Re: [Xen-users] Why HVM?

Pasi Kärkkäinen
Sat, 04 Sep 2010 12:14:35 -0000

On Tue, Aug 31, 2010 at 10:40:28AM +0200, Frédéric VANNIÈRE
wrote:
> Hello,
>
> Le 27 août 2010 à 08:41, Jonathan Tripathy a écrit :
> > I''ve noticed some VPS hosting companies offering a Xen
"HVM" option. What are the advantages of a Linux HVM VPS over a PV
one?
>
> I''m working for a hosting company and seriously considering
switching to HVM instead of PV.
>
> We are using PV x86_64 linux guests for several years (100+ VMs) and
I''ve just discovered that PV guest where very bad on some benchmarks
involving many process creation (unixbench).
>
> The Host : Xeon L5530 (HT disabled) , 24 GB mémory
> The guest : 4 vCPUS, 20 GB memory.
>
> Unixbench  :     host = 4000,       PV guest = 1500,        HVM guest =
3900
>
>
> With modern CPUs (Xeon 5500 and 5600 here) and new PV drivers on the guest
(Linux 2.6.36)  HVM gives very low overhead and the performances of HVM guests
are very closed to PV guests.
>

Yeah, 64bit PV guests have some overhead, and HVM might be faster there (when
using PV-on-HVM drivers).
32bit PV guests are fast thought.

-- Pasi