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[nova][ironic][ptg] Resource tracker scaling issues


On 11/11/2019 7:03 AM, Chris Dent wrote:
> Or using
> separate processes? For the ironic and vsphere contexts, increased
> CPU usage by the nova-compute process does not impact on the
> workload resources, so parallization is likely a good option.

I don't know how much it would help - someone would have to actually 
test it out and get metrics - but one easy win might just be using a 
thread or process executor pool here [1] so that N compute nodes could 
be processed through the update_available_resource periodic task 
concurrently, maybe $ncpu or some factor thereof. By default make it 
serialized for backward compatibility and non-ironic deployments. Making 
that too highly concurrent could have negative impacts on other things 
running on that host, like the neutron agent, or potentially storming 
conductor/rabbit with a ton of DB requests from that compute.

That doesn't help with the scenario that the big 
COMPUTE_RESOURCE_SEMAPHORE lock is held by the periodic task while 
spawning, moving, or deleting an instance that also needs access to the 
big lock to update the resource tracker, but baby steps if any steps in 
this area of the code would be my recommendation.

[1] 
https://github.com/openstack/nova/blob/20.0.0/nova/compute/manager.py#L8629

-- 

Thanks,

Matt