Re: [PATCH v2 07/11] x86/cpufreq: add "cpufreq=amd-cppc,active" para

[Jan Beulich <jbeulich@xxxxxxxx>]

On 06.02.2025 09:32, Penny Zheng wrote:
> --- a/docs/misc/xen-command-line.pandoc
> +++ b/docs/misc/xen-command-line.pandoc
> @@ -515,7 +515,7 @@ If set, force use of the performance counters for 
> oprofile, rather than detectin
>  available support.
>  
>  ### cpufreq
> -> `= none | {{ <boolean> | xen } { 
> [:[powersave|performance|ondemand|userspace][,[<maxfreq>]][,[<minfreq>]]] } 
> [,verbose]} | dom0-kernel | hwp[:[<hdc>][,verbose]] | amd-cppc[:[verbose]]`
> +> `= none | {{ <boolean> | xen } { 
> [:[powersave|performance|ondemand|userspace][,[<maxfreq>]][,[<minfreq>]]] } 
> [,verbose]} | dom0-kernel | hwp[:[<hdc>][,verbose]] | 
> amd-cppc[:[active][,verbose]]`
>  
>  > Default: `xen`
>  
> @@ -538,6 +538,12 @@ choice of `dom0-kernel` is deprecated and not supported 
> by all Dom0 kernels.
>    on supported AMD hardware to provide finer grained frequency control 
> mechanism.
>    The default is disabled. If `amd-cppc` is selected, but hardware support
>    is not available, Xen will fallback to cpufreq=xen.
> +* `active` is a boolean to enable amd-cppc driver in active(autonomous) mode.
> +  In this mode, users could provide a hint with energy performance preference
> +  register to the hardware if they want to bias toward performance(0x0) or
> +  energy efficiency(0xff), then CPPC power algorithm will calculate the 
> runtime
> +  workload and adjust the realtime cores frequency according to the power 
> supply
> +  and thermal, core voltage and some other hardware conditions.

All the option offers to the user is a boolean. The description wants to be
written based on that; to be honest, with what is there and with the new
variable not actually consumed anywhere, I have no real idea what this is
about. Hex numbers in particular don't belong here at all, imo. And "users
could provide a hint" needs to be more practical: Users don't directly write
to the "energy performance preference register" (or any other one).

> --- a/xen/arch/x86/acpi/cpufreq/amd-cppc.c
> +++ b/xen/arch/x86/acpi/cpufreq/amd-cppc.c
> @@ -33,6 +33,8 @@
>  #define amd_cppc_warn(fmt, args...)                         \
>      printk(XENLOG_WARNING "AMD_CPPC: CPU%u warning: " fmt, cpu, ## args)
>  
> +static bool __ro_after_init opt_cpufreq_active;

The name is ambiguous. It reads as if this was a global enable/disable for
the cpufreq subsystem. opt_active_mode perhaps, seeing this is local to
the CPPC driver?

Jan