Xen users - Sep 2012 - Running Linux VM in para mode with Intel VT enabled

Hi all,
        I am having a server running XEN,with ubuntu 12.04 as Domain 0.

Intel VT is turned on by default and i dont want to run any Windows OS as
VM.In that case

1. how can i makesure that all the created VM will be in
paravirtualized mode even with VT enabled?

I have heard that in Full Virtualization hypervisor needs to work hard for
emulating all the underlying hardware,which may reduce performance for too
much i/o specific applications when compared to para mode.

*2.Can i be able to run Linux VM in para mode with VT enabled?

3.Will simply turning on VT support changes virtualization type from
para to full for all vms created on that machine?

4.Will there be any performance improvement for VM running Linux OS if
VT is enabled?*

*5.Is it normal to miss vmx flag in /proc/cpuinfo after booting to XEN
kernel,even with VT enabled?*


*Regards,*

*Kevin*


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On Thu, Sep 20, 2012 at 10:34 PM, kevin parker
<kevin.parker092@gmail.com> wrote:
> 1. how can i makesure that all the created VM will be in
> paravirtualized mode even with VT enabled?
Depends on how you create the VMs.

For example, if you create it by hand, then if you DON''T have a line
"builder=''hvm''" in the VM config file, then
you''re using PV. If you
use some kind of frontend (e.g. libvirt) it should have an option to
choose VM type.
> 2.Can i be able to run Linux VM in para mode with VT enabled?
yes
> 3.Will simply turning on VT support changes virtualization type from para
to
> full for all vms created on that machine?
no
> 4.Will there be any performance improvement for VM running Linux OS if VT
is
> enabled?
no
> 5.Is it normal to miss vmx flag in /proc/cpuinfo after booting to XEN
> kernel,even with VT enabled?
yes. Xen intentionally hides it because xen uses it, and no other
process in the dom0 can use it anyway.

-- 
Fajar

>________________________________
> From: kevin parker <kevin.parker092@gmail.com>
>To: xen-users@lists.xen.org 
>Sent: Thursday, September 20, 2012 8:34 AM
>Subject: [Xen-users] Running Linux VM in para mode with Intel VT enabled
> 
>
>Hi all,
>        I am having a server running XEN,with ubuntu 12.04 as Domain 0.
>Intel VT is turned on by default and i dont want to run any Windows OS as
VM.In that case
>1. how can i makesure that all the created VM will be in
paravirtualized mode even with VT enabled? 
>I have heard that in Full Virtualization hypervisor needs to work hard for
emulating all the underlying hardware,which may reduce performance for too much
i/o specific applications when compared to para mode.
The difference between running a guest vm as a PV vs. as a HVM is controlled by
the guest vm''s configuration.   In particular, if your guest
vm''s configuration contains the following lines, then the guest would
be launched as a HVM:

kernel = ''/usr/lib/xen-4.0/boot/hvmloader''
builder=''hvm''
Thus, if you want to ensure that your Ubunto guests runs as a PV you need to
specify something along the following lines:
kernel = ''/boot/vmlinuz-2.6.33.20.x86_64''       # substitute
this with your specific Ubuntu kernel
ramdisk = ''/boot/initrd-2.6.33.20.x86_64''  # substitute this
with your specific Ubuntu ramdisk, if you want to use it, this is optional

extra = ''selinux=0 elevator=noop''  # not strictly necessary,
but allows you to pass parameters during boot to the kernel

For more infos check this out:
http://xenbits.xen.org/docs/unstable/man/xl.cfg.5.html#paravirtualised__pv__guest_specific_options



2.Can i be able to run Linux VM in para mode with VT enabled? 3.Will simply
turning on VT support changes virtualization type from para to full for all vms
created on that machine? 4.Will there be any performance improvement for VM
running Linux OS if VT is enabled?
>5.Is it normal to miss vmx flag in /proc/cpuinfo after booting to XEN
kernel,even with VT enabled?
>
>
>Regards,
>Kevin
>_______________________________________________
>Xen-users mailing list
>Xen-users@lists.xen.org
>http://lists.xen.org/xen-users
>
>
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