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Re: [Xen-devel] [PATCH RESEND 05/12] xen: numa-sched: make space for per-vcpu node-affinity

On mar, 2013-11-05 at 17:16 +0000, George Dunlap wrote:
> Just to outline what the alternative would look like:  The hypervisor 
> would focus on the minimum mechanisms required to do something useful 
> for NUMA systems.  The domain NUMA affinity would be only used for 
> memory allocation.  vcpus would only have "hard" and "soft" affinities. 
>   The toolstack (libxl? xl?) would be responsible for stitching these 
> together into a useable interface for NUMA: e.g., it would have the 
> concept of "numa affinity" for vcpus (or indeed, virtual NUMA 
> topologies), and would do things like update the domain NUMA affinity 
> based on vcpu affinities.
Yep, I confirm that I like it, and that I don't think this should be too
difficult to implement. The hardest thing is going to be picking up
sensible names for libxl functions and xl confing options (and no
simpley  here, because I'm not joking!)

> This would mean the toolstack either assuming, when someone calls 
> vcpu_set_node_affinity, that soft_affinity == numa_affinity, or keeping 
> its own copy of numa_affinity for each vcpu around somewhere.

> Alternately, we could punt on the NUMA interface altogether for this 
> patch series, and wait until we can implement a full-featured vNUMA 
> interface.  
Well, yes, and let's fall back to that if implementing the above reveals
too difficult or too long, ok?

> That is, for this patch series, make an interface just do 
> NUMA affinity for memory, and "soft" and "hard" affinities for vcpus. 
> Then in another series (perhaps one shortly after that), implement a 
> full vNUMA interface, with vcpus mapped to vNUMA nodes, and vNUMA nodes 
> mapped to pNUMA nodes -- with the toolstack implementing all of this 
> just using the soft affinities.
I agree with everything. About the interactions the evolution of this
series will have with vNUMA, I already talked with Elena in Edinburgh,
and I'll be taking care of those.

Thanks and Regards,

<<This happens because I choose it to happen!>> (Raistlin Majere)
Dario Faggioli, Ph.D, http://about.me/dario.faggioli
Senior Software Engineer, Citrix Systems R&D Ltd., Cambridge (UK)

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