[CentOS-virt] performance differences between kvm/xen

Tue Oct 19 12:32:54 UTC 2010
Dennis Jacobfeuerborn <dennisml at conversis.de>

On 10/19/2010 01:16 PM, Jerry Franz wrote:
>    On 10/19/2010 03:47 AM, Dennis Jacobfeuerborn wrote:
>> On 10/19/2010 09:41 AM, Pasi Kärkkäinen wrote:
>>> 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.
> There appear to be some interactions with the Intel VT-d processor features.
> http://www.xen.org/files/xensummit_intel09/xensummit2009_IOVirtPerf.pdf
> If I understand that paper correctly, HVM+VT-d outperforms PV by quite a
> lot (if you have VT-d support on your system).

Thanks for that link. Just to make my criticism of the initial claim more 
clear: I don't claim that HVM can never be faster than PV but that you need 
to understand when exactly this is the case. For example I'm not sure that 
x86_64 vs. x86 really enters into this but I can definitely see VT-d making 
an impact there.