linux-kernel - Re: [PATCH v1 1/4] xen/acpi: upload power and performance related data from a PVH dom0

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Message-ID: <89ab9108-aa40-4da4-8e9f-dfa3bd49e2f4@amd.com>
Date: Wed, 4 Dec 2024 14:11:52 -0500
From: Jason Andryuk <jason.andryuk@....com>
To: Jürgen Groß <jgross@...e.com>, Penny Zheng
	<Penny.Zheng@....com>, Stefano Stabellini <sstabellini@...nel.org>, Oleksandr
 Tyshchenko <oleksandr_tyshchenko@...m.com>
CC: Ray Huang <Ray.Huang@....com>, Xenia Ragiadakou
	<Xenia.Ragiadakou@....com>, <xen-devel@...ts.xenproject.org>,
	<linux-kernel@...r.kernel.org>, Roger Pau Monné
	<roger.pau@...rix.com>
Subject: Re: [PATCH v1 1/4] xen/acpi: upload power and performance related
 data from a PVH dom0

On 2024-12-04 03:29, Jürgen Groß wrote:
> On 04.12.24 09:24, Penny Zheng wrote:
>> From: Roger Pau Monné <roger.pau@...rix.com>
>>
>> When running as a PVH dom0 the ACPI MADT is crafted by Xen in order to
>> report the correct numbers of vCPUs that dom0 has, so the host MADT is
>> not provided to dom0.  This creates issues when parsing the power and
>> performance related data from ACPI dynamic tables, as the ACPI
>> Processor UIDs found on the dynamic code are likely to not match the
>> ones crafted by Xen in the dom0 MADT.
>>
>> Xen would rely on Linux having filled at least the power and
>> performance related data of the vCPUs on the system, and would clone
>> that information in order to setup the remaining pCPUs on the system
>> if dom0 vCPUs < pCPUs.  However when running as PVH dom0 it's likely
>> that none of dom0 CPUs will have the power and performance data
>> filled, and hence the Xen ACPI Processor driver needs to fetch that
>> information by itself.
>>
>> In order to do so correctly, introduce a new helper to fetch the _CST
>> data without taking into account the system capabilities from the
>> CPUID output, as the capabilities reported to dom0 in CPUID might be
>> different from the ones on the host.
>>
>> Note that the newly introduced code will only fetch the _CST, _PSS,
>> _PPC and _PCT from a single CPU, and clone that information for all the
>> other Processors.  This won't work on an heterogeneous system with
>> Processors having different power and performance related data between
>> them.
>>
>> Signed-off-by: Roger Pau Monné <roger.pau@...rix.com>
>> Signed-off-by: Jason Andryuk <jason.andryuk@....com>
> 
> I think this is the V2 version of Jason's patch, of which he sent V3 just
> yesterday?

Penny's patch has some of the changes I made, but then I made an 
additional change and didn't tell her about it.

> Please sync with him how to proceed: is his patch meant to be a 
> prerequisite
> for your series or a part of it?

Sorry for the confusion.  Penny, I think you should just grab my v3 
(https://lore.kernel.org/xen-devel/20241203225338.1336-1-jason.andryuk@amd.com/T/#u) 
and resubmit with that.  It removes a BUG_ON that checkpatch complained 
about (which is unreachable because of an earlier NULL check).

Thanks,
Jason