Adding upstream version 6.1.76.upstream/6.1.76upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

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+.. SPDX-License-Identifier: GPL-2.0
+.. include:: <isonum.txt>
+
+===============================================
+``amd-pstate`` CPU Performance Scaling Driver
+===============================================
+
+:Copyright: |copy| 2021 Advanced Micro Devices, Inc.
+
+:Author: Huang Rui <ray.huang@amd.com>
+
+
+Introduction
+===================
+
+``amd-pstate`` is the AMD CPU performance scaling driver that introduces a
+new CPU frequency control mechanism on modern AMD APU and CPU series in
+Linux kernel. The new mechanism is based on Collaborative Processor
+Performance Control (CPPC) which provides finer grain frequency management
+than legacy ACPI hardware P-States. Current AMD CPU/APU platforms are using
+the ACPI P-states driver to manage CPU frequency and clocks with switching
+only in 3 P-states. CPPC replaces the ACPI P-states controls and allows a
+flexible, low-latency interface for the Linux kernel to directly
+communicate the performance hints to hardware.
+
+``amd-pstate`` leverages the Linux kernel governors such as ``schedutil``,
+``ondemand``, etc. to manage the performance hints which are provided by
+CPPC hardware functionality that internally follows the hardware
+specification (for details refer to AMD64 Architecture Programmer's Manual
+Volume 2: System Programming [1]_). Currently, ``amd-pstate`` supports basic
+frequency control function according to kernel governors on some of the
+Zen2 and Zen3 processors, and we will implement more AMD specific functions
+in future after we verify them on the hardware and SBIOS.
+
+
+AMD CPPC Overview
+=======================
+
+Collaborative Processor Performance Control (CPPC) interface enumerates a
+continuous, abstract, and unit-less performance value in a scale that is
+not tied to a specific performance state / frequency. This is an ACPI
+standard [2]_ which software can specify application performance goals and
+hints as a relative target to the infrastructure limits. AMD processors
+provide the low latency register model (MSR) instead of an AML code
+interpreter for performance adjustments. ``amd-pstate`` will initialize a
+``struct cpufreq_driver`` instance, ``amd_pstate_driver``, with the callbacks
+to manage each performance update behavior. ::
+
+ Highest Perf ------>+-----------------------+                         +-----------------------+
+                     |                       |                         |                       |
+                     |                       |                         |                       |
+                     |                       |          Max Perf  ---->|                       |
+                     |                       |                         |                       |
+                     |                       |                         |                       |
+ Nominal Perf ------>+-----------------------+                         +-----------------------+
+                     |                       |                         |                       |
+                     |                       |                         |                       |
+                     |                       |                         |                       |
+                     |                       |                         |                       |
+                     |                       |                         |                       |
+                     |                       |                         |                       |
+                     |                       |      Desired Perf  ---->|                       |
+                     |                       |                         |                       |
+                     |                       |                         |                       |
+                     |                       |                         |                       |
+                     |                       |                         |                       |
+                     |                       |                         |                       |
+                     |                       |                         |                       |
+                     |                       |                         |                       |
+                     |                       |                         |                       |
+                     |                       |                         |                       |
+  Lowest non-        |                       |                         |                       |
+  linear perf ------>+-----------------------+                         +-----------------------+
+                     |                       |                         |                       |
+                     |                       |       Lowest perf  ---->|                       |
+                     |                       |                         |                       |
+  Lowest perf ------>+-----------------------+                         +-----------------------+
+                     |                       |                         |                       |
+                     |                       |                         |                       |
+                     |                       |                         |                       |
+          0   ------>+-----------------------+                         +-----------------------+
+
+                                     AMD P-States Performance Scale
+
+
+.. _perf_cap:
+
+AMD CPPC Performance Capability
+--------------------------------
+
+Highest Performance (RO)
+.........................
+
+This is the absolute maximum performance an individual processor may reach,
+assuming ideal conditions. This performance level may not be sustainable
+for long durations and may only be achievable if other platform components
+are in a specific state; for example, it may require other processors to be in
+an idle state. This would be equivalent to the highest frequencies
+supported by the processor.
+
+Nominal (Guaranteed) Performance (RO)
+......................................
+
+This is the maximum sustained performance level of the processor, assuming
+ideal operating conditions. In the absence of an external constraint (power,
+thermal, etc.), this is the performance level the processor is expected to
+be able to maintain continuously. All cores/processors are expected to be
+able to sustain their nominal performance state simultaneously.
+
+Lowest non-linear Performance (RO)
+...................................
