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

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

[Public]

> -----Original Message-----
> From: Jan Beulich <jbeulich@xxxxxxxx>
> Sent: Tuesday, May 20, 2025 5:18 PM
> To: Penny, Zheng <penny.zheng@xxxxxxx>
> Cc: Huang, Ray <Ray.Huang@xxxxxxx>; Anthony PERARD
> <anthony.perard@xxxxxxxxxx>; xen-devel@xxxxxxxxxxxxxxxxxxxx
> Subject: Re: [PATCH v4 12/15] tools/xenpm: Print CPPC parameters for amd-cppc
> driver
>
> 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?

In hwp, we defined
"
#define CPPC_ENERGY_PERF_BALANCE         0x80
"
to provide the balanced value. Users could run "xenpm set-cpufreq-cppc balance" 
to achieve on runtime
Any other specific epp value, users shall run "xenpm set-cpufreq-cppc 
energy-perf:N" to achieve
We didn't provide any options in cmdline, so I tried to re-use the governor to 
achieve a few. hmmm,
now it seems it brings confusion....

>
> Jan