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

["Penny, Zheng" <penny.zheng@xxxxxxx>]

[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);
```


> Jan