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

On 11/05/2013 03:39 PM, George Dunlap wrote:
On 11/05/2013 03:23 PM, Jan Beulich wrote:
On 05.11.13 at 16:11, George Dunlap <george.dunlap@xxxxxxxxxxxxx>
Or, we could internally change the names to "cpu_hard_affinity" and
"cpu_soft_affinity", since that's effectively what the scheduler will
do.  It's possible someone might want to set soft affinities for some
other reason besides NUMA performance.

I like that.

A potential problem with that is the "auto domain numa" thing.  In this
patch, if the domain numa affinity is not set but vcpu numa affinity is,
the domain numa affinity (which will be used to allocate memory for the
domain) will be set based on the vcpu numa affinity.  That seems like a
useful feature (though perhaps it's starting to violate the "policy
should be in the tools" principle).  If we change this to just "hard
affinity" and "soft affinity", we'll lose the natural logical connection
there.  It might have impacts on how we end up doing vNUMA as well.  So
I'm a bit torn ATM.

Dario, any thoughts?

[Coming back after going through the whole series]

This is basically the main architectural question that needs to be sorted out with the series: Do we bake in that the "soft affinity" is specifically for NUMA-ness, or not?

The patch the way it is does make this connection, and that has several implications: * There is no more concept of a separate "domain numa affinity" (Patch 06); the domain numa affinity is just a pre-calculated union of the vcpu affinities. * The interface to this "soft affinity" is a bitmask of numa nodes, not a bitmask of cpus.

If we're OK with that direction, then I think this patch series looks pretty good.

Release-wise, I think as long as we're OK with libxl providing a "set_vcpu_numa_affinity", then we can always come back and change the implementation later if we want to maintain that distinction internally.


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