[CentOS-virt] performance differences between kvm/xen

On Tue, Oct 19, 2010 at 12:47:03PM +0200, Dennis Jacobfeuerborn wrote:
> On 10/19/2010 09:41 AM, Pasi Kärkkäinen wrote:
> > On Sat, Oct 16, 2010 at 09:58:15PM +0200, Dennis Jacobfeuerborn wrote:
> >> On 10/16/2010 08:11 PM, Pasi Kärkkäinen wrote:
> >>> On Thu, Oct 14, 2010 at 02:16:42PM +0100, Bart Swedrowski wrote:
> >>>> Hi Karanbir,
> >>>>
> >>>> On 14 October 2010 19:59, Karanbir Singh<mail-lists at karan.org>   wrote:
> >>>>>
> >>>>> On 10/14/2010 07:48 AM, Tom Bishop wrote:
> >>>>>> I think xen is still on top in terms of performance and features....now
> >>>>>
> >>>>> that is indeed what it 'feels' like, but I'm quite keen on putting some
> >>>>> numbers on that.
> >>>>
> >>>> I have done some testing some time ago on one of the EQ machines that
> >>>> I got from hetzner.de.  Full spec of the machine was as following:
> >>>>
> >>>>     * Intel® Core??? i7-920
> >>>>     * 8 GB DDR3 RAM
> >>>>     * 2 x 750 GB SATA-II HDD
> >>>>
> >>>> It's nothing big but even though results are quite interesting.  All
> >>>> tests were performed on CentOS 5.5 x86_64 with PostgreSQL 8.4 (from
> >>>> CentOS repos).
> >>>>
> >>>
> >>> Note that 64bit Xen guests should be HVM, not PV, for best performance.
> >>> Xen HVM guests obviously still need to have PV-on-HVM drivers installed.
> >>>
> >>> 32bit Xen guests can be PV.
> >>
> >> Hm, why would HVM be faster than PV for 64 bit guests?
> >>
> >
> > It's because of the x86_64 architecture, afaik.
> >
> > There was some good technical explananation about it,
> > but I can't remember the url now.
> 
> In that case I'll have to call this advice extremely bogus and you probably 
> should refrain from passing it on. The only way I can see this being true 
> is some weird corner case.
> 

It's not bogus, you can go ask on xen-devel :)

-- Pasi