1.. SPDX-License-Identifier: GPL-2.0 2.. include:: <isonum.txt> 3 4=============================================== 5``amd-pstate`` CPU Performance Scaling Driver 6=============================================== 7 8:Copyright: |copy| 2021 Advanced Micro Devices, Inc. 9 10:Author: Huang Rui <ray.huang@amd.com> 11 12 13Introduction 14=================== 15 16``amd-pstate`` is the AMD CPU performance scaling driver that introduces a 17new CPU frequency control mechanism on modern AMD APU and CPU series in 18Linux kernel. The new mechanism is based on Collaborative Processor 19Performance Control (CPPC) which provides finer grain frequency management 20than legacy ACPI hardware P-States. Current AMD CPU/APU platforms are using 21the ACPI P-states driver to manage CPU frequency and clocks with switching 22only in 3 P-states. CPPC replaces the ACPI P-states controls and allows a 23flexible, low-latency interface for the Linux kernel to directly 24communicate the performance hints to hardware. 25 26``amd-pstate`` leverages the Linux kernel governors such as ``schedutil``, 27``ondemand``, etc. to manage the performance hints which are provided by 28CPPC hardware functionality that internally follows the hardware 29specification (for details refer to AMD64 Architecture Programmer's Manual 30Volume 2: System Programming [1]_). Currently, ``amd-pstate`` supports basic 31frequency control function according to kernel governors on some of the 32Zen2 and Zen3 processors, and we will implement more AMD specific functions 33in future after we verify them on the hardware and SBIOS. 34 35 36AMD CPPC Overview 37======================= 38 39Collaborative Processor Performance Control (CPPC) interface enumerates a 40continuous, abstract, and unit-less performance value in a scale that is 41not tied to a specific performance state / frequency. This is an ACPI 42standard [2]_ which software can specify application performance goals and 43hints as a relative target to the infrastructure limits. AMD processors 44provide the low latency register model (MSR) instead of an AML code 45interpreter for performance adjustments. ``amd-pstate`` will initialize a 46``struct cpufreq_driver`` instance, ``amd_pstate_driver``, with the callbacks 47to manage each performance update behavior. :: 48 49 Highest Perf ------>+-----------------------+ +-----------------------+ 50 | | | | 51 | | | | 52 | | Max Perf ---->| | 53 | | | | 54 | | | | 55 Nominal Perf ------>+-----------------------+ +-----------------------+ 56 | | | | 57 | | | | 58 | | | | 59 | | | | 60 | | | | 61 | | | | 62 | | Desired Perf ---->| | 63 | | | | 64 | | | | 65 | | | | 66 | | | | 67 | | | | 68 | | | | 69 | | | | 70 | | | | 71 | | | | 72 Lowest non- | | | | 73 linear perf ------>+-----------------------+ +-----------------------+ 74 | | | | 75 | | Lowest perf ---->| | 76 | | | | 77 Lowest perf ------>+-----------------------+ +-----------------------+ 78 | | | | 79 | | | | 80 | | | | 81 0 ------>+-----------------------+ +-----------------------+ 82 83 AMD P-States Performance Scale 84 85 86.. _perf_cap: 87 88AMD CPPC Performance Capability 89-------------------------------- 90 91Highest Performance (RO) 92......................... 93 94This is the absolute maximum performance an individual processor may reach, 95assuming ideal conditions. This performance level may not be sustainable 96for long durations and may only be achievable if other platform components 97are in a specific state; for example, it may require other processors to be in 98an idle state. This would be equivalent to the highest frequencies 99supported by the processor. 100 101Nominal (Guaranteed) Performance (RO) 102...................................... 103 104This is the maximum sustained performance level of the processor, assuming 105ideal operating conditions. In the absence of an external constraint (power, 106thermal, etc.), this is the performance level the processor is expected to 107be able to maintain continuously. All cores/processors are expected to be 108able to sustain their nominal performance state simultaneously. 109 110Lowest non-linear Performance (RO) 111................................... 112 113This is the lowest performance level at which nonlinear power savings are 114achieved, for example, due to the combined effects of voltage and frequency 115scaling. Above this threshold, lower performance levels should be generally 116more energy efficient than higher performance levels. This register 117effectively conveys the most efficient performance level to ``amd-pstate``. 