[Xen-users] Re: Basic Xen Questions

[Ritesh Raj Sarraf <rrs@xxxxxxxxxxxxxx>]

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Randy Thelen on Monday 20 Mar 2006 12:45 wrote:

> Ritesh Raj Sarraf wrote:
> 
>> 1) If I patch my kernel with Xen, will I be compromising on any of
>> the other
>> features that I've patched ? (Namely UML and swsusp. I use UML a lot)
> 
> swsusp:  Software Suspend
> http://sourceforge.net/projects/swsusp
> 
> It's unlikely this will work with Xen.  This would undoubtedly
> require a patch into the Xen hypervisor to save & restore the other
> domains.  Even if you were only running dom0, this might still not work.
> 
> UML: User Mode Linux
> Interesting.  UML is a technology which accomplishes some of the same
> goals as Xen.  Xen can run multiple instances of Linux, like UML.  So
> from that stand point, you'll get many of the same features as UML.
> However, Xen can also run other operating systems: FreeBSD, NetBSD,
> Minix (in theory), Windows XP (with the right processor), etc.
>

Thanks for replying.

Basically I'm looking to build the kernel with all support.
I want a kernel with Xen support which I can use for UML too when I'm not
running any other domU (other OSes in Xen) want.
Right now my kernels are patched with UML but I don't use UML always. I use
it only when I want, else my machine runs as a normal machine.

> It's my opinion that Xen is a superset of the functionality one can
> get with UML.  If UML is important to you, I encourage you to
> continue learning about the virtues of Xen.
> 
> The answer to the question: "will I be compromising on any of the
> other features?" is yes.
> 
>> 2) So when I boot with a Xen kernel, the OS it boots into is dom0
>> which
>> simply is my normal OS. Right ?
> 
> More or less.  However, the Linux running as dom0 will likely not be
> the same -kernel- image that you are currently running.  But, it will
> be Linux and it will see your current file systems, devices (assuming
> your configuration files are suitably identical), etc.
>

So basically it'd be the same kernel with Xen features?
 
>> 3) If I'm correct about Question 2 then, "when only using dom0,
>> does it add
>> any virtualization overhead to the host OS i.e. dom0 ? Or does it
>> simply
>> function as a normal Linux Kernel with Xen features not being in
>> use ? "
> 
> It does add overhead to use Xen even with only dom0 present, but
> they're minimal.  It's likely you won't notice them.  Various
> presentations indicate the performance impact is as low as 3%.
> 
> -- Randy

That's good. 3% overhead is worth trying Xen.
:-)

Thanks,
Ritesh
- -- 
Ritesh Raj Sarraf
RESEARCHUT -- http://www.researchut.com
"Necessity is the mother of invention."
"Stealing logic from one person is plagiarism, stealing from many is
research."
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