Subject: Re: Low throughput in VMs using VxLAN

From: Rick Jones <[email-masked]>
Date: Mon, 24 Aug 2015 10:27:00 -0700

On 08/24/2015 09:19 AM, Santosh R wrote:
>   Hi,
>
>     Earlier I was seeing lower throughput in VMs using VxLan as GRO was
> not happening in VM.
> Tom Herbert suggested to use "vxlan: GRO support at tunnel layer" patch series.
> With today's net-next (4.2.0-rc7) in host and VM, I could see GRO
> happening for vxlan, macvtap and virtual interface in VM.
> The throughput is still low between VMs (around 4Gbps compared to
> 9Gbps without VxLAN).

Out of curiosity, have you tried tweaking gro_flush_timeout 
(gro_flush_interval?) for the VMs eth interface?  Say perhaps a value of 
1000?  (I'm assuming the VM is using virtio_net) Does the behaviour 
change if vhost-net is loaded into the host and used by the VM?

rick jones

For completeness, it would also be good to compare the likes of netperf 
TCP_RR between VxLAN and without.