118 119Lowest Performance (RO) 120........................ 121 122This is the absolute lowest performance level of the processor. Selecting a 123performance level lower than the lowest nonlinear performance level may 124cause an efficiency penalty but should reduce the instantaneous power 125consumption of the processor. 126 127AMD CPPC Performance Control 128------------------------------ 129 130``amd-pstate`` passes performance goals through these registers. The 131register drives the behavior of the desired performance target. 132 133Minimum requested performance (RW) 134................................... 135 136``amd-pstate`` specifies the minimum allowed performance level. 137 138Maximum requested performance (RW) 139................................... 140 141``amd-pstate`` specifies a limit the maximum performance that is expected 142to be supplied by the hardware. 143 144Desired performance target (RW) 145................................... 146 147``amd-pstate`` specifies a desired target in the CPPC performance scale as 148a relative number. This can be expressed as percentage of nominal 149performance (infrastructure max). Below the nominal sustained performance 150level, desired performance expresses the average performance level of the 151processor subject to hardware. Above the nominal performance level, 152the processor must provide at least nominal performance requested and go higher 153if current operating conditions allow. 154 155Energy Performance Preference (EPP) (RW) 156......................................... 157 158This attribute provides a hint to the hardware if software wants to bias 159toward performance (0x0) or energy efficiency (0xff). 160 161 162Key Governors Support 163======================= 164 165``amd-pstate`` can be used with all the (generic) scaling governors listed 166by the ``scaling_available_governors`` policy attribute in ``sysfs``. Then, 167it is responsible for the configuration of policy objects corresponding to 168CPUs and provides the ``CPUFreq`` core (and the scaling governors attached 169to the policy objects) with accurate information on the maximum and minimum 170operating frequencies supported by the hardware. Users can check the 171``scaling_cur_freq`` information comes from the ``CPUFreq`` core. 172 173``amd-pstate`` mainly supports ``schedutil`` and ``ondemand`` for dynamic 174frequency control. It is to fine tune the processor configuration on 175``amd-pstate`` to the ``schedutil`` with CPU CFS scheduler. ``amd-pstate`` 176registers the adjust_perf callback to implement performance update behavior 177similar to CPPC. It is initialized by ``sugov_start`` and then populates the 178CPU's update_util_data pointer to assign ``sugov_update_single_perf`` as the 179utilization update callback function in the CPU scheduler. The CPU scheduler 180will call ``cpufreq_update_util`` and assigns the target performance according 181to the ``struct sugov_cpu`` that the utilization update belongs to. 182Then, ``amd-pstate`` updates the desired performance according to the CPU 183scheduler assigned. 184 185.. _processor_support: 186 187Processor Support 188======================= 189 190The ``amd-pstate`` initialization will fail if the ``_CPC`` entry in the ACPI 191SBIOS does not exist in the detected processor. It uses ``acpi_cpc_valid`` 192to check the existence of ``_CPC``. All Zen based processors support the legacy 193ACPI hardware P-States function, so when ``amd-pstate`` fails initialization, 194the kernel will fall back to initialize the ``acpi-cpufreq`` driver. 195 196There are two types of hardware implementations for ``amd-pstate``: one is 197`Full MSR Support <perf_cap_>`_ and another is `Shared Memory Support 198<perf_cap_>`_. It can use the :c:macro:`X86_FEATURE_CPPC` feature flag to 199indicate the different types. (For details, refer to the Processor Programming 200Reference (PPR) for AMD Family 19h Model 51h, Revision A1 Processors [3]_.) 201``amd-pstate`` is to register different ``static_call`` instances for different 202hardware implementations. 203 204Currently, some of the Zen2 and Zen3 processors support ``amd-pstate``. In the 205future, it will be supported on more and more AMD processors. 