[Public]
Hi,
> -----Original Message-----
> From: Jan Beulich <jbeul...@suse.com>
> Sent: Monday, March 24, 2025 10:28 PM
> To: Penny, Zheng <penny.zh...@amd.com>
> Cc: Huang, Ray <ray.hu...@amd.com>; Andrew Cooper
> <andrew.coop...@citrix.com>; Roger Pau Monné <roger....@citrix.com>;
> Anthony PERARD <anthony.per...@vates.tech>; Orzel, Michal
> <michal.or...@amd.com>; Julien Grall <jul...@xen.org>; Stefano Stabellini
> <sstabell...@kernel.org>; xen-devel@lists.xenproject.org
> Subject: Re: [PATCH v3 02/15] xen/x86: introduce new sub-hypercall to
> propagate
> CPPC data
>
> On 06.03.2025 09:39, Penny Zheng wrote:
> > + pm_info = processor_pminfo[cpuid];
> > + /* Must already allocated in set_psd_pminfo */
> > + if ( !pm_info )
> > + {
> > + ret = -EINVAL;
> > + goto out;
> > + }
> > + pm_info->cppc_data = *cppc_data;
> > +
> > + if ( cpufreq_verbose )
> > + print_CPPC(&pm_info->cppc_data);
> > +
> > + pm_info->init = XEN_CPPC_INIT;
>
> That is - whichever Dom0 invoked last will have data recorded, and the other
> effectively is discarded? I think a warning (perhaps a one-time one) is
> minimally
> needed to diagnose the case where one type of data replaces the other.
>
In last v2 discussion, we are discussing that either set_px_pminfo or
set_cppc_pminfo shall be invoked,
which means either PX data is recorded, or CPPC data is recorded.
Current logic is that, cpufreq cmdline logic will set the
XEN_PROCESSOR_PM_PX/CPPC
flag to reflect user preference, if user defines the fallback option, like
"cpufreq=amd-cppc,xen", we will have both
XEN_PROCESSOR_PM_PX | XEN_PROCESSOR_PM_CPPC set in the beginning.
Later in cpufreq driver register logic, as only one register could be
registered , if amd-cppc
being registered successfully, it will clear the XEN_PROCESSOR_PM_PX flag bit.
But if it fails to register, fallback scheme kicks off, we will try the legacy
P-states, in the mean time,
clearing the XEN_PROCESSOR_PM_CPPC.
We are trying to make XEN_PROCESSOR_PM_PX and XEN_PROCESSOR_PM_CPPC exclusive
values after driver registration, which will ensure us that either
set_px_pminfo or set_cppc_pminfo
is taken in the runtime.
> With this it also remains unclear to me how fallback to the legacy driver is
> intended
> to be working. Both taken together are a strong suggestion that important
> information on the model that is being implemented is missing from the
> description.
>
> > @@ -27,8 +28,6 @@ struct processor_performance {
> > struct xen_pct_register status_register;
> > uint32_t state_count;
> > struct xen_processor_px *states;
> > -
> > - uint32_t init;
> > };
> >
> > struct processor_pminfo {
> > @@ -37,6 +36,9 @@ struct processor_pminfo {
> > struct xen_psd_package domain_info;
> > uint32_t shared_type;
> > struct processor_performance perf;
> > + struct xen_processor_cppc cppc_data;
> > +
> > + uint32_t init;
> > };
>
> This moving of the "init" field and the mechanical changes coming with it can
> likely
> be split out to a separate patch? Provided of course the movement is still
> wanted/needed with patch 1 re-worked or dropped.
>
> Jan