+
+This is the lowest performance level at which nonlinear power savings are
+achieved, for example, due to the combined effects of voltage and frequency
+scaling. Above this threshold, lower performance levels should be generally
+more energy efficient than higher performance levels. This register
+effectively conveys the most efficient performance level to ``amd-pstate``.
+
+Lowest Performance (RO)
+........................
+
+This is the absolute lowest performance level of the processor. Selecting a
+performance level lower than the lowest nonlinear performance level may
+cause an efficiency penalty but should reduce the instantaneous power
+consumption of the processor.
+
+AMD CPPC Performance Control
+------------------------------
+
+``amd-pstate`` passes performance goals through these registers. The
+register drives the behavior of the desired performance target.
+
+Minimum requested performance (RW)
+...................................
+
+``amd-pstate`` specifies the minimum allowed performance level.
+
+Maximum requested performance (RW)
+...................................
+
+``amd-pstate`` specifies a limit the maximum performance that is expected
+to be supplied by the hardware.
+
+Desired performance target (RW)
+...................................
+
+``amd-pstate`` specifies a desired target in the CPPC performance scale as
+a relative number. This can be expressed as percentage of nominal
+performance (infrastructure max). Below the nominal sustained performance
+level, desired performance expresses the average performance level of the
+processor subject to hardware. Above the nominal performance level,
+the processor must provide at least nominal performance requested and go higher
+if current operating conditions allow.
+
+Energy Performance Preference (EPP) (RW)
+.........................................
+
+This attribute provides a hint to the hardware if software wants to bias
+toward performance (0x0) or energy efficiency (0xff).
+
+
+Key Governors Support
+=======================
+
+``amd-pstate`` can be used with all the (generic) scaling governors listed
+by the ``scaling_available_governors`` policy attribute in ``sysfs``. Then,
+it is responsible for the configuration of policy objects corresponding to
+CPUs and provides the ``CPUFreq`` core (and the scaling governors attached
+to the policy objects) with accurate information on the maximum and minimum
+operating frequencies supported by the hardware. Users can check the
+``scaling_cur_freq`` information comes from the ``CPUFreq`` core.
+
+``amd-pstate`` mainly supports ``schedutil`` and ``ondemand`` for dynamic
+frequency control. It is to fine tune the processor configuration on
+``amd-pstate`` to the ``schedutil`` with CPU CFS scheduler. ``amd-pstate``
+registers the adjust_perf callback to implement performance update behavior
+similar to CPPC. It is initialized by ``sugov_start`` and then populates the
+CPU's update_util_data pointer to assign ``sugov_update_single_perf`` as the
+utilization update callback function in the CPU scheduler. The CPU scheduler
+will call ``cpufreq_update_util`` and assigns the target performance according
+to the ``struct sugov_cpu`` that the utilization update belongs to.
+Then, ``amd-pstate`` updates the desired performance according to the CPU
+scheduler assigned.
+
+.. _processor_support:
+
+Processor Support
+=======================
+
+The ``amd-pstate`` initialization will fail if the ``_CPC`` entry in the ACPI
+SBIOS does not exist in the detected processor. It uses ``acpi_cpc_valid``
+to check the existence of ``_CPC``. All Zen based processors support the legacy
+ACPI hardware P-States function, so when ``amd-pstate`` fails initialization,
+the kernel will fall back to initialize the ``acpi-cpufreq`` driver.
+
+There are two types of hardware implementations for ``amd-pstate``: one is
+`Full MSR Support <perf_cap_>`_ and another is `Shared Memory Support
+<perf_cap_>`_. It can use the :c:macro:`X86_FEATURE_CPPC` feature flag to
+indicate the different types. (For details, refer to the Processor Programming
+Reference (PPR) for AMD Family 19h Model 51h, Revision A1 Processors [3]_.)
+``amd-pstate`` is to register different ``static_call`` instances for different
+hardware implementations.
+
+Currently, some of the Zen2 and Zen3 processors support ``amd-pstate``. In the
+future, it will be supported on more and more AMD processors.
+
+Full MSR Support
+-----------------
+
+Some new Zen3 processors such as Cezanne provide the MSR registers directly
+while the :c:macro:`X86_FEATURE_CPPC` CPU feature flag is set.
+``amd-pstate`` can handle the MSR register to implement the fast switch
+function in ``CPUFreq`` that can reduce the latency of frequency control in
+interrupt context. The functions with a ``pstate_xxx`` prefix represent the
+operations on MSR registers.
+
+Shared Memory Support
+----------------------
+
+If the :c:macro:`X86_FEATURE_CPPC` CPU feature flag is not set, the
+processor supports the shared memory solution. In this case, ``amd-pstate``
+uses the ``cppc_acpi`` helper methods to implement the callback functions
+that are defined on ``static_call``. The functions with the ``cppc_xxx`` prefix
+represent the operations of ACPI CPPC helpers for the shared memory solution.
