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Wysocki" , Viresh Kumar , Shuah Khan , "Borislav Petkov" , Ingo Molnar , CC: Deepak Sharma , Alex Deucher , Mario Limonciello , Nathan Fontenot , Jinzhou Su , Xiaojian Du , , , Huang Rui Subject: [PATCH 19/19] Documentation: amd-pstate: add amd-pstate driver introduction Date: Wed, 8 Sep 2021 23:00:01 +0800 Message-ID: <20210908150001.3702552-20-ray.huang@amd.com> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20210908150001.3702552-1-ray.huang@amd.com> References: <20210908150001.3702552-1-ray.huang@amd.com> MIME-Version: 1.0 X-Originating-IP: [10.180.168.240] X-ClientProxiedBy: SATLEXMB04.amd.com (10.181.40.145) To SATLEXMB04.amd.com (10.181.40.145) X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-Office365-Filtering-Correlation-Id: 39f39b53-84bc-46d7-cb8c-08d972d99fd2 X-MS-TrafficTypeDiagnostic: DM6PR12MB4516: X-Microsoft-Antispam-PRVS: X-MS-Oob-TLC-OOBClassifiers: OLM:10000; X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0; X-Microsoft-Antispam-Message-Info: 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 X-Forefront-Antispam-Report: CIP:165.204.84.17; CTRY:US; LANG:en; SCL:1; SRV:; IPV:CAL; SFV:NSPM; H:SATLEXMB04.amd.com; PTR:InfoDomainNonexistent; CAT:NONE; SFS:(4636009)(346002)(39860400002)(376002)(136003)(396003)(46966006)(36840700001)(47076005)(30864003)(6666004)(5660300002)(7696005)(478600001)(186003)(16526019)(966005)(8936002)(110136005)(316002)(54906003)(82740400003)(8676002)(2906002)(336012)(36756003)(86362001)(2616005)(70586007)(70206006)(36860700001)(83380400001)(82310400003)(426003)(81166007)(26005)(356005)(4326008)(1076003)(36900700001); DIR:OUT; SFP:1101; X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 08 Sep 2021 15:02:06.2838 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 39f39b53-84bc-46d7-cb8c-08d972d99fd2 X-MS-Exchange-CrossTenant-Id: 3dd8961f-e488-4e60-8e11-a82d994e183d X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=3dd8961f-e488-4e60-8e11-a82d994e183d; Ip=[165.204.84.17]; Helo=[SATLEXMB04.amd.com] X-MS-Exchange-CrossTenant-AuthSource: CO1NAM11FT018.eop-nam11.prod.protection.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: DM6PR12MB4516 Precedence: bulk List-ID: X-Mailing-List: linux-pm@vger.kernel.org Introduce the amd-pstate driver design and implementation. Signed-off-by: Huang Rui --- Documentation/admin-guide/pm/amd_pstate.rst | 377 ++++++++++++++++++ .../admin-guide/pm/working-state.rst | 1 + 2 files changed, 378 insertions(+) create mode 100644 Documentation/admin-guide/pm/amd_pstate.rst diff --git a/Documentation/admin-guide/pm/amd_pstate.rst b/Documentation/admin-guide/pm/amd_pstate.rst new file mode 100644 index 000000000000..c3659dde0cee --- /dev/null +++ b/Documentation/admin-guide/pm/amd_pstate.rst @@ -0,0 +1,377 @@ +.. SPDX-License-Identifier: GPL-2.0 +.. include:: + +=============================================== +``amd-pstate`` CPU Performance Scaling Driver +=============================================== + +:Copyright: |copy| 2021 Advanced Micro Devices, Inc. + +:Author: Huang Rui + + +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, 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 +provides the low latency register model (MSR) instead of 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) +......................... + +It 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 be in +an idle state. This would be equivalent to the highest frequencies +supported by the processor. + +Nominal (Guaranteed) Performance (RO) +...................................... + +It is the maximum sustained performance level of the processor, assuming +ideal operating conditions. In 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) +................................... + +It 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) +........................ + +It 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, +processor must provide at least nominal performance requested and go higher +if current operating conditions allow. + +Energy Performance Preference (EPP) (RW) +......................................... + +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 adjust_perf callback to implement the CPPC similar performance +update behavior. It is initialized by ``sugov_start`` and then populate the +CPU's update_util_data pointer to assign ``sugov_update_single_perf`` as +the utilization update callback function in CPU scheduler. CPU scheduler +will call ``cpufreq_update_util`` and assign the target performance +according to the ``struct sugov_cpu`` that utilization update belongs to. +Then ``amd-pstate`` updates the desired performance according to the CPU +scheduler assigned. + + +Processor Support +======================= + +The ``amd-pstate`` initialization will fail if the _CPC in ACPI SBIOS is +not existed at the detected processor, and it uses ``acpi_cpc_valid`` to +check the _CPC existence. All Zen based processors support legacy ACPI +hardware P-States function, so while the ``amd-pstate`` fails to be +initialized, the kernel will fall back to initialize ``acpi-cpufreq`` +driver. + +There are two types of hardware implementations for ``amd-pstate``: one is +`Full MSR Support `_ and another is `Shared Memory Support +`_. It can use :c:macro:`X86_FEATURE_AMD_CPPC_EXT` feature flag +(for details refer to Processor Programming Reference (PPR) for AMD Family +19h Model 21h, Revision B0 Processors [3]_) to indicate the different +types. ``amd-pstate`` is to register different ``amd_pstate_perf_funcs`` +instances for different hardware implementations. + +Currently, some of 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_AMD_CPPC_EXT` CPU feature flag is set. +``amd-pstate`` can handle the MSR register to implement the fast switch +function in ``CPUFreq`` that can shrink latency of frequency control on the +interrupt context. + +Shared Memory Support +---------------------- + +If :c:macro:`X86_FEATURE_AMD_CPPC_EXT` CPU feature flag is not set, that +means the processor supports shared memory solution. In this case, +``amd-pstate`` uses the ``cppc_acpi`` helper methods to implement the +callback functions of ``amd_pstate_perf_funcs``. + + +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 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_lowest_nonlinear_perf + /sys/devices/system/cpu/cpufreq/policy0/amd_pstate_lowest_perf + /sys/devices/system/cpu/cpufreq/policy0/amd_pstate_max_freq + /sys/devices/system/cpu/cpufreq/policy0/amd_pstate_min_freq + /sys/devices/system/cpu/cpufreq/policy0/amd_pstate_nominal_freq + /sys/devices/system/cpu/cpufreq/policy0/amd_pstate_nominal_perf + /sys/devices/system/cpu/cpufreq/policy0/is_amd_pstate_enabled + + +``is_amd_pstate_enabled`` + +Query whether current kernel loads ``amd-pstate`` to enable the AMD +P-States functionality. +This attribute is read-only. + +``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 `_). +This attribute is read-only. + +``amd_pstate_nominal_perf / amd_pstate_nominal_freq`` + +Nominal CPPC performance and CPU frequency that the driver is allowed to +set in percent of the maximum supported CPPC performance level (Please see +nominal performance in `AMD CPPC Performance Capability `_). +This attribute is read-only. + +``amd_pstate_lowest_nonlinear_perf / amd_pstate_lowest_nonlinear_freq`` + +The lowest non-linear CPPC performance and 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 `_). +This attribute is read-only. + +``amd_pstate_lowest_perf / amd_pstate_min_freq`` + +The lowest physical CPPC performance and CPU frequency. +This attribute is read-only. + + +``amd-pstate`` vs ``acpi-cpufreq`` +====================================== + +On majority of AMD platforms supported by ``acpi-cpufreq``, the ACPI tables +provided by the platform firmware used for CPU performance scaling, but +only provides 3 P-states on AMD processors. +However, on modern AMD APU and CPU series, it provides the collaborative +processor performance control according to ACPI protocol and customize this +for AMD platforms. That is fine-grain and continuous frequency range +instead of the legacy hardware P-states. ``amd-pstate`` is the kernel +module which supports the new AMD P-States mechanism on most of future AMD +platforms. The AMD P-States mechanism will be the more performance and energy +efficiency frequency management method on AMD processors. + +``cpupower`` tool support for ``amd-pstate`` +=============================================== + +``amd-pstate`` is supported on ``cpupower`` tool that can be used to dump the frequency +information. And it is in progress to support more and more operations for 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 generally +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 + # | | | |||| | | + -0 [000] d.s. 244057.464842: amd_pstate_perf: amd_min_perf=39 amd_des_perf=39 amd_max_perf=166 cpu_id=0 prev=0x2727a6 value=0x2727a6 + -0 [000] d.h. 244057.475436: amd_pstate_perf: amd_min_perf=39 amd_des_perf=39 amd_max_perf=166 cpu_id=0 prev=0x2727a6 value=0x2727a6 + -0 [000] d.h. 244057.476629: amd_pstate_perf: amd_min_perf=39 amd_des_perf=39 amd_max_perf=166 cpu_id=0 prev=0x2727a6 value=0x2727a6 + -0 [000] d.s. 244057.484847: amd_pstate_perf: amd_min_perf=39 amd_des_perf=39 amd_max_perf=166 cpu_id=0 prev=0x2727a6 value=0x2727a6 + -0 [000] d.h. 244057.499821: amd_pstate_perf: amd_min_perf=39 amd_des_perf=39 amd_max_perf=166 cpu_id=0 prev=0x2727a6 value=0x2727a6 + avahi-daemon-528 [000] d... 244057.513568: amd_pstate_perf: amd_min_perf=39 amd_des_perf=39 amd_max_perf=166 cpu_id=0 prev=0x2727a6 value=0x2727a6 + +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). + + +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 21h, Revision B0 Processors + https://www.amd.com/system/files/TechDocs/55898_B1_pub_0.50.zip + diff --git a/Documentation/admin-guide/pm/working-state.rst b/Documentation/admin-guide/pm/working-state.rst index f40994c422dc..28db6156b55d 100644 --- a/Documentation/admin-guide/pm/working-state.rst +++ b/Documentation/admin-guide/pm/working-state.rst @@ -11,6 +11,7 @@ Working-State Power Management intel_idle cpufreq intel_pstate + amd_pstate cpufreq_drivers intel_epb intel-speed-select