Re: [Qemu-devel] [RFC] allow multi-core guests: introduce cores= option to -cpu

[Andre Przywara]

Samuel Thibault wrote:
> Andre Przywara, le Fri 03 Jul 2009 16:41:56 +0200, a écrit :
> > -smp 16 -cpu host,cores=8
>
> That means 8 cores with 2 threads each, thus 16 threads?
No, that meant: 16 vCPUs total with 8 cores per physical packages. I 
don't have any notion for threads in the current code, although I agree 
that this should be introduced.
AFAIK Windows XP Home is limited to one socket, where XP Pro can use up 
to two sockets. Using -smp 4 on a XP Pro (64bit) caused an early BSOD 
stating "MULTIPROCESSOR_CONFIGURATION_NOT_SUPPORTED" (because it saw 
four sockets instead of four cores).
I think WindowsXP Home should even be worse (though I don't have an 
image here to test it), because it would not boot any SMP guest.

> Ok, that can be
> later generalized into for instance
>
> -smp 16 -cpu host,nodes=2,sockets=2,cores=2
>
> to define 2 NUMA nodes of 2 sockets of 2 cores, each core thus having 16
> threads.
Well, generalizing is a good idea, but as Brian wrote this shouldn't be 
done in the -cpu option. Putting the NUMA nodes into here seems quite 
logical, but would also requires to
a) describe the NUMA topology separated from this option    or
b) pull all the NUMA topology description into this one.
Maybe one could describe cores, threads, sockets and nodes in -smp and 
declare the memory topology only in -numa.

Regards,
Andre.

--
Andre Przywara
AMD-Operating System Research Center (OSRC), Dresden, Germany
Tel: +49 351 488-3567-12