Messages in this thread | | | Subject | Re: [RFC PATCH] arm64: topology: Map PPTT node offset to logic physical package id | From | Jeremy Linton <> | Date | Thu, 28 Jun 2018 08:19:26 -0500 |
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Hi,
On 06/28/2018 07:12 AM, Sudeep Holla wrote: > > > 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. >
This one reads simpler, but yes I agree we should try to avoid the dynamic allocation.
OTOH, I think that dropping the dynamic allocation leads to an algorithm that picks a value and replaces all the matches. Which of course is Andrew's patch, although I did have to read it a couple times to get a grasp how it works. I'm guessing that is due to the fact that he seems to have optimized 3 double loops into a single loop with two individual nested loops. AKA its probably more efficient than the naive implementation, but readability seems to have suffered a bit in the initial version he posted. I'm not sure the optimization is worth it, but I'm guessing there is a middle ground which makes it more readable.
Finally, @Shunyong, thanks for putting the effort into this...
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