Re: [RFC PATCH] arm64: topology: Map PPTT node offset to logic physical package id

[Sudeep Holla <sudeep.holla@arm.com>]

On 28/06/18 12:57, Andrew Jones wrote:
> On Thu, Jun 28, 2018 at 10:38:24AM +0100, Sudeep Holla wrote:
>> Hi Shunyong,
>>
>> On 28/06/18 10:18, Shunyong Yang wrote:
>>> As PPTT spec doesn't define the physical package id,
>>> find_acpi_cpu_topology_package() will return offset of the node with
>>> Physical package field set when querying physical package id. So, it
>>> returns 162(0xA2) in following example.
>>>
>>> [0A2h 0162   1]                Subtable Type : 00 [Processor Hierarchy
>>> Node]
>>> [0A3h 0163   1]                       Length : 1C
>>> [0A4h 0164   2]                     Reserved : 0000
>>> [0A6h 0166   4]        Flags (decoded below) : 00000003
>>>                             Physical package : 1
>>>                      ACPI Processor ID valid : 1
>>> [0AAh 0170   4]                       Parent : 00000000
>>> [0AEh 0174   4]            ACPI Processor ID : 00001000
>>> [0B2h 0178   4]      Private Resource Number : 00000002
>>> [0B6h 0182   4]             Private Resource : 0000006C
>>> [0BAh 0186   4]             Private Resource : 00000084
>>>
>>> So, when "cat physical_package" in /sys/devices/system/cpu/cpu0/topology/,
>>> it will output 162(0xA2). And if some items are added before the node
>>> above, the output will change to other value.
>>>
>>> This patch maps the node offset to a logic package id. It maps the first
>>> node offset to 0, the second to 1, and so on.
>>>
>>> Then, it will not output a big value, such as 162 above. And it will
>>> not change when some nodes(Physical package not set) are added.
>>>
>>> And as long as the nodes with Physical package field set in PPTT keeps
>>> the real hardware order, the logic id can map to hardware package id to
>>> some extent.
>>>
>>> Hope to get feedback from you.
>>
>> Thanks for the patch, but Andrew Jones has also posted a patch[1] which
>> I had a look but was not sure what is the best approach to fix it yet.
>> I will think about it and respond to that.
>>
> 
> I'll send a v1 yet today. The RFC version was actually OK, as the concern
> with ACPI nodes not being in the expected order wasn't actually a problem.
> The thread-id or core-id would only be reset to zero when a yet to be
> remapped core-id (and all its peers) was found when iterating the PEs.
> Since all peers were handled at the same time, the counter reset was
> correct, even when the ACPI nodes were out-of-order. The code didn't make
> that very obvious, though, and there was some room for other cleanups,
> so I've reworked it. Once I run it through a couple more rounds of testing
> I'll repost.
> 

OK sure. I liked the approach in Shunyong's patch. I was thinking if we
can avoid the list and dynamic allocation on each addition and make it
more simpler.

-- 
Regards,
Sudeep