If the userspace hasn't been prepared to ignore the unreliable "opened"
events and the unreliable initial state notification, Linux users can use
the following kernel parameters to handle the possible issues:
-A. button.lid_init_state=open:
+A. button.lid_init_state=method:
+ When this option is specified, the ACPI button driver reports the
+ initial lid state using the returning value of the _LID control method
+ and whether the "opened"/"closed" events are paired fully relies on the
+ firmware implementation.
+ This option can be used to fix some platforms where the returning value
+ of the _LID control method is reliable but the initial lid state
+ notification is missing.
+ This option is the default behavior during the period the userspace
+ isn't ready to handle the buggy AML tables.
+B. button.lid_init_state=open:
When this option is specified, the ACPI button driver always reports the
initial lid state as "opened" and whether the "opened"/"closed" events
are paired fully relies on the firmware implementation.
This may fix some platforms where the returning value of the _LID
control method is not reliable and the initial lid state notification is
missing.
- This option is the default behavior during the period the userspace
- isn't ready to handle the buggy AML tables.
If the userspace has been prepared to ignore the unreliable "opened" events
and the unreliable initial state notification, Linux users should always
use the following kernel parameter:
-B. button.lid_init_state=ignore:
+C. button.lid_init_state=ignore:
When this option is specified, the ACPI button driver never reports the
initial lid state and there is a compensation mechanism implemented to
ensure that the reliable "closed" notifications can always be delievered
.. |struct cpufreq_policy| replace:: :c:type:`struct cpufreq_policy <cpufreq_policy>`
+.. |intel_pstate| replace:: :doc:`intel_pstate <intel_pstate>`
=======================
CPU Performance Scaling
interface it comes from and may not be easily represented in an abstract,
platform-independent way. For this reason, ``CPUFreq`` allows scaling drivers
to bypass the governor layer and implement their own performance scaling
-algorithms. That is done by the ``intel_pstate`` scaling driver.
+algorithms. That is done by the |intel_pstate| scaling driver.
``CPUFreq`` Policy Objects
into account. That is achieved by invoking the governor's ``->stop`` and
``->start()`` callbacks, in this order, for the entire policy.
-As mentioned before, the ``intel_pstate`` scaling driver bypasses the scaling
+As mentioned before, the |intel_pstate| scaling driver bypasses the scaling
governor layer of ``CPUFreq`` and provides its own P-state selection algorithms.
-Consequently, if ``intel_pstate`` is used, scaling governors are not attached to
+Consequently, if |intel_pstate| is used, scaling governors are not attached to
new policy objects. Instead, the driver's ``->setpolicy()`` callback is invoked
to register per-CPU utilization update callbacks for each policy. These
callbacks are invoked by the CPU scheduler in the same way as for scaling
-governors, but in the ``intel_pstate`` case they both determine the P-state to
+governors, but in the |intel_pstate| case they both determine the P-state to
use and change the hardware configuration accordingly in one go from scheduler
context.
``scaling_available_governors``
List of ``CPUFreq`` scaling governors present in the kernel that can
- be attached to this policy or (if the ``intel_pstate`` scaling driver is
+ be attached to this policy or (if the |intel_pstate| scaling driver is
in use) list of scaling algorithms provided by the driver that can be
applied to this policy.
the CPU is actually running at (due to hardware design and other
limitations).
- Some scaling drivers (e.g. ``intel_pstate``) attempt to provide
+ Some scaling drivers (e.g. |intel_pstate|) attempt to provide
information more precisely reflecting the current CPU frequency through
this attribute, but that still may not be the exact current CPU
frequency as seen by the hardware at the moment.
``scaling_governor``
The scaling governor currently attached to this policy or (if the
- ``intel_pstate`` scaling driver is in use) the scaling algorithm
+ |intel_pstate| scaling driver is in use) the scaling algorithm
provided by the driver that is currently applied to this policy.
This attribute is read-write and writing to it will cause a new scaling
governor to be attached to this policy or a new scaling algorithm
provided by the scaling driver to be applied to it (in the
- ``intel_pstate`` case), as indicated by the string written to this
+ |intel_pstate| case), as indicated by the string written to this
attribute (which must be one of the names listed by the
``scaling_available_governors`` attribute described above).
the "boost" setting for the whole system. It is not present if the underlying
scaling driver does not support the frequency boost mechanism (or supports it,
but provides a driver-specific interface for controlling it, like
-``intel_pstate``).
+|intel_pstate|).
If the value in this file is 1, the frequency boost mechanism is enabled. This
means that either the hardware can be put into states in which it is able to
--- /dev/null
+===============================================
+``intel_pstate`` CPU Performance Scaling Driver
+===============================================
+
+::
+
+ Copyright (c) 2017 Intel Corp., Rafael J. Wysocki <rafael.j.wysocki@intel.com>
+
+
+General Information
+===================
+
+``intel_pstate`` is a part of the
+:doc:`CPU performance scaling subsystem <cpufreq>` in the Linux kernel
+(``CPUFreq``). It is a scaling driver for the Sandy Bridge and later
+generations of Intel processors. Note, however, that some of those processors
+may not be supported. [To understand ``intel_pstate`` it is necessary to know
+how ``CPUFreq`` works in general, so this is the time to read :doc:`cpufreq` if
+you have not done that yet.]
