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

[Dario Faggioli <dario.faggioli@xxxxxxxxxx>]

On Sat, 2016-11-26 at 12:29 +0530, Vijay Kilari wrote:
> 4) Generating memory nodes for DOM0
> ---------------------------------------------------------
> Linux kernel device drivers that uses devm_zalloc(), tries to
> allocate memory
> from local memory node. So Dom0 needs to have memory allocated on all
> the
> available nodes of the system.
> 
So, first of all, I know next to nothing about ARM, NUMA or non-NUMA.

That being said, providing a guest with a NUMA layout is what we call
"virtual NUMA" (vNUMA). It is implemented (although it still has some
issues) for x86 already (so you can have a look), but only for DomU.

I agree that we need to support vNUMA for Dom0 sooner rather than
later, and I agree that Dom0 is a bit special, so some tricks may be
necessary. But until we don't implement vNUMA for Dom0, Dom0 is just a
non-NUMA virtual machine, and the kernel running inside that should
just behave like it behaves on a non-NUMA box.

Again, I don't know much about ARM, but I think that, until we don't
have vNUMA for Dom0, that devm_zalloc() thing will just see 1 and only
1 NUMA node from which to allocate memory.

That being said, and for what it's worth...

> Ex: SMMU driver of device on node 1 tries to allocate memory
> on node 1.
> 
> ISSUE:
>  - Dom0's memory should be split across all the available memory
> nodes
>    of the system and memory nodes should be generated accordingly.
>
...This is the default behavior, at least on x86.

>  - Memory DT node generated by Xen for Dom0 should populate numa-
> node-id
>    information.
> 
Generating DT nodes for Dom0 is exactly what I mean when I say
"implementing / enabling vNUMA for Dom0" (in this case on ARM).

So, yes, let's do it, but let's discuss how to do it properly (e.g., if
there's anything that can be common between archs, such as some bits of
the interface).

Thanks and 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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