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Re: [Qemu-ppc] [Qemu-devel] [PATCH 7/7] numa: Allow empty nodes

From: Eduardo Habkost
Subject: Re: [Qemu-ppc] [Qemu-devel] [PATCH 7/7] numa: Allow empty nodes
Date: Mon, 16 Jun 2014 17:31:24 -0300
User-agent: Mutt/1.5.23 (2014-03-12)

On Mon, Jun 16, 2014 at 05:11:40PM -0300, Eduardo Habkost wrote:
> Wait, is the node ID visible to the guest at all? I believe it is a
> QEMU-internal thing, just to allow the NUMA nodes to be ordered in the
> command-line. I would even claim that the parameter is useless and
> shouldn't have been introduced in the first place.
> What I don't se is: why you need the command-line to look like:
>   -numa node,id=1,mem=X
> when you can simply write it as:
>   -numa node,id=0 -numa node,id=1,mem=X

Oh, I believe now I see it: the problem is not that you don't just need
"memory-less nodes" (which could be simply defined explicitly like
above), but that you need non-contiguous node IDs, which are visible to
the guest.

In this case, my example above with two -numa options would work, but it
would be confusing as the user just wants one node with ID=1 (instead of
two nodes).

So, now your patch makes sense to me. But we first need something to
make sure the following command-line:
  -numa node,id=3 -numa node,id=2
be different from:
  -numa node,id=0 -numa node,id=1 -numa node,id=2 -numa node,id=3

The former should divide the memory in half, between nodes 1 and 2. The
latter should divide the memory in four, between nodes 0, 1, and 2.


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