+
+For the processors supported by ``intel_pstate``, the P-state concept is broader
+than just an operating frequency or an operating performance point (see the
+`LinuxCon Europe 2015 presentation by Kristen Accardi <LCEU2015_>`_ for more
+information about that). For this reason, the representation of P-states used
+by ``intel_pstate`` internally follows the hardware specification (for details
+refer to `Intel® 64 and IA-32 Architectures Software Developer’s Manual
+Volume 3: System Programming Guide <SDM_>`_). However, the ``CPUFreq`` core
+uses frequencies for identifying operating performance points of CPUs and
+frequencies are involved in the user space interface exposed by it, so
+``intel_pstate`` maps its internal representation of P-states to frequencies too
+(fortunately, that mapping is unambiguous). At the same time, it would not be
+practical for ``intel_pstate`` to supply the ``CPUFreq`` core with a table of
+available frequencies due to the possible size of it, so the driver does not do
+that. Some functionality of the core is limited by that.
+
+Since the hardware P-state selection interface used by ``intel_pstate`` is
+available at the logical CPU level, the driver always works with individual
+CPUs. Consequently, if ``intel_pstate`` is in use, every ``CPUFreq`` policy
+object corresponds to one logical CPU and ``CPUFreq`` policies are effectively
+equivalent to CPUs. In particular, this means that they become "inactive" every
+time the corresponding CPU is taken offline and need to be re-initialized when
+it goes back online.
+
+``intel_pstate`` is not modular, so it cannot be unloaded, which means that the
+only way to pass early-configuration-time parameters to it is via the kernel
+command line. However, its configuration can be adjusted via ``sysfs`` to a
+great extent. In some configurations it even is possible to unregister it via
+``sysfs`` which allows another ``CPUFreq`` scaling driver to be loaded and
+registered (see `below <status_attr_>`_).
+
+
+Operation Modes
+===============
+
+``intel_pstate`` can operate in three different modes: in the active mode with
+or without hardware-managed P-states support and in the passive mode. Which of
+them will be in effect depends on what kernel command line options are used and
+on the capabilities of the processor.
+
+Active Mode
+-----------
+
+This is the default operation mode of ``intel_pstate``. If it works in this
+mode, the ``scaling_driver`` policy attribute in ``sysfs`` for all ``CPUFreq``
+policies contains the string "intel_pstate".
+
+In this mode the driver bypasses the scaling governors layer of ``CPUFreq`` and
+provides its own scaling algorithms for P-state selection. Those algorithms
+can be applied to ``CPUFreq`` policies in the same way as generic scaling
+governors (that is, through the ``scaling_governor`` policy attribute in
+``sysfs``). [Note that different P-state selection algorithms may be chosen for
+different policies, but that is not recommended.]
+
+They are not generic scaling governors, but their names are the same as the
+names of some of those governors. Moreover, confusingly enough, they generally
+do not work in the same way as the generic governors they share the names with.
+For example, the ``powersave`` P-state selection algorithm provided by
+``intel_pstate`` is not a counterpart of the generic ``powersave`` governor
+(roughly, it corresponds to the ``schedutil`` and ``ondemand`` governors).
+
+There are two P-state selection algorithms provided by ``intel_pstate`` in the
+active mode: ``powersave`` and ``performance``. The way they both operate
+depends on whether or not the hardware-managed P-states (HWP) feature has been
+enabled in the processor and possibly on the processor model.
+
+Which of the P-state selection algorithms is used by default depends on the
+:c:macro:`CONFIG_CPU_FREQ_DEFAULT_GOV_PERFORMANCE` kernel configuration option.
+Namely, if that option is set, the ``performance`` algorithm will be used by
+default, and the other one will be used by default if it is not set.
+
+Active Mode With HWP
+~~~~~~~~~~~~~~~~~~~~
+
+If the processor supports the HWP feature, it will be enabled during the
+processor initialization and cannot be disabled after that. It is possible
+to avoid enabling it by passing the ``intel_pstate=no_hwp`` argument to the
+kernel in the command line.
+
+If the HWP feature has been enabled, ``intel_pstate`` relies on the processor to
+select P-states by itself, but still it can give hints to the processor's
+internal P-state selection logic. What those hints are depends on which P-state
+selection algorithm has been applied to the given policy (or to the CPU it
+corresponds to).
+
+Even though the P-state selection is carried out by the processor automatically,
+``intel_pstate`` registers utilization update callbacks with the CPU scheduler
+in this mode. However, they are not used for running a P-state selection
+algorithm, but for periodic updates of the current CPU frequency information to
+be made available from the ``scaling_cur_freq`` policy attribute in ``sysfs``.
+
+HWP + ``performance``
+.....................
+
+In this configuration ``intel_pstate`` will write 0 to the processor's
+Energy-Performance Preference (EPP) knob (if supported) or its
+Energy-Performance Bias (EPB) knob (otherwise), wh
git.codelabs.ch / muen / linux.git / commitdiff