Re: Networking performance on a KVM Host (with no guests)

[Chegu Vinod <chegu_vinod@xxxxxx>]

On 4/18/2012 10:43 PM, Gleb Natapov wrote:
> On Thu, Apr 19, 2012 at 03:53:39AM +0000, Chegu Vinod wrote:
> > Hello,
> >
> > Perhaps this query was answered in the past. If yes kindly point me to
> > the same.
> >
> > We noticed differences in networking performance (measured via netperf
> > over a 10G  NIC) on an X86_64 server between the following two
> > configurations :
> >
> > 1) Server run as a KVM Host (but with no KVM guests created on it (or) no
> > extra  bridges created other than the default vibr0 bridge)
> >
> > vs.
> >
> > 2) The same server running the same version of Linux but without any of the
> > virtualization software installed on it.
> >
> > Config #2 performed much better !
> > Is this expected ? What are the reasons behind this ?
> >
> > Is there any way to gain back the loss in performance on the KVM host
> > without having to uninstall the virtualization software (i.e. in Config 1).

Just an observation   :

Removing the "intel_iommu=on" boot time parameter  in the Config 1 case 
seemed to help
gain back the networking performance on the KVM host... i.e. performed 
nearly the same as
in Config2.   Didn't have to change any of the VT settings in the BIOS...

Trying to understand why that's the case...   Any pointers ?

Vinod

> --
> 			Gleb.

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