Re: [Qemu-devel] [PATCH 1/1] target-i386: prevent users from setting threads>1 for AMD CPUs

[Wei Huang]

On 10/07/2014 04:36 PM, Paolo Bonzini wrote:
> Il 07/10/2014 23:16, Wei Huang ha scritto:
> > It isn't a bug IMO. I tested various combinations; and current QEMU
> > handles it very well. It converts threads=n to proper
> > CPUID_0000_0001_EBX[LogicalProcCount] and CPUID_8000_0008_ECX[NC]
> > accordingly for AMD.
>
> So if it ain't broken, don't fix it. :)
>
> > > I am worried that the default CPU is an AMD one when KVM is disabled,
> > > and thus "qemu-system-x86_64 -smp threads=2" will likely be broken.
> >
> > "-smp threads=2" will be rejected by the patch.
>
> Yeah, I am afraid that is an incompatible change, and one more reason
> not to do this.  AMD not selling hyperthreaded processors does not mean
> that they could not be represented properly with the CPUID leaves that
> AMD processors support.
I am OK with either way. The key question is: should QEMU presents 
CPUIDs strictly as specified by the command line or QEMU can tweak a 
little bit on behalf of end-users? For instance, if end-users say "-smp 
8,cores=2,threads=2,sockets=2", they meant "two socket, each has two 
2-hyperthread cores". Current QEMU will convert CPUID as "two socket, 
each has 4 cores". My patch will forbid the tweaking...

-Wei

> Paolo
>
> > Unless the meaning of
> > threads is not limited to threads-per-core, shouldn't end users use
> > "-smp 2" in this case or something like "-smp 2,cores=2,sockets=1"?