net/tun: implement ndo_set_rx_headroom

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ndo_set_rx_headroom controls the align value used by tun devices to
allocate skbs on frame reception.
When the xmit device adds a large encapsulation, this avoids an skb
head reallocation on forwarding.

The measured improvement when forwarding towards a vxlan dev with
frame size below the egress device MTU is as follow:

vxlan over ipv6, bridged: +6%
vxlan over ipv6, ovs: +7%

In case of ipv4 tunnels there is no improvement, since the tun
device default alignment provides enough headroom to avoid the skb
head reallocation.

Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

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Paolo Abeni 2016-02-26 10:45:40 +01:00 • committed by David S. Miller

parent 3a927bc7cf

commit eaea34b23c

1 changed files with 16 additions and 1 deletions

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17

drivers/net/tun.c

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