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RE: [Xen-users] xen over quemu OR quemu in Xen domU on a system with HVM-capable CPU


  • To: "Igor Chubin" <igor@xxxxxxx>
  • From: "Petersson, Mats" <Mats.Petersson@xxxxxxx>
  • Date: Wed, 30 May 2007 18:41:21 +0200
  • Cc: xen-users@xxxxxxxxxxxxxxxxxxx
  • Delivery-date: Wed, 30 May 2007 09:40:19 -0700
  • List-id: Xen user discussion <xen-users.lists.xensource.com>
  • Thread-index: Acei1+mDC8pHkJLaSPagPtiLMiNrjgAABYbQ
  • Thread-topic: [Xen-users] xen over quemu OR quemu in Xen domU on a system with HVM-capable CPU

 

> -----Original Message-----
> From: Igor Chubin [mailto:igor@xxxxxxx] 
> Sent: 30 May 2007 17:34
> To: Petersson, Mats
> Cc: Igor Chubin; xen-users@xxxxxxxxxxxxxxxxxxx
> Subject: Re: [Xen-users] xen over quemu OR quemu in Xen domU 
> on a system with HVM-capable CPU
> 
> ...
> > > Please tell me are there the same restrictions for the 
> > > hvm-capable systems?
> > 
> > If you load Linux (or such) in HVM mode, you can run kqemu 
> inside that
> > Linux. I'm not entirely sure I understand the advantage of this,
> > compared to running the OS you want to run in QEMU inside a 
> HVM virtual
> > machine in the first place, but yes, it's possible. 
> 
> 
> 
> Small addition.
> 
> 
> Mats, I don't want to run linux inside domU to run quemu.
> 
> I want to run quemu and kquemu in Xen domain 0 directly.

Yes, but I still don't understand why, including after your other
explanation about running "as many OS's as possible", this is better
than just running a HVM domain in the first place - HVM domains aren't
VERY resource consuming, and you'll be running a QEMU-DM or full-QEMU
per "guest"[1]. 

The only advantage I can see is that since QEMU itself is using virtual
memory, you could possibly swap a "guest" to disk, which means that you
can overcommit the memory. I'm however sceptical that this is a REAL
advantage over running a virtual machine with swap in the guest - the
swapping within the guest would be much more selective on what gets
swapped out, compared to swapping out some "random" bits of the
"qemu+data" images. 

[1] Here I use the term guest in a looser meaning than I normally would
do, e.g. a QEMU instance would also count as a guest.  

--
Mats
> 
> -- 
> WBR, i.m.chubin
> 
> 
> 
> 



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