206 207Full MSR Support 208----------------- 209 210Some new Zen3 processors such as Cezanne provide the MSR registers directly 211while the :c:macro:`X86_FEATURE_CPPC` CPU feature flag is set. 212``amd-pstate`` can handle the MSR register to implement the fast switch 213function in ``CPUFreq`` that can reduce the latency of frequency control in 214interrupt context. The functions with a ``pstate_xxx`` prefix represent the 215operations on MSR registers. 216 217Shared Memory Support 218---------------------- 219 220If the :c:macro:`X86_FEATURE_CPPC` CPU feature flag is not set, the 221processor supports the shared memory solution. In this case, ``amd-pstate`` 222uses the ``cppc_acpi`` helper methods to implement the callback functions 223that are defined on ``static_call``. The functions with the ``cppc_xxx`` prefix 224represent the operations of ACPI CPPC helpers for the shared memory solution. 225 226 227AMD P-States and ACPI hardware P-States always can be supported in one 228processor. But AMD P-States has the higher priority and if it is enabled 229with :c:macro:`MSR_AMD_CPPC_ENABLE` or ``cppc_set_enable``, it will respond 230to the request from AMD P-States. 231 232 233User Space Interface in ``sysfs`` 234================================== 235 236``amd-pstate`` exposes several global attributes (files) in ``sysfs`` to 237control its functionality at the system level. They are located in the 238``/sys/devices/system/cpu/cpufreq/policyX/`` directory and affect all CPUs. :: 239 240 root@hr-test1:/home/ray# ls /sys/devices/system/cpu/cpufreq/policy0/*amd* 241 /sys/devices/system/cpu/cpufreq/policy0/amd_pstate_highest_perf 242 /sys/devices/system/cpu/cpufreq/policy0/amd_pstate_lowest_nonlinear_freq 243 /sys/devices/system/cpu/cpufreq/policy0/amd_pstate_max_freq 244 245 246``amd_pstate_highest_perf / amd_pstate_max_freq`` 247 248Maximum CPPC performance and CPU frequency that the driver is allowed to 249set, in percent of the maximum supported CPPC performance level (the highest 250performance supported in `AMD CPPC Performance Capability <perf_cap_>`_). 251In some ASICs, the highest CPPC performance is not the one in the ``_CPC`` 252table, so we need to expose it to sysfs. If boost is not active, but 253still supported, this maximum frequency will be larger than the one in 254``cpuinfo``. 255This attribute is read-only. 256 257``amd_pstate_lowest_nonlinear_freq`` 258 259The lowest non-linear CPPC CPU frequency that the driver is allowed to set, 260in percent of the maximum supported CPPC performance level. (Please see the 261lowest non-linear performance in `AMD CPPC Performance Capability 262<perf_cap_>`_.) 263This attribute is read-only. 264 265Other performance and frequency values can be read back from 266``/sys/devices/system/cpu/cpuX/acpi_cppc/``, see :ref:`cppc_sysfs`. 267 268 269``amd-pstate`` vs ``acpi-cpufreq`` 270====================================== 271 272On the majority of AMD platforms supported by ``acpi-cpufreq``, the ACPI tables 273provided by the platform firmware are used for CPU performance scaling, but 274only provide 3 P-states on AMD processors. 275However, on modern AMD APU and CPU series, hardware provides the Collaborative 276Processor Performance Control according to the ACPI protocol and customizes this 277for AMD platforms. That is, fine-grained and continuous frequency ranges 278instead of the legacy hardware P-states. ``amd-pstate`` is the kernel 279module which supports the new AMD P-States mechanism on most of the future AMD 280platforms. The AMD P-States mechanism is the more performance and energy 281efficiency frequency management method on AMD processors. 282 283Kernel Module Options for ``amd-pstate`` 284========================================= 285 286.. _shared_mem: 287 288``shared_mem`` 289Use a module param (shared_mem) to enable related processors manually with 290**amd_pstate.shared_mem=1**. 291Due to the performance issue on the processors with `Shared Memory Support 292<perf_cap_>`_, we disable it presently and will re-enable this by default 293once we address performance issue with this solution. 