From: Paolo Abeni <pab...@redhat.com>
Date: Thu, 30 Nov 2017 15:35:33 +0100
> After commit 3a927bc7cf9d ("ovs: propagate per dp max headroom to
> all vports") the need_headroom for the internal vport is updated
> accordingly to the max needed headroom in its datapath.
>
> That avoids the pskb_expand_head() costs when sending/forwarding
> packets towards tunnel devices, at least for some scenarios.
>
> We still require such copy when using the ovs-preferred configuration
> for vxlan tunnels:
>
> br_int
> / \
> tap vxlan
> (remote_ip:X)
>
> br_phy
> \
> NIC
>
> where the route towards the IP 'X' is via 'br_phy'.
>
> When forwarding traffic from the tap towards the vxlan device, we
> will call pskb_expand_head() in vxlan_build_skb() because
> br-phy->needed_headroom is equal to tun->needed_headroom.
>
> With this change we avoid updating the internal vport needed_headroom,
> so that in the above scenario no head copy is needed, giving 5%
> performance improvement in UDP throughput test.
>
> As a trade-off, packets sent from the internal port towards a tunnel
> device will now experience the head copy overhead. The rationale is
> that the latter use-case is less relevant performance-wise.
>
> Signed-off-by: Paolo Abeni <pab...@redhat.com>
Applied, thanks.
