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 Signed-off-by: Meng Li li.meng@amd.com --- Documentation/admin-guide/pm/amd-pstate.rst | 59 ++++++++++++++++++++- 1 file changed, 57 insertions(+), 2 deletions(-)
diff --git a/Documentation/admin-guide/pm/amd-pstate.rst b/Documentation/admin-guide/pm/amd-pstate.rst index 1cf40f69278c..0b832ff529db 100644 --- a/Documentation/admin-guide/pm/amd-pstate.rst +++ b/Documentation/admin-guide/pm/amd-pstate.rst @@ -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`` ===============================================