+
+
+AMD P-States and ACPI hardware P-States always can be supported in one
+processor. But AMD P-States has the higher priority and if it is enabled
+with :c:macro:`MSR_AMD_CPPC_ENABLE` or ``cppc_set_enable``, it will respond
+to the request from AMD P-States.
+
+
+User Space Interface in ``sysfs``
+==================================
+
+``amd-pstate`` exposes several global attributes (files) in ``sysfs`` to
+control its functionality at the system level. They are located in the
+``/sys/devices/system/cpu/cpufreq/policyX/`` directory and affect all CPUs. ::
+
+ root@hr-test1:/home/ray# ls /sys/devices/system/cpu/cpufreq/policy0/*amd*
+ /sys/devices/system/cpu/cpufreq/policy0/amd_pstate_highest_perf
+ /sys/devices/system/cpu/cpufreq/policy0/amd_pstate_lowest_nonlinear_freq
+ /sys/devices/system/cpu/cpufreq/policy0/amd_pstate_max_freq
+
+
+``amd_pstate_highest_perf / amd_pstate_max_freq``
+
+Maximum CPPC performance and CPU frequency that the driver is allowed to
+set, in percent of the maximum supported CPPC performance level (the highest
+performance supported in `AMD CPPC Performance Capability <perf_cap_>`_).
+In some ASICs, the highest CPPC performance is not the one in the ``_CPC``
+table, so we need to expose it to sysfs. If boost is not active, but
+still supported, this maximum frequency will be larger than the one in
+``cpuinfo``.
+This attribute is read-only.
+
+``amd_pstate_lowest_nonlinear_freq``
+
+The lowest non-linear CPPC CPU frequency that the driver is allowed to set,
+in percent of the maximum supported CPPC performance level. (Please see the
+lowest non-linear performance in `AMD CPPC Performance Capability
+<perf_cap_>`_.)
+This attribute is read-only.
+
+Other performance and frequency values can be read back from
+``/sys/devices/system/cpu/cpuX/acpi_cppc/``, see :ref:`cppc_sysfs`.
+
+
+``amd-pstate`` vs ``acpi-cpufreq``
+======================================
+
+On the majority of AMD platforms supported by ``acpi-cpufreq``, the ACPI tables
+provided by the platform firmware are used for CPU performance scaling, but
+only provide 3 P-states on AMD processors.
+However, on modern AMD APU and CPU series, hardware provides the Collaborative
+Processor Performance Control according to the ACPI protocol and customizes this
+for AMD platforms. That is, fine-grained and continuous frequency ranges
+instead of the legacy hardware P-states. ``amd-pstate`` is the kernel
+module which supports the new AMD P-States mechanism on most of the future AMD
+platforms. The AMD P-States mechanism is the more performance and energy
+efficiency frequency management method on AMD processors.
+
+Kernel Module Options for ``amd-pstate``
+=========================================
+
+Passive Mode
+------------
+
+``amd_pstate=passive``
+
+It will be enabled if the ``amd_pstate=passive`` is passed to the kernel in the command line.
+In this mode, ``amd_pstate`` driver software specifies a desired QoS target in the CPPC
+performance scale as a relative number. This can be expressed as percentage of nominal
+performance (infrastructure max). Below the nominal sustained performance level,
+desired performance expresses the average performance level of the processor subject
+to the Performance Reduction Tolerance register. Above the nominal performance level,
+processor must provide at least nominal performance requested and go higher if current
+operating conditions allow.
+
+
+``cpupower`` tool support for ``amd-pstate``
+===============================================
+
+``amd-pstate`` is supported by the ``cpupower`` tool, which can be used to dump
+frequency information. Development is in progress to support more and more
+operations for the new ``amd-pstate`` module with this tool. ::
+
+ root@hr-test1:/home/ray# cpupower frequency-info
+ analyzing CPU 0:
+   driver: amd-pstate
+   CPUs which run at the same hardware frequency: 0
+   CPUs which need to have their frequency coordinated by software: 0
+   maximum transition latency: 131 us
+   hardware limits: 400 MHz - 4.68 GHz
+   available cpufreq governors: ondemand conservative powersave userspace performance schedutil
+   current policy: frequency should be within 400 MHz and 4.68 GHz.
+                   The governor "schedutil" may decide which speed to use
+                   within this range.
