Re: [Xen-users] NUMA nodes and cpu layout

[Stefan Kadow <stefan.kadow@xxxxxxxxx>]

Am 15.06.2018 um 09:00 schrieb George Dunlap:
> On Thu, Jun 14, 2018 at 11:19 PM, Stefan Kadow <stefan.kadow@xxxxxxxxx> wrote:
>> Hello,
>>
>> I have installed Debian 9.4 Stretch (stable) with Xen Hypervisor 4.8
>> (package from repository) on a NUMA machine with two AMD Epyc processors.
>>
>> When booting the default Debian kernel, the command "numactl --hardware"
>> returns the following:
>> available: 8 nodes (0-7)
>> node 0 cpus: 0 1 2 3 32 33 34 35
>> node 0 size: 0 MB
>> node 0 free: 0 MB
>> node 1 cpus: 4 5 6 7 36 37 38 39
>> node 1 size: 32170 MB
>> node 1 free: 31758 MB
>> node 2 cpus: 8 9 10 11 40 41 42 43
>> node 2 size: 0 MB
>> node 2 free: 0 MB
>> ...
>>
>> But when booting the Xen Kernel, the command "xl cpupool-numa-split"
>> returns another layout for cpus and nodes:
>> Name               CPU list
>> Pool-node0         0,1,2,3,4,5,6,7
>> Pool-node1         8,9,10,11,12,13,14,15
>> Pool-node2         16,17,18,19,20,21,22,23
>> ...
>>
>> Shouldn't the layout be the same?
> 
> No, because the numbers don't mean the same thing.  numactl seems to
> be reporting the ACPI IDs of the various logical processors, but ACPI
> often gives you nonsensical numbers like you see there -- nodes as
> high as 43 even though there are actually only 24 logical cpus,
> disjoint sets of numbers for the same node, &c.

This was just an excerpt, I did not want to post the whole list of all
64 CPUs, sorry. So there are no holes in the numer sequence.


> Xen uses its own numbering scheme, which is designed to be a bit more
> rational: hyperthreads are always next to each other, cores are
> contiguous, no holes in the number sequence.
> 
> The long and the short of it is: When using Xen tools, use the numbers
> reported by `xl info`.  When using numactl, use numbers reported by
> numactl.

Fine, then I will trust the output of Xen tools.

>  -George
> 
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Thanks for your quick answer!

--
Stefan

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