[PATCH v2 00/21] cpufreq: introduce a new AMD CPU frequency control mechanism

From: Huang Rui
Date: Sun Sep 26 2021 - 05:06:49 EST

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Hi all,

We would like to introduce a new AMD CPU frequency control mechanism as the
"amd-pstate" driver for modern AMD Zen based CPU series in Linux Kernel.
The new mechanism is based on Collaborative processor performance control
(CPPC) which is finer grain frequency management than legacy ACPI hardware
P-States. Current AMD CPU platforms are using the ACPI P-states driver to
manage CPU frequency and clocks with switching only in 3 P-states. AMD
P-States is to replace 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. The first version for amd-pstate is to support one
of the Zen3 processors, and we will support more in future after we verify
the hardware and SBIOS functionalities.

There are two types of hardware implementations for amd-pstate: one is full
MSR support and another is shared memory support. It can use
X86_FEATURE_AMD_CPPC_EXT feature flag to distinguish the different types.

Using the new AMD P-States method + kernel governors (*schedutil*,
*ondemand*, ...) to manage the frequency update is the most appropriate
bridge between AMD Zen based hardware processor and Linux kernel, the
processor is able to ajust to the most efficiency frequency according to
the kernel scheduler loading.

Performance Per Watt (PPW) Caculation:

The PPW caculation is referred by below paper:
https://software.intel.com/content/dam/develop/external/us/en/documents/performance-per-what-paper.pdf

Below formula is referred from below spec to measure the PPW:

(F / t) / P = F * t / (t * E) = F / E,

"F" is the number of frames per second.
"P" is power measurd in watts.
"E" is energy measured in joules.

We use the RAPL interface with "perf" tool to get the energy data of the
package power.

The data comparsions between amd-pstate and acpi-freq module are tested on
AMD Cezanne processor:

1) TBench CPU benchmark:

+---------------------------------------------------------------------+
| |
| TBench (Performance Per Watt) |
| Higher is better |
+-------------------+------------------------+------------------------+
| | Performance Per Watt | Performance Per Watt |
| Kernel Module | (Schedutil) | (Ondemand) |
| | Unit: MB / (s * J) | Unit: MB / (s * J) |
+-------------------+------------------------+------------------------+
| | | |
| acpi-cpufreq | 3.022 | 2.969 |
| | | |
+-------------------+------------------------+------------------------+
| | | |
| amd-pstate | 3.131 | 3.284 |
| | | |
+-------------------+------------------------+------------------------+

2) Gitsource CPU benchmark:

+---------------------------------------------------------------------+
| |
| Gitsource (Performance Per Watt) |
| Higher is better |
+-------------------+------------------------+------------------------+
| | Performance Per Watt | Performance Per Watt |
| Kernel Module | (Schedutil) | (Ondemand) |
| | Unit: 1 / (s * J) | Unit: 1 / (s * J) |
+-------------------+------------------------+------------------------+
| | | |
| acpi-cpufreq | 3.42172E-07 | 2.74508E-07 |
| | | |
+-------------------+------------------------+------------------------+
| | | |
| amd-pstate | 4.09141E-07 | 3.47610E-07 |
| | | |
+-------------------+------------------------+------------------------+

3) Speedometer 2.0 CPU benchmark:

+---------------------------------------------------------------------+
| |
| Speedometer 2.0 (Performance Per Watt) |
| Higher is better |
+-------------------+------------------------+------------------------+
| | Performance Per Watt | Performance Per Watt |
| Kernel Module | (Schedutil) | (Ondemand) |
| | Unit: 1 / (s * J) | Unit: 1 / (s * J) |
+-------------------+------------------------+------------------------+
| | | |
| acpi-cpufreq | 0.116111767 | 0.110321664 |
| | | |
+-------------------+------------------------+------------------------+
| | | |
| amd-pstate | 0.115825281 | 0.122024299 |
| | | |
+-------------------+------------------------+------------------------+

According to above average data, we can see this solution has shown better
performance per watt scaling on mobile CPU benchmarks in most of cases.

These patch series depends on a "hotplug capable" CPU fix below (Only few
of CPU parts with "un-hotplug" core will encounter the issue and Mario is
working on the fix):
https://lore.kernel.org/linux-pm/20210813161842.222414-1-mario.limonciello@xxxxxxx/

And we can see patch series in below git repo:
V1: https://git.kernel.org/pub/scm/linux/kernel/git/rui/linux.git/log/?h=amd-pstate-dev-v1
V2: https://git.kernel.org/pub/scm/linux/kernel/git/rui/linux.git/log/?h=amd-pstate-dev-v2

For details introduction, please see the patch 19.

