Re: [Hackathon minutes] PV frontends/backends and NUMA machines

[Tim Deegan <tim@xen.org>]

At 09:47 +0100 on 21 May (1369129629), George Dunlap wrote:
> On Tue, May 21, 2013 at 9:32 AM, Tim Deegan <tim@xen.org> wrote:
> > At 14:48 +0100 on 20 May (1369061330), George Dunlap wrote:
> >> So the work items I remember are as follows:
> >> 1. Implement NUMA affinity for vcpus
> >> 2. Implement Guest NUMA support for PV guests
> >> 3. Teach Xen how to make a sensible NUMA allocation layout for dom0
> >
> > Does Xen need to do this?  Or could dom0 sort that out for itself after
> > boot?
> 
> There are two aspects of this.  First would be, if dom0.nvcpus <
> host.npcpus, to place the vcpus reasonably on the various numa nodes.

Well, that part at least seems like it can be managed quite nicely from
dom0 userspace, in a Xen init script.  But...

> The second is to make the pfn -> NUMA node layout reasonable.  At the
> moment, as I understand it, pfns will be striped across nodes.  In
> theory dom0 could deal with this, but it seems like in practice it's
> going to be nasty trying to sort that stuff out.  It would be much
> better, if you have (say) 4 nodes and 4GiB of memory assigned to dom0,
> to have pfn 0-1G on node 0, 1-2G on node 2, &c.

Yeah, I can see that fixing that post-hoc would be a PITA.  I guess if
you figure out the vcpu assignments at dom0-build time, the normal NUMA
memory allocation code will just DTRT (since that's what you'd want for
a comparable domU)?

Tim.