[nova][ptg] pinned and unpinned CPUs in one instance

Wang, Huaqiang huaqiang.wang at intel.com
Mon Nov 11 11:58:27 UTC 2019



> -----Original Message-----
> From: Bal√°zs Gibizer <balazs.gibizer at est.tech>
> Sent: Friday, November 8, 2019 3:10 PM
> To: openstack-discuss <openstack-discuss at lists.openstack.org>
> Subject: [nova][ptg] pinned and unpinned CPUs in one instance
> 
> spec: https://review.opendev.org/668656
> 
> Agreements from the PTG:
> 
> How we will test it:
> * do functional test with libvirt driver, like the pinned cpu tests we have
> today
> * donyd's CI supports nested virt so we can do pinned cpu testing but not
> realtime. As this CI is still work in progress we should not block on this.
> * coverage inhttps://opendev.org/x/whitebox-tempest-pluginis a nice to
> have
> 
> Naming: use the 'shared' and 'dedicated' terminology
> 
> Support both the hw:pinvcpus=3 and the resources:PCPU=2 flavor extra
> specs syntaxtbut not in the same flavor. The resources:PCPU=2 syntax will
> have less expression power until nova models NUMA in placement. So nova
> will try to evenly distribute PCPUs between numa nodes. If it not possible we
> reject the request and ask the user to use the
> hw:pinvcpus=3 syntax.
> 
> Realtime mask is an exclusion mask, any vcpus not listed there has to be in
> the dedicated set of the instance.
> 
> TODOInvestigate whether we want to enable NUMA by default
> * Pros: Simpler, everything is NUMA by default
> * Cons: We'll either have to break/make configurablethe 1:1 guest:host
> NUMA mapping else we won't be able to boot e.g. a 40 core shared instance
> on a 40 core, 2 NUMA node host

For the case of 'booting a 40 core shared instance on 40 core 2NUMA node' that will
not be covered by the new 'mixed' policy. It is just a legacy 'shared' instance with no
assumption about instance NUMA topology. 

By the way if you want a 'shared' instance, with 40 cores, to be scheduled on a host
of 40cores, 2 NUMA nodes, you also need to register all host cores as 'shared' cpus
through 'conf.compute.cpu_shared_set'. 

For instance with 'mixed' policy, what I want to propose is the instance should
demand at least one 'dedicated'(or PCPU) core. Thus, any 'mixed' instance or 'dedicated'
instance will not be scheduled one this host due to no PCPU available on this host.

And also, a 'mixed' instance should also demand at least one 'shared' (or VCPU) core.
a 'mixed' instance demanding all cores from PCPU resource should be considered as
an invalid one. And an instance demanding all cores from PCPU resource is just a
legacy 'dedicated' instance, which CPU allocation policy is 'dedicated'.

In conclusion,  a instance with the policy of 'mixed' 
-. demands at least one 'dedicated' cpu and at least one 'shared' cpu. 
-. with NUMA topology by default due to requesting pinned cpu

In my understanding the cons does not exist by making above rules. 

Br
Huaqiang

> 
> 
> Cheers,
> gibi
> 
> 




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