[PATCH net-next 0/3] tun: trim per-packet work on the write path

[Antonio Quartulli <antonio@mandelbit.com>]

Profiling a link-bonding daemon on an embedded router (Cortex-A7), which
injects every packet with a write() to a tun device, showed tun doing
per-packet work its packets do not need:

1. a flow dissector run, only to set the transport header
2. a BH-disabled RCU section, only to check for an XDP program, which
   only TAP devices can have
3. the parsing of an all-zero virtio-net header without IFF_VNET_HDR

Per 1400-byte packet written and dropped at the raw table, instruction
counts (qemu -icount) drop by 6.5% for 1 (Cortex-A7), 2.3% for 2 and
1.6% for 3 (x86). The tun selftests pass.

Antonio Quartulli (3):
  tun: don't probe the transport header of packets written by userspace
  tun: don't disable BHs for the XDP program check of every packet
  tun: skip the virtio-net header parsing without IFF_VNET_HDR

 drivers/net/tun.c | 20 ++++++++++++--------
 1 file changed, 12 insertions(+), 8 deletions(-)

-- 
2.56.0