netdev - Re: [PATCH] - vxlan: gro not effective for intel 82599

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Date:	Sun, 28 Jun 2015 14:17:26 -0700
From:	Tom Herbert <tom@...bertland.com>
To:	Or Gerlitz <gerlitz.or@...il.com>
Cc:	Ramu Ramamurthy <sramamur@...ux.vnet.ibm.com>,
	"David S. Miller" <davem@...emloft.net>,
	Jiri Benc <jbenc@...hat.com>, James Morris <jmorris@...ei.org>,
	Linux Kernel Network Developers <netdev@...r.kernel.org>,
	pradeeps@...ux.vnet.ibm.com, J Kidambi <jkidambi@...ibm.com>
Subject: Re: [PATCH] - vxlan: gro not effective for intel 82599

On Sun, Jun 28, 2015 at 1:19 PM, Or Gerlitz <gerlitz.or@...il.com> wrote:
> On Fri, Jun 26, 2015 at 10:59 PM, Tom Herbert <tom@...bertland.com> wrote:
> [...]
>> Looks like GRO was never implemented for vxlan tunnels. The driver is
>> simply calling netif_rx instead of using the GRO cells infrastructure.
>> geneve is doing the same thing. For other tunnels which are used in
>> foo-over-udp (GRE, IPIP, SIT) ip_tunnel_rcv is called which in turn
>> calls gro_cells_receive.
>
> Tom,
>
> Since v3.14, when a tunneled (say VXLAN/GRE) packets are received on
> the physical interface, they go through GRO aggregation before being
> delivered up to the tunnel "device" (e.g either vxlan/gre netdevice or
> OVS vxlan/gre vport) -- so in that respect, can you elaborate a little
> further why we want to GRO them again?
>

If we don't have a verifiable checksum from the device GRO is not
applied to UDP encapsulated packets at the physical interface, but can
be done at the tunnel. Ramu is seeing poor performance because there
is no GRO at all is happening, so doing it at the tunnel is an
improvement. As I described before, avoiding checksum calculation in
the device NAPI still seems to be a good thing (in my testing I do see
a slight regression if we were to do the checksum in device NAPI).

btw, the real "fix" for this is for NICs to provide CHECKSUM_COMPLETE! :-)

Tom

> Or.
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