[openstack-dev] [openstack-dev[[nova] Simple question about sorting CPU topologies

Jay Pipes jaypipes at gmail.com
Tue Jun 20 16:58:44 UTC 2017

On 06/20/2017 12:53 PM, Chris Friesen wrote:
> On 06/20/2017 06:29 AM, Jay Pipes wrote:
>> On 06/19/2017 10:45 PM, Zhenyu Zheng wrote:
>>> Sorry, The mail sent accidentally by mis-typing ...
>>> My question is, what is the benefit of the above preference?
>> Hi Kevin!
>> I believe the benefit is so that the compute node prefers CPU 
>> topologies that do
>> not have hardware threads over CPU topologies that do include hardware 
>> threads.
>> I'm not sure exactly of the reason for this preference, but perhaps it 
>> is due to
>> assumptions that on some hardware, threads will compete for the same 
>> cache
>> resources as other siblings on a core whereas cores may have their own 
>> caches
>> (again, on some specific hardware).
> Isn't the definition of hardware threads basically the fact that the 
> sibling threads share the resources of a single core?
> Are there architectures that OpenStack runs on where hardware threads 
> don't compete for cache/TLB/execution units?  (And if there are, then 
> why are they called threads and not cores?)

I've learned over the years not to make any assumptions about hardware.

Thus my "not sure exactly" bet-hedging ;)


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