Merge branch 'pm-cpufreq'
* pm-cpufreq: cpufreq: intel_pstate: Implement passive mode with HWP enabled
This commit is contained in:
@@ -54,10 +54,13 @@ registered (see `below <status_attr_>`_).
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Operation Modes
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===============
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``intel_pstate`` can operate in three different modes: in the active mode with
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or without hardware-managed P-states support and in the passive mode. Which of
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them will be in effect depends on what kernel command line options are used and
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on the capabilities of the processor.
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``intel_pstate`` can operate in two different modes, active or passive. In the
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active mode, it uses its own internal performance scaling governor algorithm or
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allows the hardware to do preformance scaling by itself, while in the passive
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mode it responds to requests made by a generic ``CPUFreq`` governor implementing
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a certain performance scaling algorithm. Which of them will be in effect
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depends on what kernel command line options are used and on the capabilities of
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the processor.
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Active Mode
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-----------
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@@ -194,10 +197,11 @@ This is the default operation mode of ``intel_pstate`` for processors without
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hardware-managed P-states (HWP) support. It is always used if the
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``intel_pstate=passive`` argument is passed to the kernel in the command line
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regardless of whether or not the given processor supports HWP. [Note that the
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``intel_pstate=no_hwp`` setting implies ``intel_pstate=passive`` if it is used
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without ``intel_pstate=active``.] Like in the active mode without HWP support,
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in this mode ``intel_pstate`` may refuse to work with processors that are not
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recognized by it.
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``intel_pstate=no_hwp`` setting causes the driver to start in the passive mode
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if it is not combined with ``intel_pstate=active``.] Like in the active mode
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without HWP support, in this mode ``intel_pstate`` may refuse to work with
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processors that are not recognized by it if HWP is prevented from being enabled
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through the kernel command line.
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If the driver works in this mode, the ``scaling_driver`` policy attribute in
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``sysfs`` for all ``CPUFreq`` policies contains the string "intel_cpufreq".
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@@ -318,10 +322,9 @@ manuals need to be consulted to get to it too.
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For this reason, there is a list of supported processors in ``intel_pstate`` and
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the driver initialization will fail if the detected processor is not in that
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list, unless it supports the `HWP feature <Active Mode_>`_. [The interface to
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obtain all of the information listed above is the same for all of the processors
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supporting the HWP feature, which is why they all are supported by
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``intel_pstate``.]
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list, unless it supports the HWP feature. [The interface to obtain all of the
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information listed above is the same for all of the processors supporting the
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HWP feature, which is why ``intel_pstate`` works with all of them.]
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User Space Interface in ``sysfs``
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@@ -425,22 +428,16 @@ argument is passed to the kernel in the command line.
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as well as the per-policy ones) are then reset to their default
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values, possibly depending on the target operation mode.]
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That only is supported in some configurations, though (for example, if
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the `HWP feature is enabled in the processor <Active Mode With HWP_>`_,
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the operation mode of the driver cannot be changed), and if it is not
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supported in the current configuration, writes to this attribute will
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fail with an appropriate error.
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``energy_efficiency``
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This attribute is only present on platforms, which have CPUs matching
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Kaby Lake or Coffee Lake desktop CPU model. By default
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energy efficiency optimizations are disabled on these CPU models in HWP
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mode by this driver. Enabling energy efficiency may limit maximum
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operating frequency in both HWP and non HWP mode. In non HWP mode,
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optimizations are done only in the turbo frequency range. In HWP mode,
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optimizations are done in the entire frequency range. Setting this
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attribute to "1" enables energy efficiency optimizations and setting
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to "0" disables energy efficiency optimizations.
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This attribute is only present on platforms with CPUs matching the Kaby
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Lake or Coffee Lake desktop CPU model. By default, energy-efficiency
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optimizations are disabled on these CPU models if HWP is enabled.
