Re: [Qemu-devel] [PATCH 2.1 00/28] Current state of NUMA series, and hostmem improvements

[Paolo Bonzini <pbonzini@redhat.com>]

Il 05/03/2014 12:05, Andreas Färber ha scritto:
> Am 04.03.2014 15:00, schrieb Paolo Bonzini:
>> This series includes all the pending work on QOMifying the memory
>> backends.
> [snip]
>
> There's also a recent RFC from Chen Fan about how to model the
> association between NUMA nodes and CPU socket/core/thread that
> would/should influence this series if we're aiming for 2.1 now.

I don't think it should, apart from conflicts.  This series only changes 
things about memory.  CPUs are handled the same before and after the 
patches.

> I didn't review it in-depth yet, but minor technical issues apart, I
> think we need to keep NUMA and CPU separate,

I agree.

> Compare that to:
>
> /machine
>   /node[0] # This is not really telling!
>     /socket[0]
>       /core[0]
>         /thread[0] # So CPUState != thread?
>           cpu -> /machine/unassigned/device[0]
>   /unassigned
>     /device[0]

I think this is better; in our world we can have multiple sockets in the 
same NUMA node.  But CPUState == thread, so you can have just /thread[0] 
-> /machine/unassigned/device[0].

Alternatively, and to keep CPU + NUMA even *more* separate:

   /machine
     /node[0]
        /cpu[0] -> /machine/unassigned/device[0]
        ...
     /socket[0]
        /core[0]
           /thread[0] -> /machine/unassigned/device[0]
     /unassigned
        /device[0]

> which then brings up the
> question Chen Fan asked about whether we need to support splitting CPU
> threads of one core or CPU cores of one socket onto different NUMA
> nodes. If we can stop supporting this, 2.0 would be a good point in time
> to catch this with an error message at least, even if the remodeling
> depending on it happens post-2.0.

> Note that according to my interpretation of QOM ABI stability rules we
> can't just turn a link<cpu> into a child<cpu> without renaming, thus
> trying to be forward-looking for where we want to go design-wise.

I think we can.  Children and links look exactly the same from the outside.

Paolo