Re: [Qemu-devel] [PATCH] x86: Allow to set NUMA distance for different NUMA nodes

[Eric Blake]

On 03/10/2017 04:18 AM, He Chen wrote:
> Current, QEMU does not provide a clear command to set vNUMA distance for
> guest although we already have `-numa` command to set vNUMA nodes.
> 

> 
> This patch is going to add SLIT table support in QEMU, and provides
> addtional option `dist` for command `-numa` to allow user set vNUMA

s/addtional/additional/

> distance by QEMU command.
> 
> With this patch, when a user wants to create a guest that contains
> several vNUMA nodes and also wants to set distance among those nodes,
> the QEMU command would like:
> 
> ```
> -object 
> memory-backend-ram,size=1G,prealloc=yes,host-nodes=0,policy=bind,id=node0 \
> -numa node,nodeid=0,cpus=0,memdev=node0 \
> -object 
> memory-backend-ram,size=1G,prealloc=yes,host-nodes=1,policy=bind,id=node1 \
> -numa node,nodeid=1,cpus=1,memdev=node1 \
> -object 
> memory-backend-ram,size=1G,prealloc=yes,host-nodes=2,policy=bind,id=node2 \
> -numa node,nodeid=2,cpus=2,memdev=node2 \
> -object 
> memory-backend-ram,size=1G,prealloc=yes,host-nodes=3,policy=bind,id=node3 \
> -numa node,nodeid=3,cpus=3,memdev=node3 \
> -numa dist,a=0,b=1,val=21 \
> -numa dist,a=0,b=2,val=31 \
> -numa dist,a=0,b=3,val=41 \
> -numa dist,a=1,b=0,val=21 \
> ...
> ```


> +++ b/qapi-schema.json
> @@ -5647,7 +5647,7 @@
>  # Since: 2.1
>  ##
>  { 'enum': 'NumaOptionsType',
> -  'data': [ 'node' ] }
> +  'data': [ 'node', 'dist' ] }

Missing documentation, including the fact that 'dist' is added in 2.10
(you've missed 2.9).

>  
>  ##
> +# @NumaDistOptions:
> +#
> +# Set distance between 2 NUMA nodes. (for OptsVisitor)
> +#
> +# @a: first NUMA node.
> +#
> +# @b: second NUMA node.
> +#
> +# @val: NUMA distance between 2 given NUMA nodes.
> +#
> +# Since: 2.9

This is a new feature, but you've missed soft freeze; this will have to
be 2.10.

> +##
> +{ 'struct': 'NumaDistOptions',
> +  'data': {
> +   'a':   'uint8',
> +   'b':   'uint8',
> +   'val': 'uint8' }}

Using uint8 limits us to at most 256 numa nodes. Is that going to bite
us in the future?

Is 'a' and 'b' really the best naming convention to use (it's concise,
but maybe 'first' and 'second', or 'source' and 'destination' is better)?

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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