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

[Wei Huang <wei@redhat.com>]

On 10/07/2014 03:58 PM, Paolo Bonzini wrote:
> Il 07/10/2014 21:44, Wei Huang ha scritto:
>> AMD CPU doesn't support hyperthreading. Even though QEMU fixes
>> this issue by setting CPUID_0000_0001_EBX and CPUID_8000_0008_ECX
>> via conversion, it is better to stop end-users in the first place
>> with a warning message.
>
> Hi Wei,
>
> what exactly breaks if you try creating an AMD VM with hyperthreading?
Hi Paolo,

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.

There is a bugzilla reported for such configuration: 
https://bugzilla.redhat.com/show_bug.cgi?id=1135772. So I thought such 
checking might be a good thing to do.
>
> 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. 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"?

>
> Paolo
>