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Documentation/amd-pstate: Update dynamic_epp documentation with new behavior

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Update the admin-guide for dynamic_epp describing the latest integration
into energy_performance_preference selections.

Signed-off-by: K Prateek Nayak <kprateek.nayak@amd.com>
Link: https://lore.kernel.org/r/20260727072056.1248-7-kprateek.nayak@amd.com
Signed-off-by: Mario Limonciello <superm1@kernel.org>
This commit is contained in:
K Prateek Nayak
2026-07-27 07:20:53 +00:00
committed by Mario Limonciello
parent 32692fcf61
commit d3a019bd08
1 changed files with 20 additions and 21 deletions
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41
Documentation/admin-guide/pm/amd-pstate.rst
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@@ -317,7 +317,9 @@ These profiles represent different hints that are provided
to the low-level firmware about the user's desired energy vs efficiency
tradeoff. ``default`` represents the epp value is set by platform
firmware. ``custom`` designates that integer values 0-255 may be written
as well. This attribute is read-only.
as well. ``dynamic`` designates that the EPP is modified dynamically
on kernel events. See ``Dynamic energy performance profile`` section below to
know more about the ``dynamic`` mode. This attribute is read-only.
``energy_performance_preference``
@@ -326,13 +328,11 @@ and user can change current preference according to energy or performance needs
Coarse named profiles are available in the attribute
``energy_performance_available_preferences``.
Users can also write individual integer values between 0 to 255.
When dynamic EPP is enabled, writes to energy_performance_preference are blocked
even when EPP feature is enabled by platform firmware. Lower epp values shift the bias
towards improved performance while a higher epp value shifts the bias towards
power-savings. The exact impact can change from one platform to the other.
If a valid integer was last written, then a number will be returned on future reads.
If a valid string was last written then a string will be returned on future reads.
This attribute is read-write.
Lower epp values shift the bias towards improved performance while a higher epp
value shifts the bias towards power-savings. The exact impact can change from
one platform to the other. If a valid integer was last written, then a number
will be returned on future reads. If a valid string was last written then a
string will be returned on future reads. This attribute is read-write.
``boost``
The `boost` sysfs attribute provides control over the CPU core
@@ -356,21 +356,20 @@ Other performance and frequency values can be read back from
Dynamic energy performance profile
==================================
The amd-pstate driver supports dynamically selecting the energy performance
profile based on whether the machine is running on AC or DC power.
profile based on the system profile and the current power source in active mode.
Whether this behavior is enabled by default depends on the kernel command line option
``amd_dynamic_epp`` is set. This behavior can also be overridden
at runtime by the sysfs file ``/sys/devices/system/cpu/amd_pstate/dynamic_epp``.
The ``dynamic`` mode is listed in
``/sys/devices/system/cpu/cpuX/cpufreq/energy_performance_available_preferences``
when available while running under the ``powersave`` governor. The ``dynamic``
mode can be toggled on by writing the same to the sysfs file
``/sys/devices/system/cpu/cpuX/cpufreq/energy_performance_preference`` when
available.
When set to enabled, the driver will select a different energy performance
profile when the machine is running on battery or AC power. The driver will
also register with the platform profile handler to receive notifications of
user desired power state and react to those.
When set to disabled, the driver will not change the energy performance profile
based on the power source and will not react to user desired power state.
Attempting to manually write to the ``energy_performance_preference`` sysfs
file will fail when ``dynamic_epp`` is enabled.
When ``energy_performance_preference`` is set to ``dynamic``, the driver will
select a different energy performance profile when the machine is running on
battery or AC power. The driver will also register with the platform profile
handler to receive notifications of user desired power state and react to
those.
``amd-pstate`` vs ``acpi-cpufreq``
======================================