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[Chris Friesen <chris.friesen@xxxxxxxxxxxxx>]

Public bug reported:

Currently in the NUMA topology case (so multi-node guest, dedicated
CPUs, hugepages in the guest, etc.) a single guest is not allowed to
consume more CPU/RAM than the host actually has in total regardless of
the specified overcommit ratio.  In other words, the overcommit ratio
only applies when the host resources are being used by multiple guests.
A given host resource can only be used once by any particular guest.

So as an example, if the host has 2 pCPUs in total for guests, a single
guest instance is not allowed to use more than 2CPUs but you might be
able to have 16 such instances running. (Assuming default CPU overcommit
ratio.)

However, this is not true when the NUMA topology is not involved.  In
that case a host with 2 pCPUs would allow a guest with 3 vCPUs to be
spawned.

We should pick one behaviour as "correct" and adjust the other one to
match.  Given that the NUMA topology case was discussed more recently,
it seems reasonable to select it as the "correct" behaviour.

** Affects: nova
     Importance: Undecided
         Status: New


** Tags: compute scheduler

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https://bugs.launchpad.net/bugs/1485631

Title:
  CPU/RAM overcommit treated differently by "normal" and "NUMA topology"
  case

Status in OpenStack Compute (nova):
  New

Bug description:
  Currently in the NUMA topology case (so multi-node guest, dedicated
  CPUs, hugepages in the guest, etc.) a single guest is not allowed to
  consume more CPU/RAM than the host actually has in total regardless of
  the specified overcommit ratio.  In other words, the overcommit ratio
  only applies when the host resources are being used by multiple
  guests.  A given host resource can only be used once by any particular
  guest.

  So as an example, if the host has 2 pCPUs in total for guests, a
  single guest instance is not allowed to use more than 2CPUs but you
  might be able to have 16 such instances running. (Assuming default CPU
  overcommit ratio.)

  However, this is not true when the NUMA topology is not involved.  In
  that case a host with 2 pCPUs would allow a guest with 3 vCPUs to be
  spawned.

  We should pick one behaviour as "correct" and adjust the other one to
  match.  Given that the NUMA topology case was discussed more recently,
  it seems reasonable to select it as the "correct" behaviour.

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