[openstack-dev] realtime kvm cpu affinities

Henning Schild henning.schild at siemens.com
Wed Jun 21 15:10:19 UTC 2017

Am Wed, 21 Jun 2017 09:32:42 -0400
schrieb Luiz Capitulino <lcapitulino at redhat.com>:

> On Wed, 21 Jun 2017 12:47:27 +0200
> Henning Schild <henning.schild at siemens.com> wrote:
> > > What is your solution?    
> > 
> > We have a kilo-based prototype that introduced emulator_pin_set in
> > nova.conf. All vcpu threads will be scheduled on vcpu_pin_set and
> > emulators and IO of all VMs will share emulator_pin_set.
> > vcpu_pin_set contains isolcpus from the host and emulator_pin_set
> > contains best-effort cores from the host.  
> You lost me here a bit as I'm not familiar with OpenStack
> configuration.

Does not matter, i guess you got the point and some other people might
find that useful.

> > That basically means you put all emulators and io of all VMs onto a
> > set of cores that the host potentially also uses for other stuff.
> > Sticking with the made up numbers from above, all the 0.05s can
> > share pcpus.  
> So, this seems to be way we use KVM-RT without OpenStack: emulator
> threads and io threads run on the host housekeeping cores, where all
> other host processes will run. IOW, you only reserve pcpus for vcpus
> threads.

Thanks for the input. I think you confirmend that the current
implementation in openstack can not work and that the new proposal and
our approach should work.
Now we will have to see how to proceed with that information in the
openstack community.

> I can't comment on OpenStack accounting trade-off/implications of
> doing this, but from KVM-RT perspective this is probably the best
> solution. I say "probably" because so far we have only tested with
> cyclictest and simple applications. I don't know if more complex
> applications would have different needs wrt I/O threads for example.

We have a networking ping/pong cyclictest kind of thing and much more
complex setups. Emulators and IO are not on the critical path in our

> PS: OpenStack devel list refuses emails from non-subscribers. I won't
>     subscribe for a one-time discussion, so my emails are not
>     reaching the list...

Yeah had the same problem, also with their gerrit. Lets just call it
Stack ... I kept all your text in my replies, and they end up on the


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