Re: [PATCH v8 5/8] hw/acpi/aml-build: Add PPTT table

[Eric Auger]

Hi,
On 10/20/21 2:27 PM, wangyanan (Y) wrote:
> Hi Eric,
> 
> On 2021/10/20 19:11, Eric Auger wrote:
>> Hi Yanan,
>> On 10/20/21 11:51 AM, wangyanan (Y) wrote:
>>> Hi Eric,
>>>
>>> On 2021/10/20 16:02, Eric Auger wrote:
>>>> Hi,
>>>>
>>>> On 10/14/21 3:22 PM, Yanan Wang wrote:
>>>>> From: Andrew Jones <drjones@redhat.com>
>>>>>
>>>>> Add the Processor Properties Topology Table (PPTT) used to
>>>>> describe CPU topology information to ACPI guests.
>>>>>
>>>>> Note, a DT-boot Linux guest with a non-flat CPU topology will
>>>>> see socket and core IDs being sequential integers starting
>>>>> from zero, which is different from ACPI-boot Linux guest,
>>>>> e.g. with -smp 4,sockets=2,cores=2,threads=1
>>>>>
>>>>> a DT boot produces:
>>>>>
>>>>>    cpu:  0 package_id:  0 core_id:  0
>>>>>    cpu:  1 package_id:  0 core_id:  1
>>>>>    cpu:  2 package_id:  1 core_id:  0
>>>>>    cpu:  3 package_id:  1 core_id:  1
>>>>>
>>>>> an ACPI boot produces:
>>>>>
>>>>>    cpu:  0 package_id: 36 core_id:  0
>>>>>    cpu:  1 package_id: 36 core_id:  1
>>>>>    cpu:  2 package_id: 96 core_id:  2
>>>>>    cpu:  3 package_id: 96 core_id:  3
>>>>>
>>>>> This is due to several reasons:
>>>>>
>>>>>    1) DT cpu nodes do not have an equivalent field to what the PPTT
>>>>>       ACPI Processor ID must be, i.e. something equal to the MADT CPU
>>>>>       UID or equal to the UID of an ACPI processor container. In both
>>>>>       ACPI cases those are platform dependant IDs assigned by the
>>>>>       vendor.
>>>>>
>>>>>    2) While QEMU is the vendor for a guest, if the topology specifies
>>>>>       SMT (> 1 thread), then, with ACPI, it is impossible to assign a
>>>>>       core-id the same value as a package-id, thus it is not possible
>>>>>       to have package-id=0 and core-id=0. This is because package and
>>>>>       core containers must be in the same ACPI namespace and therefore
>>>>>       must have unique UIDs.
>>>>>
>>>>>    3) ACPI processor containers are not mandatorily required for PPTT
>>>>>       tables to be used and, due to the limitations of which IDs are
>>>>>       selected described above in (2), they are not helpful for QEMU,
>>>>>       so we don't build them with this patch. In the absence of them,
>>>>>       Linux assigns its own unique IDs. The maintainers have chosen
>>>>> not
>>>>>       to use counters from zero, but rather ACPI table offsets, which
>>>>>       explains why the numbers are so much larger than with DT.
>>>>>
>>>>>    4) When there is no SMT (threads=1) the core IDs for ACPI boot
>>>>> guests
>>>>>       match the logical CPU IDs, because these IDs must be equal to
>>>>> the
>>>>>       MADT CPU UID (as no processor containers are present), and QEMU
>>>>>       uses the logical CPU ID for these MADT IDs.
>>>>>
>>>>> So in summary, with QEMU as the vendor for the guests, we simply
>>>>> use sequential integers starting from zero for the non-leaf nodes
>>>>> but with ID-valid flag unset, so that guest will ignore them and
>>>>> use table offsets as unique container IDs. And we use logical CPU
>>>>> IDs for the leaf nodes with the ID-valid flag set, which will be
>>>>> consistent with MADT.
