[CentOS-virt] performance differences between kvm/xen

Dennis Jacobfeuerborn dennisml at conversis.de
Wed Oct 20 07:35:14 EDT 2010

On 10/20/2010 08:12 AM, Grant McWilliams wrote:
>      > 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
> Even though this is Intel talking I'd still be very sceptical of getting
> those numbers since this is quite the opposite of what I've seen.
> Maybe the vt-d is getting good enough to actually accelerate IO operations
> but even so that would only happen on the latest hardware.
> I will say that Xen has a really long packet path though.

Being skeptical is the best approach in the absence of 
verifiable/falsifiable data. Today or tomorrow I'll get my hands on a new 
host system and although it is supposed to go into production immediately I 
will probably find some time to do some rudimentary benchmarking in that 
regard to see if this is worth investigating further. Right now I'm 
planning to use fio for block device measurements but don't know any decent 
(and uncomplicated) network i/o benchmarking tools. Any ideas what tools I 
could use to quickly get some useful data on this from the machine?


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