Re: [PATCH v5 00/18] amd-cppc CPU Performance Scaling Driver

[Jan Beulich <jbeulich@xxxxxxxx>]

On 27.05.2025 10:48, 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 (18):
>   xen/cpufreq: guard perf.states[] access with XEN_PX_INIT
>   xen/cpufreq: move "init" flag into common structure
>   xen/cpufreq: extract _PSD info from "struct xen_processor_performance"
>   xen/cpufreq: introduce new sub-hypercall to propagate CPPC data
>   xen/cpufreq: refactor cmdline "cpufreq=xxx"
>   xen/cpufreq: introduce "cpufreq=amd-cppc" xen cmdline
>   xen/cpufreq: disable px statistic info in amd-cppc mode
>   xen/cpu: Expand core frequency calculation for AMD Family 1Ah CPUs
>   xen/amd: introduce amd_process_freq() to get processor frequency
>   xen/cpufreq: introduce a new amd cppc driver for cpufreq scaling
>   xen/cpufreq: implement EPP support for the amd-cppc driver in active
>     mode
>   xen/cpufreq: get performance policy from governor set via xenpm
>   xen/cpufreq: normalize hwp driver check with hwp_active()
>   xen/cpufreq: introduce GET_CPUFREQ_CPPC sub-cmd
>   xen/cpufreq: bypass governor-related para for amd-cppc-epp
>   tools: drop "has_num" condition check for cppc mode
>   tools: optimize cpufreq average freq print
>   xen/cpufreq: Adapt SET/GET_CPUFREQ_CPPC xen_sysctl_pm_op for amd-cppc
>     driver

As indicated in individual replies, three of the patches may be possible to
go in before you re-post. Subject to what I said in the replies (patches 02,
08, and 13). Please clarify what (if anything) to do.

Jan