_data->time_span_ns = cpu_data->sleep_length_ns;
} else {
cpu_data->time_span_ns = local_clock() - cpu_data->time_span_ns;
}
}
/**
* teo_enable_device - Initialize the governor's data for the target CPU.
* @drv: cpuidle driver (not used).
* @dev: Target CPU.
*/
static int teo_enable_device(struct cpuidle_driver *drv,
struct cpuidle_device *dev)
{
struct teo_cpu *cpu_data = per_cpu_ptr(&teo_cpus, dev->cpu);
int i;
memset(cpu_data, 0, sizeof(*cpu_data));
for (i = 0; i < INTERVALS; i++)
cpu_data->intervals[i] = UINT_MAX;
return 0;
}
static struct cpuidle_governor teo_governor = {
.name = "teo",
.rating = 19,
.enable = teo_enable_device,
.select = teo_select,
.reflect = teo_reflect,
};
static int __init teo_governor_init(void)
{
return cpuidle_register_governor(&teo_governor);
}
postcore_initcall(teo_governor_init);

8
include/linux/cpuidle.h
View File

@ -69,11 +69,9 @@ struct cpuidle_state {
/* Idle State Flags */
#define CPUIDLE_FLAG_NONE (0x00)
#define CPUIDLE_FLAG_POLLING (0x01) /* polling state */
#define CPUIDLE_FLAG_COUPLED (0x02) /* state applies to multiple cpus */
#define CPUIDLE_FLAG_TIMER_STOP (0x04) /* timer is stopped on this state */
#define CPUIDLE_DRIVER_FLAGS_MASK (0xFFFF0000)
#define CPUIDLE_FLAG_POLLING BIT(0) /* polling state */
#define CPUIDLE_FLAG_COUPLED BIT(1) /* state applies to multiple cpus */
#define CPUIDLE_FLAG_TIMER_STOP BIT(2) /* timer is stopped on this state */
struct cpuidle_device_kobj;
struct cpuidle_state_kobj;