Thanks you Bhanuprakash for your reply.

I indeed use  vhost-user  interface for OVS-DPDK and vhost-net for standard OVS.
Also saw this article in the link you've sent.
But still try to find out the reasons for the boost performance with OVS-DPDK  
(note that VMs  on both setup are unaware to OVS/OVS-DPDK which is running in 
the host)
Also I found out that the bottleneck are the VMs and not the vswitch running in 
the host. 

These  reasons for  poor performance can be for example:

1. number of packet copies in the path NIC - OVS - OS-guest-virtio - 
Application on guest

2. interrupt upon receiving a packet

3. # of context-switch / VM-exit
etc..

I didn't see any info regarding these potential reasons on the docs.

Best Regards
avi

> -----Original Message-----
> From: Bodireddy, Bhanuprakash [mailto:[email protected]]
> Sent: Wednesday, 24 May, 2017 3:43 PM
> To: Avi Cohen (A); [email protected]
> Subject: RE: OVS vs OVS-DPDK
> 
> >Question:  what are the additional overhead in the standard OVS   that cause
> >to poor performance related to the OVS-DPDK setup ?
> >I'm not talking about  the PMD improvements (OVS-DPDK)  running on the
> >host - but on overhead in the VM context in the standard OVS setup
> 
> When running guest instances on OvS, vhost-net driver modules shall be used.
> In case of OvS-DPDK, vhost-user library is used and runs entirely in user 
> space
> and is the reason for higher performance in VM context Refer to this document
> on some internals of vhost-library:
> http://dpdk.readthedocs.io/en/v16.07/sample_app_ug/vhost.html
> 
> - Bhanuprakash.

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