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Re: [Xen-users] Why HVM?

To: Frédéric VANNIÈRE <frederic@xxxxxxxxxxx>
Subject: Re: [Xen-users] Why HVM?
From: Pasi Kärkkäinen <pasik@xxxxxx>
Date: Sat, 4 Sep 2010 15:14:35 +0300
Cc: Xen Users <Xen-users@xxxxxxxxxxxxxxxxxxx>, Jonathan Tripathy <jonnyt@xxxxxxxxxxx>
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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

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