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[Tetsuro Nakamura <nakamura.tetsuro@xxxxxxxxxxxxx>]

Public bug reported:

In bug/1744965(https://bugs.launchpad.net/nova/+bug/1744965), it is
reported that the way emulator_threads_policy allocates the extra cpu
resource for emulator is not optimal.

This report reports the bug also stays when `cpu_thread_policy=isolate`.

The instance I use for testing is a 3-vcpu VM with
`cpu_thread_policy=isolate`; before enable this emulator_threads_policy,
I reserve 6 cpu (actually 6 threads since we enable hyper threading) in
nova config,

 vcpu_pin_set=8,10,12,32,34,36

Now when we enable emulator_threads_policy, in stead of adding one more
thread to this vcpu pin list in the nova config, I end up adding two
more sibling threads (on the same core)

 vcpu_pin_set=8,10,12,16,32,34,36,40

So I ended up using 2 more threads, but only one of them is used for
emulator and the other thread is wasted.

** Affects: nova
     Importance: Undecided
         Status: New

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https://bugs.launchpad.net/bugs/1746393

Title:
  'cpu_thread_policy' impacts on emulator threads

Status in OpenStack Compute (nova):
  New

Bug description:
  In bug/1744965(https://bugs.launchpad.net/nova/+bug/1744965), it is
  reported that the way emulator_threads_policy allocates the extra cpu
  resource for emulator is not optimal.

  This report reports the bug also stays when
  `cpu_thread_policy=isolate`.

  The instance I use for testing is a 3-vcpu VM with
  `cpu_thread_policy=isolate`; before enable this
  emulator_threads_policy, I reserve 6 cpu (actually 6 threads since we
  enable hyper threading) in nova config,

   vcpu_pin_set=8,10,12,32,34,36

  Now when we enable emulator_threads_policy, in stead of adding one
  more thread to this vcpu pin list in the nova config, I end up adding
  two more sibling threads (on the same core)

   vcpu_pin_set=8,10,12,16,32,34,36,40

  So I ended up using 2 more threads, but only one of them is used for
  emulator and the other thread is wasted.

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