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

[Dario Faggioli <dario.faggioli@xxxxxxxxxx>]

On Mon, 2016-11-28 at 16:32 +0530, Vijay Kilari wrote:
> On Mon, Nov 28, 2016 at 2:21 AM, Dario Faggioli
> <dario.faggioli@xxxxxxxxxx> wrote:
> > 
> > That makes perfect sense to me, and FWIW, is also what I'd do. In
> > fact,
> > the whole point of what I was saying was not to confuse Xen NUMA
> > support and Dom0 NUMA support; if we want to do both of them, the
> > latter right after the former, fine, but they're separate things
> > indeed.
>   Yes, agreed. Whatever the existing Xen NUMA-Aware code is
> completely kept
> under x86, which can be used for arm as well. So needs cleanup and
> make common
> for both archs.
> 
Sure.

>   Regarding Dom0 NUMA-aware, in arm Dom0 is completely not NUMA-
> aware, not even
> to the extent supported in x86.
> 
Well, Dom0 is ~0% NUMA aware on x86. But it's not important whose Dom0
is _less_ NUMA aware. What I (and also Julien, AFAICT) am talking about
is that we should start make Xen NUMA aware for ARM, before looking at
Dom0.

> > This means that, by default, Dom0 memory is indeed spread among
> > various
> > existing nodes. Eg., on my NUMA test box here at home, here's how
> > things are for Dom0:
> 
> This default behaviour of spreading memory across existing nodes is
> better to some
> extent compared to ARM.. On ARM, All the allocation is based on
> allocator.
> All it assumes all the memory is on single node.
> 
Again, I don't know much about ARM, but my point is this: look at the
differences between xen/include/asm-arm/numa.h and
xen/include/asm-x86/numa.h.

E.g., from the ARM one:

#define cpu_to_node(cpu) 0

This is what I'm saying we should deal with first.

> > dom0_nodes=x is a way to tell Xen to (try as hard as it can) to
> > only
> > allocate the memory for dom0 only from NUMA node x but, even if
> > more
> > than one node is specified, that does not include giving to him a
> > virtual NUMA topology, nor making it aware of the underline NUMA
> > topology of the host in any way.
> > 
> 
>    AFAIK, dom0_nodes is implemented only in x86 not in arm.
> 
Well --given, for instance, the example above-- of course it is! :-)

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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