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Documentation: amd-pstate: introduce amd-pstate preferred core

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Introduce amd-pstate preferred core.

check preferred core state set by the kernel parameter:
$ cat /sys/devices/system/cpu/amd-pstate/prefcore

Tested-by: Oleksandr Natalenko <oleksandr@natalenko.name>
Reviewed-by: Wyes Karny <wyes.karny@amd.com>
Reviewed-by: Mario Limonciello <mario.limonciello@amd.com>
Reviewed-by: Huang Rui <ray.huang@amd.com>
Reviewed-by: Perry Yuan <perry.yuan@amd.com>
Signed-off-by: Meng Li <li.meng@amd.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
This commit is contained in:
Meng Li 2024-01-19 17:05:01 +08:00 committed by Rafael J. Wysocki
parent e571a5e206
commit 3a004e1fee
1 changed files with 57 additions and 2 deletions
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59
Documentation/admin-guide/pm/amd-pstate.rst
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@ -300,8 +300,8 @@ platforms. The AMD P-States mechanism is the more performance and energy
efficiency frequency management method on AMD processors.
AMD Pstate Driver Operation Modes
=================================
``amd-pstate`` Driver Operation Modes
======================================
``amd_pstate`` CPPC has 3 operation modes: autonomous (active) mode,
non-autonomous (passive) mode and guided autonomous (guided) mode.
@ -353,6 +353,48 @@ is activated. In this mode, driver requests minimum and maximum performance
level and the platform autonomously selects a performance level in this range
and appropriate to the current workload.
``amd-pstate`` Preferred Core
=================================
The core frequency is subjected to the process variation in semiconductors.
Not all cores are able to reach the maximum frequency respecting the
infrastructure limits. Consequently, AMD has redefined the concept of
maximum frequency of a part. This means that a fraction of cores can reach
maximum frequency. To find the best process scheduling policy for a given
scenario, OS needs to know the core ordering informed by the platform through
highest performance capability register of the CPPC interface.
``amd-pstate`` preferred core enables the scheduler to prefer scheduling on
cores that can achieve a higher frequency with lower voltage. The preferred
core rankings can dynamically change based on the workload, platform conditions,
thermals and ageing.
The priority metric will be initialized by the ``amd-pstate`` driver. The ``amd-pstate``
driver will also determine whether or not ``amd-pstate`` preferred core is
supported by the platform.
``amd-pstate`` driver will provide an initial core ordering when the system boots.
The platform uses the CPPC interfaces to communicate the core ranking to the
operating system and scheduler to make sure that OS is choosing the cores
with highest performance firstly for scheduling the process. When ``amd-pstate``
driver receives a message with the highest performance change, it will
update the core ranking and set the cpu's priority.
``amd-pstate`` Preferred Core Switch
=================================
Kernel Parameters
-----------------
``amd-pstate`` peferred core`` has two states: enable and disable.
Enable/disable states can be chosen by different kernel parameters.
Default enable ``amd-pstate`` preferred core.
``amd_prefcore=disable``
For systems that support ``amd-pstate`` preferred core, the core rankings will
always be advertised by the platform. But OS can choose to ignore that via the
kernel parameter ``amd_prefcore=disable``.
User Space Interface in ``sysfs`` - General
===========================================
@ -385,6 +427,19 @@ control its functionality at the system level. They are located in the
to the operation mode represented by that string - or to be
unregistered in the "disable" case.
``prefcore``
Preferred core state of the driver: "enabled" or "disabled".
"enabled"
Enable the ``amd-pstate`` preferred core.
"disabled"
Disable the ``amd-pstate`` preferred core
This attribute is read-only to check the state of preferred core set
by the kernel parameter.
``cpupower`` tool support for ``amd-pstate``
===============================================