Re: [PATCH v7 13/13] xen/cpufreq: Adapt SET/GET_CPUFREQ_CPPC xen_sysctl_pm_op for amd-cppc driver

[Jan Beulich <jbeulich@xxxxxxxx>]

On 28.08.2025 08:54, Penny, Zheng wrote:
> [Public]
> 
>> -----Original Message-----
>> From: Jan Beulich <jbeulich@xxxxxxxx>
>> Sent: Thursday, August 28, 2025 2:38 PM
>> To: Penny, Zheng <penny.zheng@xxxxxxx>
>> Cc: Huang, Ray <Ray.Huang@xxxxxxx>; Anthony PERARD
>> <anthony.perard@xxxxxxxxxx>; Andrew Cooper <andrew.cooper3@xxxxxxxxxx>;
>> Orzel, Michal <Michal.Orzel@xxxxxxx>; Julien Grall <julien@xxxxxxx>; Roger 
>> Pau
>> Monné <roger.pau@xxxxxxxxxx>; Stefano Stabellini <sstabellini@xxxxxxxxxx>; 
>> xen-
>> devel@xxxxxxxxxxxxxxxxxxxx
>> Subject: Re: [PATCH v7 13/13] xen/cpufreq: Adapt SET/GET_CPUFREQ_CPPC
>> xen_sysctl_pm_op for amd-cppc driver
>>
>> On 28.08.2025 08:35, Jan Beulich wrote:
>>> On 28.08.2025 06:06, Penny, Zheng wrote:
>>>>> -----Original Message-----
>>>>> From: Jan Beulich <jbeulich@xxxxxxxx>
>>>>> Sent: Tuesday, August 26, 2025 12:03 AM
>>>>>
>>>>> On 22.08.2025 12:52, Penny Zheng wrote:
>>>>>> --- a/xen/include/public/sysctl.h
>>>>>> +++ b/xen/include/public/sysctl.h
>>>>>> @@ -336,8 +336,14 @@ struct xen_ondemand {
>>>>>>      uint32_t up_threshold;
>>>>>>  };
>>>>>>
>>>>>> +#define CPUFREQ_POLICY_UNKNOWN      0
>>>>>> +#define CPUFREQ_POLICY_POWERSAVE    1
>>>>>> +#define CPUFREQ_POLICY_PERFORMANCE  2
>>>>>> +#define CPUFREQ_POLICY_ONDEMAND     3
>>>>>
>>>>> Without XEN_ prefixes they shouldn't appear in a public header. But
>>>>> do we need ...
>>>>>
>>>>>>  struct xen_get_cppc_para {
>>>>>>      /* OUT */
>>>>>> +    uint32_t policy; /* CPUFREQ_POLICY_xxx */
>>>>>
>>>>> ... the new field at all? Can't you synthesize the kind-of-governor
>>>>> into struct xen_get_cpufreq_para's respective field? You invoke both
>>>>> sub-ops from xenpm now anyway ...
>>>>>
>>>>
>>>> Maybe I could borrow governor field to indicate policy info, like the 
>>>> following in
>> print_cpufreq_para(), then we don't need to add the new filed "policy"
>>>> ```
>>>> +    /* Translate governor info to policy info in CPPC active mode */
>>>> +    if ( is_cppc_active )
>>>> +    {
>>>> +        if ( !strncmp(p_cpufreq->u.s.scaling_governor,
>>>> +                      "ondemand", CPUFREQ_NAME_LEN) )
>>>> +            printf("cppc policy           : ondemand\n");
>>>> +        else if ( !strncmp(p_cpufreq->u.s.scaling_governor,
>>>> +                           "performance", CPUFREQ_NAME_LEN) )
>>>> +            printf("cppc policy           : performance\n");
>>>> +
>>>> +        else if ( !strncmp(p_cpufreq->u.s.scaling_governor,
>>>> +                           "powersave", CPUFREQ_NAME_LEN) )
>>>> +            printf("cppc policy           : powersave\n");
>>>> +        else
>>>> +            printf("cppc policy           : unknown\n");
>>>> +    }
>>>> +
>>>> ```
>>>
>>> Something like this is what I was thinking of, yes.
>>
>> Albeit - why the complicated if/else sequence? Why not simply print the 
>> field the
>> hypercall returned?
> 
> userspace governor doesn't have according policy. I could simplify it to
> ```
>         if ( !strncmp(p_cpufreq->u.s.scaling_governor,
>              "userspace", CPUFREQ_NAME_LEN) )
>                 printf("policy               : unknown\n");
>         else
>                 printf("policy               : %s\n",
>                           p_cpufreq->u.s.scaling_governor);
> ```

But the hypervisor shouldn't report back "userspace" when the CPPC driver
is in use. ANd I think the tool is okay to trust the hypervisor.

Jan