On 28.03.2025 09:27, Penny, Zheng wrote:
> [Public]
>
> Hi,
>
>> -----Original Message-----
>> From: Jan Beulich <jbeul...@suse.com>
>> Sent: Tuesday, March 25, 2025 3:54 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 25.03.2025 05:12, Penny, Zheng wrote:
>>>> -----Original Message-----
>>>> From: Jan Beulich <jbeul...@suse.com>
>>>> Sent: Monday, March 24, 2025 10:28 PM
>>>>
>>>> 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.
>>
>> Yet you realize that this implies Dom0 to know what configuration Xen uses,
>> in
>> order to know which data to upload. The best approach might be to have
>> Dom0 upload all data it has, with us merely ignoring what we can't make use
>> of.
>
> PLZ correct me if I understand you wrongly:
> Right now, I was letting DOM0 upload all data it has, and in the Xen:
> ```
> case XEN_PM_CPPC:
> if ( !(xen_processor_pmbits & XEN_PROCESSOR_PM_CPPC) )
> {
> ret = -EOPNOTSUPPED;
> break;
> }
> ret = set_cppc_pminfo(op->u.set_pminfo.id,
> &op->u.set_pminfo.u.cppc_data);
> break;
>
> case XEN_PM_PX:
> if ( !(xen_processor_pmbits & XEN_PROCESSOR_PM_PX) )
> {
> ret = -EOPNOTSUPPED;
> break;
> }
> ret = set_px_pminfo(op->u.set_pminfo.id, &op->u.set_pminfo.u.perf);
> break;
> ```
> I relied on flag XEN_PROCESSOR_PM_CPPC and XEN_PROCESSOR_PM_PX to choose which
> info we shall record.
> Firstly, we shall not return -EOPNOTSUPPED error above there.
Yes.
>> The order of uploading (CPPC first or CPPC last) shouldn't matter. Then (and
>> only
>> then, and - ftaod - only when uploading of the "wrong" kind of data doesn't
>> result in
>> an error) things can go without warning.
>
> Then in
> ```
> pm_info->init = XEN_CPPC_INIT;
> ret = cpufreq_cpu_init(cpuid);
> ```
> We shall add warning here to clarify no fallback scheme to replace now, when
> ret is not zero.
Maybe. In the earlier reply I said with certain conditions fulfilled a warning
may not be necessary. Yet perhaps initially having a warning there (maybe just
for debug builds) may make sense.
Jan