>>>>>
>>>>> Signed-off-by: Andrew Jones <drjones@redhat.com>
>>>>> Co-developed-by: Yanan Wang <wangyanan55@huawei.com>
>>>>> Signed-off-by: Yanan Wang <wangyanan55@huawei.com>
>>>>> Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
>>>>> ---
>>>>>    hw/acpi/aml-build.c         | 60
>>>>> +++++++++++++++++++++++++++++++++++++
>>>>>    include/hw/acpi/aml-build.h |  3 ++
>>>>>    2 files changed, 63 insertions(+)
>>>>>
>>>>> diff --git a/hw/acpi/aml-build.c b/hw/acpi/aml-build.c
>>>>> index b7b9db6888..0d50e88e9d 100644
>>>>> --- a/hw/acpi/aml-build.c
>>>>> +++ b/hw/acpi/aml-build.c
>>>>> @@ -1990,6 +1990,66 @@ void build_processor_hierarchy_node(GArray
>>>>> *tbl, uint32_t flags,
>>>>>        }
>>>>>    }
>>>>>    +/* ACPI 6.2: 5.2.29 Processor Properties Topology Table (PPTT) */
>>>>> +void build_pptt(GArray *table_data, BIOSLinker *linker, MachineState
>>>>> *ms,
>>>>> +                const char *oem_id, const char *oem_table_id)
>>>>> +{
>>>>> +    int pptt_start = table_data->len;
>>>>> +    int uid = 0;
>>>>> +    int socket;
>>>>> +    AcpiTable table = { .sig = "PPTT", .rev = 2,
>>>>> +                        .oem_id = oem_id, .oem_table_id =
>>>>> oem_table_id };
>>>> Table 5-149 of 6.2 spec (6.2 May 2017) tells the rev shall be 1. Or is
>>>> it an erratum somewhere I did miss?
>>> Yes, the revision in 6.2 spec is 1. And it's 2 in spec 6.3.
>>> So just to be sure, should I use the oldest revision ?
>> If you need (and use) features (such as flags) introduced in 6.3 then
>> you should say the code complies with 6.3 and update the above comment.
> The comment /* ACPI 6.2: 5.2.29 Processor Properties Topology Table
> (PPTT) */
> tried to explain the first spec version where PPTT is introduced is 6.2.
> But it may
> adds some confusion. I think it's better to replace it with:
> /*
>  * ACPI spec 5.2.29 Processor Properties Topology Table (PPTT)
>  * (Revision 6.2 or later)
>  */
> 
> just like our build_slit().
That's not my understanding. I think we usually point to the latest spec
revision you comply with, ie. in that case 6.3 chapter ...

Thanks

Eric
>>>> I would also add the spec version in the commit msg.
>>>>> +
>>>>> +    acpi_table_begin(&table, table_data);
>>>>> +
>>>>> +    for (socket = 0; socket < ms->smp.sockets; socket++) {
>>>>> +        uint32_t socket_offset = table_data->len - pptt_start;
>>>>> +        int core;
>>>>> +
>>>>> +        build_processor_hierarchy_node(
>>>>> +            table_data,
>>>>> +            /*
>>>>> +             * ACPI 6.2 - Physical package
>>>>> +             * represents the boundary of a physical package
>>>>> +             */
>>>>> +            (1 << 0),
>>>>> +            0, socket, NULL, 0);
>>>> I see we set an ACPI process ID but in the meantime the ACPI processor
>>>> ID valid flag is not set. I am not sure I fully catch the meaning of
>>>> this latter but just to double check if this is done on purpose.
>>> Yes, it's on purpose.
>>>> Maybe
>>>> wort a general comment as this also happens below.
>>> The ID of the container node is invalid and ID of the leaf node is
>>> valid.
>>> The commit message by Andrew has explained why (reason 3). I think
>>> it may be clear enough to explain there why we don't need a valid ID
>>> for the container node.
