CPU constraints

[Kapil Thangavelu]

On Thu, Sep 27, 2012 at 1:06 PM, Martin Packman <
martin.packman at canonical.com> wrote:

> What do juju users want from a cpu constraint on instances?
>
> I'm adding support in MaaS, and have some choices on what the number
> means exactly.
>
> <
> http://docs.openstack.org/api/openstack-compute/2/content/Get_Flavor_Details-d1e4317.html
> >
>
> For OpenStack, 'vcpus' is used, which (though not clearly documented?)
> is the number of cores the instance has.
>
> <http://aws.amazon.com/ec2/instance-types/>
>
> In EC2 abstract 'compute units' are used, which they correspond
> approximately to 1.0-1.2 GHz processors from 2007. However, the
> documentation pushes you towards benchmarking on different instance
> types over than treating these numbers too seriously.
>
> So, either presenting the number of cpus, or the total GHz, seem like
> reasonable options. Which would you find more useful in general? Using
> tags in MaaS can constrain on more precise details regardless.
>
>
Its an interesting question, previously when constraints were being
formulated, one idea was that we'd have a simple benchmark program that
could give some approximation of a notional linear scale roughly
corresponding to an ec2 unit given a cpu intensive workload, except via the
benchmark in a cross provider fashion. This a fairly naive approach that
occludes alot of the variations across architectures and versions there of
and workloads as well, but is nice for its simplicity. Ie. python -m
test.pystone with a different normalization. For now (ie delivering generic
constraints for 12.10) i would suggest pursuing the even more naive
approach of openstack and just use cpu core count. additional facilities
around gpu compute facilities, processor family, etc would be nice to
expose as a base set of automatic maas tags.

cheers,

Kapil
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