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

[Vijay Kilari <vijay.kilari@xxxxxxxxx>]

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.

>
> Regards,
> Dario
> --
> <<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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