Re: [PATCH v1 00/11] amd-pstate CPU Performance Scaling Driver

[Jan Beulich <jbeulich@xxxxxxxx>]

On 03.12.2024 09:11, Penny Zheng wrote:
> 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
> 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_pstate CPPC has 2 operation modes: autonomous (active) mode,
> and non-autonomous (passive) mode. We register different CPUFreq driver
> for different modes, "amd-pstate" for passive mode and "amd-pstate-epp"
> for active mode.
> 
> The passive mode leverages common governors such as *ondemand*,
> *performance*, etc, to manage the performance hints. And 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
> will 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-pstate is enabled with a top-level cpufreq=amd-pstate option. It will
> fallback to cpufreq=xen if amd-pstate is unavailable.
> 
> With `cpufreq=amd-pstate,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      2000000 KHz
>   Avg freq      2000000 KHz
>   Avg freq      2000000 KHz
> Setting CPU in performance mode
> Sampling and Outputs:
>   Avg freq      4640000 KHz
>   Avg freq      4220000 KHz
>   Avg freq      4640000 KHz
> ```
> 
> Penny Zheng (11):
>   xen/x86: add CPPC feature flag for AMD processors
>   xen/x86: introduce new sub-hypercall to get CPPC data
>   xen/x86: introduce "cpufreq=amd-pstate" xen cmdline
>   xen/x86: get processor max speed from DMI table
>   xen/x86: introduce a new amd pstate driver for cpufreq scaling
>   xen/cpufreq: introduce policy type when cpufreq_driver->setpolicy
>     exists
>   xen/cpufreq: only set gov NULL when cpufreq_driver.target() exists
>   x86/cpufreq: add "cpufreq=amd-pstate,active" para
>   xen/x86: implement EPP support for the AMD processors
>   tools/xenpm: Print CPPC parameters for amd-pstate driver
>   xen/cpufreq: Adapt SET/GET_CPUFREQ_CPPC xen_sysctl_pm_op for
>     amd-pstate driver

Just to clarify: While certainly fine, it is a little surprising to see
such a submission just after the submission deadline for 4.20 was passed.
This is intended for 4.21 then, I expect? Or else have you talked to the
release manager?

Jan