Changes from V1 -> V2:
- cpufreq:
- - Add detailed description in the commit log.
- - Clean up the "extension" postfix in the x86 feature flag.
- - Revise cppc_set_enable helper.
- - Add a fix to check online cpus in cppc_acpi.
- - Use static calls to avoid retpolines.
- - Revise the comment style.
- - Remove amd_pstate_boost_supported() function.
- - Revise the return value in syfs attribute functions.
- cpupower:
- - Refine the commit log for cpupower patches.
- - Expose a function to get the sysfs value from specific table.
- - Move amd-pstate sysfs definitions and functions into amd helper file.
- - Move the boost init function into amd helper file and explain the
details in the commit log.
- - Remove the amd_pstate_get_data in the lib/cpufreq.c to keep the lib as
common operations.
- - Move print_speed function into misc helper file.
- - Add amd_pstate_show_perf_and_freq() function in amd helper for
cpufreq-info print.

Thanks,
Ray

Huang Rui (19):
x86/cpufreatures: add AMD Collaborative Processor Performance Control
feature flag
x86/msr: add AMD CPPC MSR definitions
cpufreq: amd: introduce a new amd pstate driver to support future
processors
cpufreq: amd: add fast switch function for amd-pstate module
cpufreq: amd: add acpi cppc function as the backend for legacy
processors
cpufreq: amd: add trace for amd-pstate module
cpufreq: amd: add boost mode support for amd-pstate
cpufreq: amd: add amd-pstate checking support check attribute
cpufreq: amd: add amd-pstate frequencies attributes
cpufreq: amd: add amd-pstate performance attributes
cpupower: add AMD P-state capability flag
cpupower: add the function to check amd-pstate enabled
cpupower: initial AMD P-state capability
cpupower: add the function to get the sysfs value from specific table
cpupower: add amd-pstate sysfs definition and access helper
cpupower: enable boost state support for amd-pstate module
cpupower: move print_speed function into misc helper
cpupower: print amd-pstate information on cpupower
Documentation: amd-pstate: add amd-pstate driver introduction

Jinzhou Su (1):
ACPI: CPPC: add cppc enable register function

Mario Limonciello (1):
ACPI: CPPC: Check online CPUs for determining _CPC is valid

Documentation/admin-guide/pm/amd_pstate.rst | 377 +++++++++
.../admin-guide/pm/working-state.rst | 1 +
arch/x86/include/asm/cpufeatures.h | 1 +
arch/x86/include/asm/msr-index.h | 17 +
drivers/acpi/cppc_acpi.c | 50 +-
drivers/cpufreq/Kconfig.x86 | 13 +
drivers/cpufreq/Makefile | 5 +
drivers/cpufreq/amd-pstate-trace.c | 2 +
drivers/cpufreq/amd-pstate-trace.h | 96 +++
drivers/cpufreq/amd-pstate.c | 724 ++++++++++++++++++
include/acpi/cppc_acpi.h | 5 +
tools/power/cpupower/lib/cpufreq.c | 21 +-
tools/power/cpupower/lib/cpufreq.h | 12 +
tools/power/cpupower/utils/cpufreq-info.c | 68 +-
tools/power/cpupower/utils/helpers/amd.c | 82 ++
tools/power/cpupower/utils/helpers/cpuid.c | 13 +
tools/power/cpupower/utils/helpers/helpers.h | 21 +
tools/power/cpupower/utils/helpers/misc.c | 64 ++
18 files changed, 1514 insertions(+), 58 deletions(-)
create mode 100644 Documentation/admin-guide/pm/amd_pstate.rst
create mode 100644 drivers/cpufreq/amd-pstate-trace.c
create mode 100644 drivers/cpufreq/amd-pstate-trace.h
create mode 100644 drivers/cpufreq/amd-pstate.c

--
2.25.1

Next message: Huang Rui: "[PATCH v2 02/21] x86/msr: add AMD CPPC MSR definitions"
Previous message: Marc Zyngier: "Re: [PATCH 07/14] KVM: Don't block+unblock when halt-polling is successful"
Next in thread: Huang Rui: "[PATCH v2 02/21] x86/msr: add AMD CPPC MSR definitions"
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