+   current CPU frequency: Unable to call hardware
+   current CPU frequency: 4.02 GHz (asserted by call to kernel)
+   boost state support:
+     Supported: yes
+     Active: yes
+     AMD PSTATE Highest Performance: 166. Maximum Frequency: 4.68 GHz.
+     AMD PSTATE Nominal Performance: 117. Nominal Frequency: 3.30 GHz.
+     AMD PSTATE Lowest Non-linear Performance: 39. Lowest Non-linear Frequency: 1.10 GHz.
+     AMD PSTATE Lowest Performance: 15. Lowest Frequency: 400 MHz.
+
+
+Diagnostics and Tuning
+=======================
+
+Trace Events
+--------------
+
+There are two static trace events that can be used for ``amd-pstate``
+diagnostics. One of them is the ``cpu_frequency`` trace event generally used
+by ``CPUFreq``, and the other one is the ``amd_pstate_perf`` trace event
+specific to ``amd-pstate``.  The following sequence of shell commands can
+be used to enable them and see their output (if the kernel is
+configured to support event tracing). ::
+
+ root@hr-test1:/home/ray# cd /sys/kernel/tracing/
+ root@hr-test1:/sys/kernel/tracing# echo 1 > events/amd_cpu/enable
+ root@hr-test1:/sys/kernel/tracing# cat trace
+ # tracer: nop
+ #
+ # entries-in-buffer/entries-written: 47827/42233061   #P:2
+ #
+ #                                _-----=> irqs-off
+ #                               / _----=> need-resched
+ #                              | / _---=> hardirq/softirq
+ #                              || / _--=> preempt-depth
+ #                              ||| /     delay
+ #           TASK-PID     CPU#  ||||   TIMESTAMP  FUNCTION
+ #              | |         |   ||||      |         |
+          <idle>-0       [015] dN...  4995.979886: amd_pstate_perf: amd_min_perf=85 amd_des_perf=85 amd_max_perf=166 cpu_id=15 changed=false fast_switch=true
+          <idle>-0       [007] d.h..  4995.979893: amd_pstate_perf: amd_min_perf=85 amd_des_perf=85 amd_max_perf=166 cpu_id=7 changed=false fast_switch=true
+             cat-2161    [000] d....  4995.980841: amd_pstate_perf: amd_min_perf=85 amd_des_perf=85 amd_max_perf=166 cpu_id=0 changed=false fast_switch=true
+            sshd-2125    [004] d.s..  4995.980968: amd_pstate_perf: amd_min_perf=85 amd_des_perf=85 amd_max_perf=166 cpu_id=4 changed=false fast_switch=true
+          <idle>-0       [007] d.s..  4995.980968: amd_pstate_perf: amd_min_perf=85 amd_des_perf=85 amd_max_perf=166 cpu_id=7 changed=false fast_switch=true
+          <idle>-0       [003] d.s..  4995.980971: amd_pstate_perf: amd_min_perf=85 amd_des_perf=85 amd_max_perf=166 cpu_id=3 changed=false fast_switch=true
+          <idle>-0       [011] d.s..  4995.980996: amd_pstate_perf: amd_min_perf=85 amd_des_perf=85 amd_max_perf=166 cpu_id=11 changed=false fast_switch=true
+
+The ``cpu_frequency`` trace event will be triggered either by the ``schedutil`` scaling
+governor (for the policies it is attached to), or by the ``CPUFreq`` core (for the
+policies with other scaling governors).
+
+
+Tracer Tool
+-------------
+
+``amd_pstate_tracer.py`` can record and parse ``amd-pstate`` trace log, then
+generate performance plots. This utility can be used to debug and tune the
+performance of ``amd-pstate`` driver. The tracer tool needs to import intel
+pstate tracer.
+
+Tracer tool located in ``linux/tools/power/x86/amd_pstate_tracer``. It can be
+used in two ways. If trace file is available, then directly parse the file
+with command ::
+
+ ./amd_pstate_trace.py [-c cpus] -t <trace_file> -n <test_name>
+
+Or generate trace file with root privilege, then parse and plot with command ::
+
+ sudo ./amd_pstate_trace.py [-c cpus] -n <test_name> -i <interval> [-m kbytes]
+
+The test result can be found in ``results/test_name``. Following is the example
+about part of the output. ::
+
+ common_cpu  common_secs  common_usecs  min_perf  des_perf  max_perf  freq    mperf   apef    tsc       load   duration_ms  sample_num  elapsed_time  common_comm
+ CPU_005     712          116384        39        49        166       0.7565  9645075 2214891 38431470  25.1   11.646       469         2.496         kworker/5:0-40
+ CPU_006     712          116408        39        49        166       0.6769  8950227 1839034 37192089  24.06  11.272       470         2.496         kworker/6:0-1264
+
+Unit Tests for amd-pstate
+-------------------------
+
+``amd-pstate-ut`` is a test module for testing the ``amd-pstate`` driver.
