libvirt users - Jul 2017 - Re: Question about disabling '3dnowprefetch' CPU feature in Xen Guest using libvirt

Dear All,

    I'm reaching this mail-list to ask a small question about disabling
'3dnowprefetch' CPU feature in Xen Guest using libvirt.

    This is my environment:
    Fedora release 26 (Twenty Six)
    4.11.0-0.rc3.git0.2.fc26.x86_64
    xen-4.8.1-2.fc26.x86_64
    libvirt-3.2.1-1.fc26.x86_64

    I can disable '3dnowprefetch' CPU feature in guest via 'xl'
command,
with adding `cpuid='host,3dnowprefetch=0'` into the CFG file.

    However, follow the instruction (https://libvirt.org/
formatdomain.html#elementsCPU), I added the following block into my XML
file:

```
  <cpu mode='host-passthrough' check='none'>
    <feature policy='disable' name='3dnowprefetch'/>
  </cpu>
```

    Created the instance, seemed this feature was not being disabled in my
guest. (I was able to see '3dnowprefetch' in `lscpu` outputs)

    Anybody has idea on this? Does libvirt support this for Xen?

    Any help would be appreciated. Thank you in advance.

Regards,
Charles


Charles Shih (史晨)
Quality Engineer
Red Hat, Platform QE, Virt QE, Section 1
Email: cheshi@redhat.com
IRC: cheshi @ #eng-china, #hyperv ,#qa, #virt
T: +86 10 65627484 <010%206562%207484>  - IP: 8387484
M: +86 18611268098 <186%201126%208098>

On 06/18/2017 09:01 PM, Charles Shih wrote:
> Dear All,
> 
>      I'm reaching this mail-list to ask a small question about
disabling
> '3dnowprefetch' CPU feature in Xen Guest using libvirt.
> 
>      This is my environment:
>      Fedora release 26 (Twenty Six)
>      4.11.0-0.rc3.git0.2.fc26.x86_64
>      xen-4.8.1-2.fc26.x86_64
>      libvirt-3.2.1-1.fc26.x86_64
> 
>      I can disable '3dnowprefetch' CPU feature in guest via
'xl' command, with
> adding `cpuid='host,3dnowprefetch=0'` into the CFG file.
> 
>      However, follow the instruction 
> (https://libvirt.org/formatdomain.html#elementsCPU 
> <https://libvirt.org/formatdomain.html#elementsCPU>), I added the
following
> block into my XML file:
> 
> ```
>    <cpu mode='host-passthrough' check='none'>
>      <feature policy='disable' name='3dnowprefetch'/>
>    </cpu>
> ```
> 
>      Created the instance, seemed this feature was not being disabled in my
> guest. (I was able to see '3dnowprefetch' in `lscpu` outputs)
> 
>      Anybody has idea on this? Does libvirt support this for Xen?
Currently, the libvirt libxl driver only supports VMX or SVM CPU feature, and 
for that you'd need libvirt 3.3.0

http://libvirt.org/git/?p=libvirt.git;a=commit;h=c268b9eaeb4321ef311ae2e152b80752918eb289

More support for CPU customization is on the todo list. Contributions are always
warmly welcomed :-).

Regards,
Jim

Hi Jim,

  Thank you for the great support and expertise. It helps so much! :-)

Regards,
Charles

Charles Shih (史晨)
Quality Engineer
Red Hat, Platform QE, Virt QE, Section 1
Email: cheshi@redhat.com
IRC: cheshi @ #eng-china, #hyperv ,#qa, #virt
T: +86 10 65627484  - IP: 8387484
M: +86 18611268098


On Wed, Jul 5, 2017 at 11:42 PM, Jim Fehlig <jfehlig@suse.com> wrote:
> On 06/18/2017 09:01 PM, Charles Shih wrote:
>
>> Dear All,
>>
>>      I'm reaching this mail-list to ask a small question about
disabling
>> '3dnowprefetch' CPU feature in Xen Guest using libvirt.
>>
>>      This is my environment:
>>      Fedora release 26 (Twenty Six)
>>      4.11.0-0.rc3.git0.2.fc26.x86_64
>>      xen-4.8.1-2.fc26.x86_64
>>      libvirt-3.2.1-1.fc26.x86_64
>>
>>      I can disable '3dnowprefetch' CPU feature in guest via
'xl' command,
>> with adding `cpuid='host,3dnowprefetch=0'` into the CFG file.
>>
>>      However, follow the instruction (https://libvirt.org/formatdom
>> ain.html#elementsCPU
<https://libvirt.org/formatdomain.html#elementsCPU>),
>> I added the following block into my XML file:
>>
>> ```
>>    <cpu mode='host-passthrough' check='none'>
>>      <feature policy='disable'
name='3dnowprefetch'/>
>>    </cpu>
>> ```
>>
>>      Created the instance, seemed this feature was not being disabled
in
>> my guest. (I was able to see '3dnowprefetch' in `lscpu`
outputs)
>>
>>      Anybody has idea on this? Does libvirt support this for Xen?
>>
>
> Currently, the libvirt libxl driver only supports VMX or SVM CPU feature,
> and for that you'd need libvirt 3.3.0
>
> http://libvirt.org/git/?p=libvirt.git;a=commit;h=c268b9eaeb4
> 321ef311ae2e152b80752918eb289
>
> More support for CPU customization is on the todo list. Contributions are
> always warmly welcomed :-).
>
> Regards,
> Jim
>