Re: [PATCH 0/3] KVM-userspace: add NUMA support for guests

[Anthony Liguori <anthony@codemonkey.ws>]

Avi Kivity wrote:
> Andre Przywara wrote:
>
>> Any other useful commands for the monitor? Maybe (temporary) VCPU 
>> migration without page migration?
>
> Right now vcpu migration is done externally (we export the thread IDs 
> so management can pin them as it wishes).  If we add numa support, I 
> think it makes sense do it internally as well.  I suggest using the 
> same syntax for the monitor as for the command line; that's simplest 
> to learn and to implement.

I see no compelling reason to do cpu placement internally.  It can be 
done quite effectively externally.

Memory allocation is tough, but I don't think it's out of reach.  
Looking at the numactl man page, you can do:

numactl  --offset=1G  --length=1G --membind=1 --file /dev/shm/A --touch
       Bind the second gigabyte in the tmpfs file /dev/shm/A to node 1.


Since we can already create VM's with the -mem-path argument, if you 
create a 2GB guest and want it to span two numa nodes, you could do:

numactl  --offset=0G  --length=1G --membind=0 --file /dev/shm/A --touch
numactl  --offset=1G  --length=1G --membind=1 --file /dev/shm/A --touch

And then create the VM with:

qemu-system-x86_64 -mem-path /dev/shm/A -mem 2G ...

What's best about this approach, is that you get full access to what 
numactl is capable of.  Interleaving, rebalancing, etc.

Regards,

Anthony Liguori