+
+ * It can help all users to verify their processor support (SBIOS/Firmware or Hardware).
+
+ * Kernel can have a basic function test to avoid the kernel regression during the update.
+
+ * We can introduce more functional or performance tests to align the result together, it will benefit power and performance scale optimization.
+
+1. Test case decriptions
+
+        +---------+--------------------------------+------------------------------------------------------------------------------------+
+        | Index   | Functions                      | Description                                                                        |
+        +=========+================================+====================================================================================+
+        | 0       | amd_pstate_ut_acpi_cpc_valid   || Check whether the _CPC object is present in SBIOS.                                |
+        |         |                                ||                                                                                   |
+        |         |                                || The detail refer to `Processor Support <processor_support_>`_.                    |
+        +---------+--------------------------------+------------------------------------------------------------------------------------+
+        | 1       | amd_pstate_ut_check_enabled    || Check whether AMD P-State is enabled.                                             |
+        |         |                                ||                                                                                   |
+        |         |                                || AMD P-States and ACPI hardware P-States always can be supported in one processor. |
+        |         |                                | But AMD P-States has the higher priority and if it is enabled with                 |
+        |         |                                | :c:macro:`MSR_AMD_CPPC_ENABLE` or ``cppc_set_enable``, it will respond to the      |
+        |         |                                | request from AMD P-States.                                                         |
+        +---------+--------------------------------+------------------------------------------------------------------------------------+
+        | 2       | amd_pstate_ut_check_perf       || Check if the each performance values are reasonable.                              |
+        |         |                                || highest_perf >= nominal_perf > lowest_nonlinear_perf > lowest_perf > 0.           |
+        +---------+--------------------------------+------------------------------------------------------------------------------------+
+        | 3       | amd_pstate_ut_check_freq       || Check if the each frequency values and max freq when set support boost mode       |
+        |         |                                | are reasonable.                                                                    |
+        |         |                                || max_freq >= nominal_freq > lowest_nonlinear_freq > min_freq > 0                   |
+        |         |                                || If boost is not active but supported, this maximum frequency will be larger than  |
+        |         |                                | the one in ``cpuinfo``.                                                            |
+        +---------+--------------------------------+------------------------------------------------------------------------------------+
+
+#. How to execute the tests
+
+   We use test module in the kselftest frameworks to implement it.
+   We create amd-pstate-ut module and tie it into kselftest.(for
+   details refer to Linux Kernel Selftests [4]_).
+
+    1. Build
+
+        + open the :c:macro:`CONFIG_X86_AMD_PSTATE` configuration option.
+        + set the :c:macro:`CONFIG_X86_AMD_PSTATE_UT` configuration option to M.
+        + make project
+        + make selftest ::
+
+            $ cd linux
+            $ make -C tools/testing/selftests
+
+    #. Installation & Steps ::
+
+        $ make -C tools/testing/selftests install INSTALL_PATH=~/kselftest
+        $ sudo ./kselftest/run_kselftest.sh -c amd-pstate
+        TAP version 13
+        1..1
+        # selftests: amd-pstate: amd-pstate-ut.sh
+        # amd-pstate-ut: ok
+        ok 1 selftests: amd-pstate: amd-pstate-ut.sh
+
+    #. Results ::
+
+         $ dmesg | grep "amd_pstate_ut" | tee log.txt
+         [12977.570663] amd_pstate_ut: 1    amd_pstate_ut_acpi_cpc_valid  success!
+         [12977.570673] amd_pstate_ut: 2    amd_pstate_ut_check_enabled   success!
+         [12977.571207] amd_pstate_ut: 3    amd_pstate_ut_check_perf      success!
+         [12977.571212] amd_pstate_ut: 4    amd_pstate_ut_check_freq      success!
+
+Reference
+===========
+
+.. [1] AMD64 Architecture Programmer's Manual Volume 2: System Programming,
+       https://www.amd.com/system/files/TechDocs/24593.pdf
+
+.. [2] Advanced Configuration and Power Interface Specification,
+       https://uefi.org/sites/default/files/resources/ACPI_Spec_6_4_Jan22.pdf
+
+.. [3] Processor Programming Reference (PPR) for AMD Family 19h Model 51h, Revision A1 Processors
+       https://www.amd.com/system/files/TechDocs/56569-A1-PUB.zip
+
+.. [4] Linux Kernel Selftests,
+       https://www.kernel.org/doc/html/latest/dev-tools/kselftest.html