Re: [Xen-devel] arm64: Approach for DT based NUMA and issues

[Julien Grall <julien.grall@xxxxxxx>]

Hello Vijay,

On 02/03/17 12:39, Vijay Kilari wrote:
> On Fri, Dec 16, 2016 at 3:48 PM, Dario Faggioli
> <dario.faggioli@xxxxxxxxxx> wrote:
> > On Fri, 2016-12-16 at 09:40 +0000, Julien Grall wrote:
> > > Hi Vijay,
> > > On 16/12/2016 07:39, Vijay Kilari wrote:
> > > > If we drop numa-node-id from memory node generated to dom0, then
> > > > dom0 will
> > > > assume all the memory is from node0. So eventually node1 device
> > > > intialization fails.
> > > I suggested to drop the property numa-node-id from every node (not
> > > only
> > > memory one). So DOM0 will think it is running a non-NUMA platform.
> > >
> > >  From my knowledge this is working on x86, and I don't understand
> > > why
> > > this would be an issue on ARM. If you think the device may not work,
> > > please explain why.
> > Yes, I confirm that what you said works and any x86 NUMA system I've
> > seen.
> >
> > AFAIUI, since Vijay is talking about "devices", the x86 equivalent of
> > what would be an "IONUMA system", i.e. a platform where I/O devices are
> > physically attached to more than just one I/O hub, which in turn are
> > attached to different nodes.
> > I don't have first hand experience with these systems on the x86 world,
> > but I'm quite sure they also function with the configuration Julien is
> > suggesting to use.
> >
> > Boris did some work to _improve_ the situation (namely, to make it
> > possible for *Xen* to report to the toolstack, to which NUMA node a
> > specific device is attached to). But:
> >  - things were working already before this
> >  - that does involve Xen and toolstack, while Dom0 remains totally
> >    NUMA _unaware_.
> >
> > And I indeed think that doing what Julien says (i.e., keep dom0 NUMA-
> > ignorant) is, if possible, best as a first step.
>
> Sorry for late reply. I want to confirm only after checking if this
> approach works.
>
> Yes for first step implementation this fine.
> For now, our platform does not have any such restrictions that memory
> for IO device
> should be always local.
> Also, the issue is seen with SMMU, which is going to be hidden from Dom0.
> I have mentioned this restriction in my NUMA RFC patch commit.
Can you detail the restrictions with SMMU? Which memory should be 
allocated to the correct node? Stage-2 page tables?
Regards,

--
Julien Grall

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