294 295To check whether the current processor is using `Full MSR Support <perf_cap_>`_ 296or `Shared Memory Support <perf_cap_>`_ : :: 297 298 ray@hr-test1:~$ lscpu | grep cppc 299 Flags: fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush mmx fxsr sse sse2 ht syscall nx mmxext fxsr_opt pdpe1gb rdtscp lm constant_tsc rep_good nopl nonstop_tsc cpuid extd_apicid aperfmperf rapl pni pclmulqdq monitor ssse3 fma cx16 sse4_1 sse4_2 x2apic movbe popcnt aes xsave avx f16c rdrand lahf_lm cmp_legacy svm extapic cr8_legacy abm sse4a misalignsse 3dnowprefetch osvw ibs skinit wdt tce topoext perfctr_core perfctr_nb bpext perfctr_llc mwaitx cpb cat_l3 cdp_l3 hw_pstate ssbd mba ibrs ibpb stibp vmmcall fsgsbase bmi1 avx2 smep bmi2 erms invpcid cqm rdt_a rdseed adx smap clflushopt clwb sha_ni xsaveopt xsavec xgetbv1 xsaves cqm_llc cqm_occup_llc cqm_mbm_total cqm_mbm_local clzero irperf xsaveerptr rdpru wbnoinvd cppc arat npt lbrv svm_lock nrip_save tsc_scale vmcb_clean flushbyasid decodeassists pausefilter pfthreshold avic v_vmsave_vmload vgif v_spec_ctrl umip pku ospke vaes vpclmulqdq rdpid overflow_recov succor smca fsrm 300 301If the CPU flags have ``cppc``, then this processor supports `Full MSR Support 302<perf_cap_>`_. Otherwise, it supports `Shared Memory Support <perf_cap_>`_. 303 304 305``cpupower`` tool support for ``amd-pstate`` 306=============================================== 307 308``amd-pstate`` is supported by the ``cpupower`` tool, which can be used to dump 309frequency information. Development is in progress to support more and more 310operations for the new ``amd-pstate`` module with this tool. :: 311 312 root@hr-test1:/home/ray# cpupower frequency-info 313 analyzing CPU 0: 314 driver: amd-pstate 315 CPUs which run at the same hardware frequency: 0 316 CPUs which need to have their frequency coordinated by software: 0 317 maximum transition latency: 131 us 318 hardware limits: 400 MHz - 4.68 GHz 319 available cpufreq governors: ondemand conservative powersave userspace performance schedutil 320 current policy: frequency should be within 400 MHz and 4.68 GHz. 321 The governor "schedutil" may decide which speed to use 322 within this range. 323 current CPU frequency: Unable to call hardware 324 current CPU frequency: 4.02 GHz (asserted by call to kernel) 325 boost state support: 326 Supported: yes 327 Active: yes 328 AMD PSTATE Highest Performance: 166. Maximum Frequency: 4.68 GHz. 329 AMD PSTATE Nominal Performance: 117. Nominal Frequency: 3.30 GHz. 330 AMD PSTATE Lowest Non-linear Performance: 39. Lowest Non-linear Frequency: 1.10 GHz. 331 AMD PSTATE Lowest Performance: 15. Lowest Frequency: 400 MHz. 332 333 334Diagnostics and Tuning 335======================= 336 337Trace Events 338-------------- 339 340There are two static trace events that can be used for ``amd-pstate`` 341diagnostics. One of them is the ``cpu_frequency`` trace event generally used 342by ``CPUFreq``, and the other one is the ``amd_pstate_perf`` trace event 343specific to ``amd-pstate``. The following sequence of shell commands can 344be used to enable them and see their output (if the kernel is 345configured to support event tracing). :: 346 347 root@hr-test1:/home/ray# cd /sys/kernel/tracing/ 348 root@hr-test1:/sys/kernel/tracing# echo 1 > events/amd_cpu/enable 349 root@hr-test1:/sys/kernel/tracing# cat trace 350 # tracer: nop 351 # 352 # entries-in-buffer/entries-written: 47827/42233061 #P:2 353 # 354 # _-----=> irqs-off 355 # / _----=> need-resched 356 # | / _---=> hardirq/softirq 357 # || / _--=> preempt-depth 358 # ||| / delay 359 # TASK-PID CPU# |||| TIMESTAMP FUNCTION 360 # | | | |||| | | 361 <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 362 <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 363 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 364 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 365 <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 366 <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 367 <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 368 369The ``cpu_frequency`` trace event will be triggered either by the ``schedutil`` scaling 370governor (for the policies it is attached to), or by the ``CPUFreq`` core (for the 371policies with other scaling governors). 372 373 374Tracer Tool 375------------- 376 377``amd_pstate_tracer.py`` can record and parse ``amd-pstate`` trace log, then 378generate performance plots. This utility can be used to debug and tune the 379performance of ``amd-pstate`` driver. The tracer tool needs to import intel 380pstate tracer. 381 382Tracer tool located in ``linux/tools/power/x86/amd_pstate_tracer``. It can be 383used in two ways. If trace file is available, then directly parse the file 384with command :: 385 386 ./amd_pstate_trace.py [-c cpus] -t <trace_file> -n <test_name> 387 388Or generate trace file with root privilege, then parse and plot with command :: 389 390 sudo ./amd_pstate_trace.py [-c cpus] -n <test_name> -i <interval> [-m kbytes] 391 392The test result can be found in ``results/test_name``. Following is the example 393about part of the output. :: 394 395 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 396 CPU_005 712 116384 39 49 166 0.7565 9645075 2214891 38431470 25.1 11.646 469 2.496 kworker/5:0-40 397 CPU_006 712 116408 39 49 166 0.6769 8950227 1839034 37192089 24.06 11.272 470 2.496 kworker/6:0-1264 398 399Unit Tests for amd-pstate 400------------------------- 401 402``amd-pstate-ut`` is a test module for testing the ``amd-pstate`` driver. 