Re: [PATCH v8 0/8] amd-cppc CPU Performance Scaling Driver

[Jan Beulich <jbeulich@xxxxxxxx>]

On 28.08.2025 12:02, Penny Zheng wrote:
> amd-cppc is the AMD CPU performance scaling driver that introduces a
> new CPU frequency control mechanism on modern AMD APU and CPU series in
> Xen. 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 Xen to directly
> communicate the performance hints to hardware.
> 
> amd_cppc driver has 2 operation modes: autonomous (active) mode,
> and non-autonomous (passive) mode. We register different CPUFreq driver
> for different modes, "amd-cppc" for passive mode and "amd-cppc-epp"
> for active mode.
> 
> The passive mode leverages common governors such as *ondemand*,
> *performance*, etc, to manage the performance tuning. While the active mode
> uses epp to provides a hint to the hardware if software wants to bias
> toward performance (0x0) or energy efficiency (0xff). CPPC power algorithm
> in hardware will automatically calculate the runtime workload and adjust the
> realtime cpu cores frequency according to the power supply and thermal, core
> voltage and some other hardware conditions.
> 
> amd-cppc is enabled on passive mode with a top-level `cpufreq=amd-cppc` 
> option,
> while users add extra `active` flag to select active mode.
> 
> With `cpufreq=amd-cppc,active`, we did a 60s sampling test to see the CPU
> frequency change, through tweaking the energy_perf preference from
> `xenpm set-cpufreq-cppc powersave` to `xenpm set-cpufreq-cppc performance`.
> The outputs are as follows:
> ```
> Setting CPU in powersave mode
> Sampling and Outputs:
>   Avg freq      580000 KHz
>   Avg freq      580000 KHz
>   Avg freq      580000 KHz
> Setting CPU in performance mode
> Sampling and Outputs:
>   Avg freq      4640000 KHz
>   Avg freq      4220000 KHz
>   Avg freq      4640000 KHz
> ```
> 
> Penny Zheng (8):
>   xen/cpufreq: introduce new sub-hypercall to propagate CPPC data
>   xen/cpufreq: introduce "cpufreq=amd-cppc" xen cmdline and amd-cppc
>     driver
>   xen/cpufreq: implement amd-cppc driver for CPPC in passive mode
>   xen/cpufreq: implement amd-cppc-epp driver for CPPC in active mode
>   xen/cpufreq: get performance policy from governor set via xenpm
>   tools/cpufreq: extract CPPC para from cpufreq para
>   xen/cpufreq: bypass governor-related para for amd-cppc-epp
>   xen/cpufreq: Adapt SET/GET_CPUFREQ_CPPC xen_sysctl_pm_op for amd-cppc
>     driver
> 
>  docs/misc/xen-command-line.pandoc         |  14 +-
>  tools/include/xenctrl.h                   |   3 +-
>  tools/libs/ctrl/xc_pm.c                   |  25 +-
>  tools/misc/xenpm.c                        |  94 ++-
>  xen/arch/x86/acpi/cpufreq/Makefile        |   1 +
>  xen/arch/x86/acpi/cpufreq/amd-cppc.c      | 766 ++++++++++++++++++++++
>  xen/arch/x86/acpi/cpufreq/cpufreq.c       |  69 +-
>  xen/arch/x86/cpu/amd.c                    |   8 +-
>  xen/arch/x86/include/asm/amd.h            |   2 +
>  xen/arch/x86/include/asm/msr-index.h      |   6 +
>  xen/arch/x86/platform_hypercall.c         |  19 +
>  xen/arch/x86/x86_64/cpufreq.c             |  19 +
>  xen/arch/x86/x86_64/platform_hypercall.c  |   3 +
>  xen/drivers/acpi/pm-op.c                  |  68 +-
>  xen/drivers/acpi/pmstat.c                 |   4 +
>  xen/drivers/cpufreq/cpufreq.c             | 137 +++-
>  xen/drivers/cpufreq/utility.c             |  15 +
>  xen/include/acpi/cpufreq/cpufreq.h        |  40 +-
>  xen/include/acpi/cpufreq/processor_perf.h |  14 +-
>  xen/include/public/platform.h             |  26 +
>  xen/include/public/sysctl.h               |   5 +-
>  xen/include/xen/pmstat.h                  |   5 +
>  xen/include/xlat.lst                      |   1 +
>  23 files changed, 1283 insertions(+), 61 deletions(-)
>  create mode 100644 xen/arch/x86/acpi/cpufreq/amd-cppc.c

Oh, and - what is still missing is a CHANGELOG.md entry.

Jan