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[Matt Riedemann <mriedem@xxxxxxxxxx>]

** Also affects: nova/newton
   Importance: Undecided
       Status: New

** Changed in: nova/newton
     Assignee: (unassigned) => Stephen Finucane (stephenfinucane)

** Changed in: nova/newton
       Status: New => In Progress

** Changed in: nova/newton
   Importance: Undecided => Medium

** Changed in: nova
     Assignee: Vladik Romanovsky (vladik-romanovsky) => Stephen Finucane (stephenfinucane)

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https://bugs.launchpad.net/bugs/1578155

Title:
  'hw:cpu_thread_policy=prefer' misbehaviour

Status in OpenStack Compute (nova):
  Fix Released
Status in OpenStack Compute (nova) newton series:
  In Progress

Bug description:
  Description
  ===========

  'hw:cpu_thread_policy=prefer' allocates vCPUs in pairs of sibling
  threads properly. An odd number of vCPUs will allocate pairs and a
  single one. That single one should not be isolated. So 20 available
  threads, shall be able to allocate 4 VMs of 5 vCPUs. When booting up
  the third VM, it is giving an error.

  Steps to reproduce
  ==================

  1.- Creating a flavor:

  nova flavor-create pinning auto 1024 10 5
  nova flavor-key pinning set hw:cpu_policy=dedicated
  nova flavor-key pinning set hw:cpu_thread_policy=prefer
  nova flavor-key pinning set hw:numa_nodes=1

  2.- Booting up simple VMs:

  nova boot testPin1 --flavor pinning --image cirros --nic net-
  id=$NET_ID

  In my setup, I have 20 available threads:

    NUMANode L#0 (P#0 32GB)
      Socket L#0 + L3 L#0 (15MB)
        L2 L#0 (256KB) + L1d L#0 (32KB) + L1i L#0 (32KB) + Core L#0
          PU L#0 (P#0)
          PU L#1 (P#12)
        L2 L#1 (256KB) + L1d L#1 (32KB) + L1i L#1 (32KB) + Core L#1
          PU L#2 (P#2)
          PU L#3 (P#14)
        L2 L#2 (256KB) + L1d L#2 (32KB) + L1i L#2 (32KB) + Core L#2
          PU L#4 (P#4)
          PU L#5 (P#16)
        L2 L#3 (256KB) + L1d L#3 (32KB) + L1i L#3 (32KB) + Core L#3
          PU L#6 (P#6)
          PU L#7 (P#18)
        L2 L#4 (256KB) + L1d L#4 (32KB) + L1i L#4 (32KB) + Core L#4
          PU L#8 (P#8)
          PU L#9 (P#20)
        L2 L#5 (256KB) + L1d L#5 (32KB) + L1i L#5 (32KB) + Core L#5
          PU L#10 (P#10)
          PU L#11 (P#22)

    NUMANode L#1 (P#1 32GB) + Socket L#1 + L3 L#1 (15MB)
      L2 L#6 (256KB) + L1d L#6 (32KB) + L1i L#6 (32KB) + Core L#6
        PU L#12 (P#1)
        PU L#13 (P#13)
      L2 L#7 (256KB) + L1d L#7 (32KB) + L1i L#7 (32KB) + Core L#7
        PU L#14 (P#3)
        PU L#15 (P#15)
      L2 L#8 (256KB) + L1d L#8 (32KB) + L1i L#8 (32KB) + Core L#8
        PU L#16 (P#5)
        PU L#17 (P#17)
      L2 L#9 (256KB) + L1d L#9 (32KB) + L1i L#9 (32KB) + Core L#9
        PU L#18 (P#7)
        PU L#19 (P#19)
      L2 L#10 (256KB) + L1d L#10 (32KB) + L1i L#10 (32KB) + Core L#10
        PU L#20 (P#9)
        PU L#21 (P#21)
      L2 L#11 (256KB) + L1d L#11 (32KB) + L1i L#11 (32KB) + Core L#11
        PU L#22 (P#11)
        PU L#23 (P#23)

  Using the cpu_thread_policy:prefer, the behaviour is ok for the first
  two VMs. So 5 threads are allocated in pairs.

  [root@nfvsdn-04 ~(keystone_admin)]# virsh vcpupin 2
  VCPU: CPU Affinity
  ----------------------------------
     0: 10
     1: 22
     2: 16
     3: 4
     4: 8

  [root@nfvsdn-04 ~(keystone_admin)]# virsh vcpupin 3
  VCPU: CPU Affinity
  ----------------------------------
     0: 17
     1: 5
     2: 3
     3: 15
     4: 11

  However, eventhough there are enough threads in order to allocate
  another 2 VMs with the same flavor, I get the following error booting
  up the third VM:

  INFO nova.filters Filtering removed all hosts for the request with
  instance ID 'cbb53e29-a7da-4c14-a3ad-4fb3aa04f101'. Filter results:
  ['RetryFilter: (start: 1, end: 1)', 'AvailabilityZoneFilter: (start:
  1, end: 1)', 'RamFilter: (start: 1, end: 1)', 'C[r│omputeFilter:
  (start: 1, end: 1)', 'ComputeCapabilitiesFilter: (start: 1, end: 1)',
  'ImagePropertiesFilter: (start: 1, end: 1)', 'CoreFilter: (start: 1,
  end: 1)', 'NUMATopologyFilter: (start: 1, endo: 0)']

  
  There should be enough space for 4 VMs allocated with cpu_thread_policy=prefer flavor.

  Expected result
  ===============

  To have 4 VMs up&running with flavor 'pinning'.

  Actual result
  =============

  3rd VM fails at scheduling.

  Environment
  ==========

  All-in-one environment.

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