403 404 * It can help all users to verify their processor support (SBIOS/Firmware or Hardware). 405 406 * Kernel can have a basic function test to avoid the kernel regression during the update. 407 408 * We can introduce more functional or performance tests to align the result together, it will benefit power and performance scale optimization. 409 4101. Test case decriptions 411 412 +---------+--------------------------------+------------------------------------------------------------------------------------+ 413 | Index | Functions | Description | 414 +=========+================================+====================================================================================+ 415 | 0 | amd_pstate_ut_acpi_cpc_valid || Check whether the _CPC object is present in SBIOS. | 416 | | || | 417 | | || The detail refer to `Processor Support <processor_support_>`_. | 418 +---------+--------------------------------+------------------------------------------------------------------------------------+ 419 | 1 | amd_pstate_ut_check_enabled || Check whether AMD P-State is enabled. | 420 | | || | 421 | | || AMD P-States and ACPI hardware P-States always can be supported in one processor. | 422 | | | But AMD P-States has the higher priority and if it is enabled with | 423 | | | :c:macro:`MSR_AMD_CPPC_ENABLE` or ``cppc_set_enable``, it will respond to the | 424 | | | request from AMD P-States. | 425 +---------+--------------------------------+------------------------------------------------------------------------------------+ 426 | 2 | amd_pstate_ut_check_perf || Check if the each performance values are reasonable. | 427 | | || highest_perf >= nominal_perf > lowest_nonlinear_perf > lowest_perf > 0. | 428 +---------+--------------------------------+------------------------------------------------------------------------------------+ 429 | 3 | amd_pstate_ut_check_freq || Check if the each frequency values and max freq when set support boost mode | 430 | | | are reasonable. | 431 | | || max_freq >= nominal_freq > lowest_nonlinear_freq > min_freq > 0 | 432 | | || If boost is not active but supported, this maximum frequency will be larger than | 433 | | | the one in ``cpuinfo``. | 434 +---------+--------------------------------+------------------------------------------------------------------------------------+ 435 436#. How to execute the tests 437 438 We use test module in the kselftest frameworks to implement it. 439 We create amd-pstate-ut module and tie it into kselftest.(for 440 details refer to Linux Kernel Selftests [4]_). 441 442 1. Build 443 444 + open the :c:macro:`CONFIG_X86_AMD_PSTATE` configuration option. 445 + set the :c:macro:`CONFIG_X86_AMD_PSTATE_UT` configuration option to M. 446 + make project 447 + make selftest :: 448 449 $ cd linux 450 $ make -C tools/testing/selftests 451 452 #. Installation & Steps :: 453 454 $ make -C tools/testing/selftests install INSTALL_PATH=~/kselftest 455 $ sudo ./kselftest/run_kselftest.sh -c amd-pstate 456 TAP version 13 457 1..1 458 # selftests: amd-pstate: amd-pstate-ut.sh 459 # amd-pstate-ut: ok 460 ok 1 selftests: amd-pstate: amd-pstate-ut.sh 461 462 #. Results :: 463 464 $ dmesg | grep "amd_pstate_ut" | tee log.txt 465 [12977.570663] amd_pstate_ut: 1 amd_pstate_ut_acpi_cpc_valid success! 466 [12977.570673] amd_pstate_ut: 2 amd_pstate_ut_check_enabled success! 467 [12977.571207] amd_pstate_ut: 3 amd_pstate_ut_check_perf success! 468 [12977.571212] amd_pstate_ut: 4 amd_pstate_ut_check_freq success! 469 470Reference 471=========== 472 473.. [1] AMD64 Architecture Programmer's Manual Volume 2: System Programming, 474 https://www.amd.com/system/files/TechDocs/24593.pdf 475 476.. [2] Advanced Configuration and Power Interface Specification, 477 https://uefi.org/sites/default/files/resources/ACPI_Spec_6_4_Jan22.pdf 478 479.. [3] Processor Programming Reference (PPR) for AMD Family 19h Model 51h, Revision A1 Processors 480 https://www.amd.com/system/files/TechDocs/56569-A1-PUB.zip 481 482.. [4] Linux Kernel Selftests, 483 https://www.kernel.org/doc/html/latest/dev-tools/kselftest.html 484