Re: [Xen-users] Running Linux VM in para mode with Intel VT enabled

[Matthias Blankenhaus <matthiasblankenhaus@xxxxxxxxx>]

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From: kevin parker <kevin.parker092@xxxxxxxxx>
To: xen-users@xxxxxxxxxxxxx
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

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