Re: [PATCH v4 12/15] tools/xenpm: Print CPPC parameters for amd-cppc driver

[Jan Beulich <jbeulich@xxxxxxxx>]

On 20.05.2025 10:22, Penny, Zheng wrote:
>> -----Original Message-----
>> From: Jan Beulich <jbeulich@xxxxxxxx>
>> Sent: Tuesday, May 13, 2025 4:03 PM
>>
>> On 09.05.2025 08:36, Penny, Zheng wrote:
>>>> -----Original Message-----
>>>> From: Jan Beulich <jbeulich@xxxxxxxx>
>>>> Sent: Wednesday, April 30, 2025 9:55 PM
>>>>
>>>> On 14.04.2025 09:40, Penny Zheng wrote:
>>>>> HWP, amd-cppc, amd-cppc-epp are all the implementation of ACPI CPPC
>>>>> (Collaborative Processor Performace Control), so we introduce
>>>>> cppc_mode flag to print CPPC-related para.
>>>>>
>>>>> And HWP and amd-cppc-epp are both governor-less driver, so we
>>>>> introduce hw_auto flag to bypass governor-related print.
>>>>
>>>> But in the EPP driver you use the information which governor is active.
>>>
>>> We want to have a one-one mapping between governor and epp value, such
>>> as, If users choose performance governor, no matter via "xenpm" or
>>> cmdline, users want maximum performance, We set epp with 0 to meet the
>> expectation.
>>> And if users choose powersave governor, users want the least power
>>> consumption, then we shall set epp with 255 to meet the expectation.
>>
>> That's all fine, but completely misses the point of my question: If the 
>> governor is
>> relevant, why would you bypass respective printing?
>>
> 
> The only useful info in governor for epp mode, IMO, is its name.
> I deduce which performance policy user wants to apply through which governor 
> they choose.
> If user chooses performance governor, they want maximum performance.
> If user chooses powersave governor, they want the least power consumption
> I could only provide appropriate epp value in above two scenarios.
> ondemand and userspace are forbidden choices, and if users specify such 
> options in cmdline,
> I shall give warning message to say  that amd-cppc in active mode is 
> governor-less, and users could
> set epp values on runtime to specify bias towards performance or efficiency.
> 
> If above is messy, I could also totally forbid governor thing for active 
> mode... wdyt?

Then how would one pick between performance and powersave?

Jan