[openstack-dev] [nova] A prototype implementation towards the "shared state scheduler"

Jay Pipes jaypipes at gmail.com
Tue Feb 23 23:49:14 UTC 2016

On 02/23/2016 06:03 PM, Chris Friesen wrote:
> On 02/21/2016 01:56 PM, Jay Pipes wrote:
>> Yingxin, sorry for the delay in responding to this thread. My comments
>> inline.
>> On 02/17/2016 12:45 AM, Cheng, Yingxin wrote:
>>> To better illustrate the differences between shared-state,
>>> resource-provider and legacy scheduler, I’ve drew 3 simplified pictures
>>> [1] in emphasizing the location of resource view, the location of claim
>>> and resource consumption, and the resource update/refresh pattern in
>>> three kinds of schedulers. Hoping I’m correct in the “resource-provider
>>> scheduler” part.
>> 2) Claims of resource amounts are done in a database transaction
>> atomically
>> within each scheduler process. Therefore there are no "cache updates"
>> arrows
>> going back from compute nodes to the resource-provider DB. The only
>> time a
>> compute node would communicate with the resource-provider DB (and thus
>> the
>> scheduler at all) would be in the case of a *failed* attempt to
>> initialize
>> already-claimed resources.
> Can you point me to the BP/spec that talks about this?  Where in the
> code would we update the DB to reflect newly-freed resources?

I should have been more clear, sorry. I am referring only to the process 
of claiming resources and the messages involved in cache updates for 
those claims. I'm not referring to freeing resources (i.e. an instance 
termination). In those cases, there would still need to be a message 
sent to inform the scheduler that the resources had been freed. Nothing 
would change in that regard.

For information, the blueprint where we are discussing moving claims to 
the scheduler (and away from the compute nodes) is here:


I'm in the process of splitting the above blueprint into two. One will 
be for the proposed moving of the filters from the scheduler Python 
process to instead by filters on the database query for compute nodes. 
Another blueprint will be for the "move the claims to the scheduler" stuff.


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