diff mbox series

[V5,6/7] Documentation: amd-pstate: introduce amd-pstate preferred core

Message ID 20230905015116.2268926-7-li.meng@amd.com
State Superseded
Headers show
Series [V5,1/7] x86: Drop CPU_SUP_INTEL from SCHED_MC_PRIO for the expansion. | expand

Commit Message

Meng, Li (Jassmine) Sept. 5, 2023, 1:51 a.m. UTC
Introduce amd-pstate preferred core.

check hardware preferred core state:
$ cat /sys/devices/system/cpu/amd-pstate/hw_prefcore
check preferred core state:
$ cat /sys/devices/system/cpu/amd-pstate/prefcore

Signed-off-by: Meng Li <li.meng@amd.com>
---
 Documentation/admin-guide/pm/amd-pstate.rst | 68 ++++++++++++++++++++-
 1 file changed, 67 insertions(+), 1 deletion(-)

Comments

kernel test robot Sept. 6, 2023, 10:01 p.m. UTC | #1
Hi Meng,

kernel test robot noticed the following build warnings:

[auto build test WARNING on rafael-pm/linux-next]
[also build test WARNING on linus/master v6.5 next-20230906]
[cannot apply to tip/x86/core]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Meng-Li/x86-Drop-CPU_SUP_INTEL-from-SCHED_MC_PRIO-for-the-expansion/20230906-003754
base:   https://git.kernel.org/pub/scm/linux/kernel/git/rafael/linux-pm.git linux-next
patch link:    https://lore.kernel.org/r/20230905015116.2268926-7-li.meng%40amd.com
patch subject: [PATCH V5 6/7] Documentation: amd-pstate: introduce amd-pstate preferred core
reproduce: (https://download.01.org/0day-ci/archive/20230907/202309070502.YxzVpYTO-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202309070502.YxzVpYTO-lkp@intel.com/

All warnings (new ones prefixed by >>):

>> Documentation/admin-guide/pm/amd-pstate.rst:304: WARNING: Title underline too short.

vim +304 Documentation/admin-guide/pm/amd-pstate.rst

c22760885fd6f7 Huang Rui  2021-12-24  301  
92e6088427c5da Perry Yuan 2023-01-31  302  
3a7b575560efa6 Meng Li    2023-09-05  303  ``amd-pstate`` Driver Operation Modes
92e6088427c5da Perry Yuan 2023-01-31 @304  =================================
92e6088427c5da Perry Yuan 2023-01-31  305
diff mbox series

Patch

diff --git a/Documentation/admin-guide/pm/amd-pstate.rst b/Documentation/admin-guide/pm/amd-pstate.rst
index 1cf40f69278c..204f5d49d47d 100644
--- a/Documentation/admin-guide/pm/amd-pstate.rst
+++ b/Documentation/admin-guide/pm/amd-pstate.rst
@@ -300,7 +300,7 @@  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,
@@ -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 +427,30 @@  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.
 
+``hw_prefcore``
+	Preferred core state of hardware: "supported" or "unsupported".
+
+	"supported"
+		The processor and power firmware support preferred core.
+
+	"unsupported"
+		The processor and power firmware don't support preferred core.
+
+
+        This attribute is read-only to check the state of hardware preferred core.
+
+``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.
+
 ``cpupower`` tool support for ``amd-pstate``
 ===============================================