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Enabling energy-efficiency optimizations may limit maximum operating
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frequency with or without the HWP feature. With HWP enabled, the
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optimizations are done only in the turbo frequency range. Without it,
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they are done in the entire available frequency range. Setting this
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attribute to "1" enables the energy-efficiency optimizations and setting
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to "0" disables them.
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Interpretation of Policy Attributes
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-----------------------------------
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@@ -484,8 +481,8 @@ Next, the following policy attributes have special meaning if
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policy for the time interval between the last two invocations of the
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driver's utilization update callback by the CPU scheduler for that CPU.
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One more policy attribute is present if the `HWP feature is enabled in the
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processor <Active Mode With HWP_>`_:
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One more policy attribute is present if the HWP feature is enabled in the
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processor:
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``base_frequency``
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Shows the base frequency of the CPU. Any frequency above this will be
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@@ -526,11 +523,11 @@ on the following rules, regardless of the current operation mode of the driver:
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3. The global and per-policy limits can be set independently.
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If the `HWP feature is enabled in the processor <Active Mode With HWP_>`_, the
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resulting effective values are written into its registers whenever the limits
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change in order to request its internal P-state selection logic to always set
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P-states within these limits. Otherwise, the limits are taken into account by
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scaling governors (in the `passive mode <Passive Mode_>`_) and by the driver
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In the `active mode with the HWP feature enabled <Active Mode With HWP_>`_, the
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resulting effective values are written into hardware registers whenever the
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limits change in order to request its internal P-state selection logic to always
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set P-states within these limits. Otherwise, the limits are taken into account
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by scaling governors (in the `passive mode <Passive Mode_>`_) and by the driver
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every time before setting a new P-state for a CPU.
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Additionally, if the ``intel_pstate=per_cpu_perf_limits`` command line argument
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@@ -541,12 +538,11 @@ at all and the only way to set the limits is by using the policy attributes.
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Energy vs Performance Hints
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---------------------------
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If ``intel_pstate`` works in the `active mode with the HWP feature enabled
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<Active Mode With HWP_>`_ in the processor, additional attributes are present
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in every ``CPUFreq`` policy directory in ``sysfs``. They are intended to allow
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user space to help ``intel_pstate`` to adjust the processor's internal P-state
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selection logic by focusing it on performance or on energy-efficiency, or
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somewhere between the two extremes:
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If the hardware-managed P-states (HWP) is enabled in the processor, additional
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attributes, intended to allow user space to help ``intel_pstate`` to adjust the
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processor's internal P-state selection logic by focusing it on performance or on
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energy-efficiency, or somewhere between the two extremes, are present in every
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``CPUFreq`` policy directory in ``sysfs``. They are :
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``energy_performance_preference``
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Current value of the energy vs performance hint for the given policy
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@@ -650,12 +646,14 @@ of them have to be prepended with the ``intel_pstate=`` prefix.
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Do not register ``intel_pstate`` as the scaling driver even if the
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processor is supported by it.
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``active``
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Register ``intel_pstate`` in the `active mode <Active Mode_>`_ to start
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with.
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``passive``
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Register ``intel_pstate`` in the `passive mode <Passive Mode_>`_ to
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start with.
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This option implies the ``no_hwp`` one described below.
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``force``
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Register ``intel_pstate`` as the scaling driver instead of
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``acpi-cpufreq`` even if the latter is preferred on the given system.
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@@ -670,13 +668,12 @@ of them have to be prepended with the ``intel_pstate=`` prefix.
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driver is used instead of ``acpi-cpufreq``.
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``no_hwp``
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Do not enable the `hardware-managed P-states (HWP) feature
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<Active Mode With HWP_>`_ even if it is supported by the processor.
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Do not enable the hardware-managed P-states (HWP) feature even if it is
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supported by the processor.
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``hwp_only``
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Register ``intel_pstate`` as the scaling driver only if the
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`hardware-managed P-states (HWP) feature <Active Mode With HWP_>`_ is
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supported by the processor.
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hardware-managed P-states (HWP) feature is supported by the processor.
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``support_acpi_ppc``
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Take ACPI ``_PPC`` performance limits into account.
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