>>>>> +
>>>>> +        for (core = 0; core < ms->smp.cores; core++) {
>>>>> +            uint32_t core_offset = table_data->len - pptt_start;
>>>>> +            int thread;
>>>>> +
>>>>> +            if (ms->smp.threads > 1) {
>>>>> +                build_processor_hierarchy_node(
>>>>> +                    table_data,
>>>>> +                    /*
>>>>> +                     * ACPI 6.2 - Physical package
>>>>> +                     * doesn't represent the boundary of a physical
>>>>> package
>>>>> +                     */
>>>>> +                    (0 << 0),
>>>> would rather say (0 << 0) /* not a physical package */ and same
>>>> elsewhere
>>> Ok, thanks.
>>>>> +                    socket_offset, core, NULL, 0);
>>>>> +
>>>>> +                for (thread = 0; thread < ms->smp.threads;
>>>>> thread++) {
>>>>> +                    build_processor_hierarchy_node(
>>>>> +                        table_data,
>>>>> +                        (1 << 1) | /* ACPI 6.2 - ACPI Processor ID
>>>>> valid */
>>>>> +                        (1 << 2) | /* ACPI 6.3 - Processor is a
>>>>> Thread */
>>>> So the references look globaly confusing to me. Either it complies to
>>>> 6.2 or to 6.3. Looks ir rather complies with 6.3. To me, this needs to
>>>> be clarified.
>>> ACPI 6.2 in the comment means the flag is introduced in the spec
>>> since 6.2.
>>> The same, ACPI 6.3 means the flag is introduced since 6.3. Maybe I
>>> should
>>> just drop all the version-prefix in the comment ?
>> Yes I think you can drop those comments and just upgrade the global
>> compliance with 6.3
>>
> I will drop the prefix and keep the rest. And add a generic comment on
> top of build_pptt() as I replied above.
> 
> Thanks,
> Yanan
>>>> I would also add the reference it complies to in the
>>>> commit msg.
>>> Ok, sure.
>>>
>>> Thanks,
>>> Yanan
>>> .
>>>>> +                        (1 << 3),  /* ACPI 6.3 - Node is a Leaf */
>>>>> +                        core_offset, uid++, NULL, 0);
>>>>> +                }
>>>>> +            } else {
>>>>> +                build_processor_hierarchy_node(
>>>>> +                    table_data,
>>>>> +                    (1 << 1) | /* ACPI 6.2 - ACPI Processor ID
>>>>> valid */
>>>>> +                    (1 << 3),  /* ACPI 6.3 - Node is a Leaf */
>>>>> +                    socket_offset, uid++, NULL, 0);
>>>>> +            }
>>>>> +        }
>>>>> +    }
>>>>> +
>>>>> +    acpi_table_end(linker, &table);
>>>>> +}
>>>>> +
>>>>>    /* build rev1/rev3/rev5.1 FADT */
>>>>>    void build_fadt(GArray *tbl, BIOSLinker *linker, const AcpiFadtData
>>>>> *f,
>>>>>                    const char *oem_id, const char *oem_table_id)
>>>>> diff --git a/include/hw/acpi/aml-build.h b/include/hw/acpi/aml-build.h
>>>>> index 2c457c8f17..b92706388c 100644
>>>>> --- a/include/hw/acpi/aml-build.h
>>>>> +++ b/include/hw/acpi/aml-build.h
>>>>> @@ -493,6 +493,9 @@ void build_processor_hierarchy_node(GArray *tbl,
>>>>> uint32_t flags,
>>>>>                                        uint32_t parent, uint32_t id,
>>>>>                                        uint32_t *priv_rsrc, uint32_t
>>>>> priv_num);
>>>>>    +void build_pptt(GArray *table_data, BIOSLinker *linker,
>>>>> MachineState *ms,
>>>>> +                const char *oem_id, const char *oem_table_id);
>>>>> +
>>>>>    void build_fadt(GArray *tbl, BIOSLinker *linker, const AcpiFadtData
>>>>> *f,
>>>>>                    const char *oem_id, const char *oem_table_id);
>>>>>   
>>>> Thanks
>>>>
>>>> Eric
>>>>
>>>> .
>> .
>