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. Regards, Dennis