I found the data in nova.compute_nodes.numa_topology is:

{"cells": 
    [{"nova_object.version": "1.2", 
       "nova_object.changes": 
                ["cpu_usage", "memory_usage", "cpuset", "pinned_cpus", "siblings", "memory", "mempages", "id"], 
        "nova_object.name": "NUMACell", 
        "nova_object.data": 
        {"cpu_usage": 12, "memory_usage": 10240, 
           "cpuset": [3, 4, 5, 6, 7, 8, 9, 23, 24, 25, 26, 27, 28, 29], 
           "pinned_cpus": [3, 4, 5, 7, 8, 9, 23, 24, 25, 27, 28, 29], 
           "siblings": [[25, 5], [8, 28], [9, 29], [24, 4], [27, 7], [3, 23], [26, 6]], 
           "memory": 31884, 
           "mempages": 
                        ......
                        ......

Which confused me is the siblings order: "siblings": [[25, 5], [8, 28], [9, 29], [24, 4], [27, 7], [3, 23], [26, 6]],

All the printout in the node shows:

root@compute-0-14:/var/lib/libvirt/images# lscpu | grep NUMA NUMA node(s): 2 NUMA node0 CPU(s): 0-9,20-29 NUMA node1 CPU(s): 10-19,30-39

capbilities shows, only 1 cell listed:

<topology>
  <cells num='2'>
    <cell id='0'>
      <memory unit='KiB'>32649544</memory>
      <pages unit='KiB' size='4'>7113810</pages>
      <pages unit='KiB' size='2048'>512</pages>
      <pages unit='KiB' size='1048576'>27</pages>
      <distances>
        <sibling id='0' value='10'/>
        <sibling id='1' value='20'/>
      </distances>
      <cpus num='20'>
        <cpu id='0' socket_id='0' core_id='0' siblings='0,20'/>
        <cpu id='1' socket_id='0' core_id='1' siblings='1,21'/>
        <cpu id='2' socket_id='0' core_id='2' siblings='2,22'/>
        <cpu id='3' socket_id='0' core_id='3' siblings='3,23'/>
        <cpu id='4' socket_id='0' core_id='4' siblings='4,24'/>
        <cpu id='5' socket_id='0' core_id='8' siblings='5,25'/>
        <cpu id='6' socket_id='0' core_id='9' siblings='6,26'/>
        <cpu id='7' socket_id='0' core_id='10' siblings='7,27'/>
        <cpu id='8' socket_id='0' core_id='11' siblings='8,28'/>
        <cpu id='9' socket_id='0' core_id='12' siblings='9,29'/>
        <cpu id='20' socket_id='0' core_id='0' siblings='0,20'/>
        <cpu id='21' socket_id='0' core_id='1' siblings='1,21'/>
        <cpu id='22' socket_id='0' core_id='2' siblings='2,22'/>
        <cpu id='23' socket_id='0' core_id='3' siblings='3,23'/>
        <cpu id='24' socket_id='0' core_id='4' siblings='4,24'/>
        <cpu id='25' socket_id='0' core_id='8' siblings='5,25'/>
        <cpu id='26' socket_id='0' core_id='9' siblings='6,26'/>
        <cpu id='27' socket_id='0' core_id='10' siblings='7,27'/>
        <cpu id='28' socket_id='0' core_id='11' siblings='8,28'/>
        <cpu id='29' socket_id='0' core_id='12' siblings='9,29'/>

nova.conf is:

vcpu_pin_set="3-18,23-38"

So could some expert can tell me why the siblings is organized in this order? With all the input shows the CPU from small to big. Thanks.