Xen users - Jul 2007 - differences between Para-Virtualization and Full-Virtualization?

Hi,

Could someone explain me the following questions:

Where are differences between Para-Virtualization and Full-Virtualization in the
aspects of memory management, CPU and Device I/O, Network?

How is the performance difference between them?

Thanks
Songtao
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Songtao Liu wrote:
> Hi,
>
> Could someone explain me the following questions:
>
> Where are differences between Para-Virtualization and Full-Virtualization
in the aspects of memory management, CPU and Device I/O, Network?
>
> How is the performance difference between them?
>
> Thanks
> Songtao
There are dozens of good documents on this. Boiled down to a few lines, 
full virtualization emulates the entire hardware platform of a guest 
computer. That can be effective for running an otherwise incompatible 
operating sytem, like Windows on a Linux server.

Para-virtualization uses a customized kernel, compatible with the
host''s
kernel and "hypervisor", that speaks compatibly and much more directly
to your host''s hardware. It''s much lighter weight, allows
memory to be
re-allocated among guest domains so a server can run far more guest 
domains,, and provides a really noticeable to any guest operation that 
has to talk to the disk. But it requires a compatible kernel on the 
guest OS, compatible with the Xen version of the host OS.

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> > Hi,
> >
> > Could someone explain me the following questions:
> >
> > Where are differences between Para-Virtualization and
> Full-Virtualization in the aspects of memory management, CPU and
> Device I/O, Network?
> >
> > How is the performance difference between them?
> >
> > Thanks
> > Songtao
> There are dozens of good documents on this. Boiled down to a few
> lines, 
> full virtualization emulates the entire hardware platform of a guest 
> computer. That can be effective for running an otherwise incompatible
> 
> operating sytem, like Windows on a Linux server.
> 
> Para-virtualization uses a customized kernel, compatible with the
> host''s 
> kernel and "hypervisor", that speaks compatibly and much more
> directly 
> to your host''s hardware. It''s much lighter weight, allows
memory to
> be 
> re-allocated among guest domains so a server can run far more guest 
> domains,, and provides a really noticeable to any guest operation
> that 
> has to talk to the disk. But it requires a compatible kernel on the 
> guest OS, compatible with the Xen version of the host OS.
How would one go about compiling his own compatible kernel on the guest
OS? What needs to be done to the kernel.

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thewird wrote:
> How would one go about compiling his own compatible kernel on the 
> guest OS? What needs to be done to the kernel.
Ooff. It''s like fixing your own brakes Not too painful if
you''ve gotten
some practice, but I don''t recommend it as a first step, because a 
mistake can be nasty indeed.

You''re probably much safer using one built by people comfortable with 
it, such as the CentOS/RHEL operating systems with Xen kernels built in, 
or the Debian Xen packages, and then reviewing their source packages to 
see what the packages and patches involved are. There are patches needed 
on top of the standard Linux or Solaris or BSD kernels.

There is some documentation in the Xen software tarballs, at 
Sourceforge.net and www.xensource.com.

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Hello,

	I think it is true what Nico writes, but I would say - from the
philosophical point of view of me the main difference between full
virtualization and paratirtualization is in the fact, the fully virtualized
OS "does not know" it runs on some emulation of the computer and there
can
be some other OS instances with which the resources can be shared, but
paravirtualized can. It means, in paravirtauliyation can be also changed the
disks, CPUs, memory etc. During the run of the system and the guest OS can
handle this changes correctly. 
	The consequence is then, the paravirtualized system can generally
know more about the system where it runs because it can cooperate with the
hypervisor.
	I do not think it is an exact information there must be some kernel
etc. with some special properties - there exist also paravirtualization
drivers for windows to cooperate with the hyparvisor - and windows have no
kernel in the linux meaning...

	With best regards

		Archie

-----Original Message-----
From: xen-users-bounces@lists.xensource.com
[mailto:xen-users-bounces@lists.xensource.com] On Behalf Of thewird
Sent: Friday, July 20, 2007 10:55 AM
To: Nico Kadel-Garcia
Cc: xen-users@lists.xensource.com
Subject: Re: [Xen-users] differences between Para-Virtualization
andFull-Virtualization?
> > Hi,
> >
> > Could someone explain me the following questions:
> >
> > Where are differences between Para-Virtualization and
> Full-Virtualization in the aspects of memory management, CPU and
> Device I/O, Network?
> >
> > How is the performance difference between them?
> >
> > Thanks
> > Songtao
> There are dozens of good documents on this. Boiled down to a few
> lines, 
> full virtualization emulates the entire hardware platform of a guest 
> computer. That can be effective for running an otherwise incompatible
> 
> operating sytem, like Windows on a Linux server.
> 
> Para-virtualization uses a customized kernel, compatible with the
> host''s 
> kernel and "hypervisor", that speaks compatibly and much more
> directly 
> to your host''s hardware. It''s much lighter weight, allows
memory to
> be 
> re-allocated among guest domains so a server can run far more guest 
> domains,, and provides a really noticeable to any guest operation
> that 
> has to talk to the disk. But it requires a compatible kernel on the 
> guest OS, compatible with the Xen version of the host OS.
How would one go about compiling his own compatible kernel on the guest
OS? What needs to be done to the kernel.

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