Hello,

I'd like to report a regression that goes back to the 2015. I know it's damn
late, but the good thing is, the regression is still easy to reproduce, verify &
revert.

Long story short, starting with the commit 66e5133f19e9 ("vlan: Add GRO support
for non hardware accelerated vlan") - which first hit kernel 4.2 - NAT
performance of my router dropped by 30% - 40%.

My hardware is BCM47094 SoC (dual core ARM) with integrated network controller
and external BCM53012 switch.

Relevant setup:
* SoC network controller is wired to the hardware switch
* Switch passes 802.1q frames with VID 1 to four LAN ports
* Switch passes 802.1q frames with VID 2 to WAN port
* Linux does NAT for LAN (eth0.1) to WAN (eth0.2)
* Linux uses pfifo and "echo 2 > rps_cpus"
* Ryzen 5 PRO 2500U (x86_64) laptop connected to a LAN port
* Intel i7-2670QM laptop connected to a WAN port
* Speed of LAN to WAN measured using iperf & TCP over 10 minutes

1) 5.1.0-rc3
[  6]  0.0-600.0 sec  39.9 GBytes   572 Mbits/sec

2) 5.1.0-rc3 + rtcache patch
[  6]  0.0-600.0 sec  40.0 GBytes   572 Mbits/sec

3) 5.1.0-rc3 + disable GRO support
[  6]  0.0-300.4 sec  27.5 GBytes   786 Mbits/sec

4) 5.1.0-rc3 + rtcache patch + disable GRO support
[  6]  0.0-600.0 sec  65.6 GBytes   939 Mbits/sec

5) 4.1.15 + rtcache patch
934 Mb/s

6) 4.3.4 + rtcache patch
565 Mb/s

As you can see I can achieve a big performance gain by disabling/reverting a
GRO support. Getting up to 65% faster NAT makes a huge difference and ideally
I'd like to get that with upstream Linux code.

Could someone help me and check the reported commit/code, please? Is there
any other info I can provide or anything I can test for you?


--- a/net/8021q/vlan_core.c
+++ b/net/8021q/vlan_core.c
@@ -545,6 +545,8 @@ static int __init vlan_offload_init(void)
  {
  	unsigned int i;

+	return -ENOTSUPP;
+
  	for (i = 0; i < ARRAY_SIZE(vlan_packet_offloads); i++)
  		dev_add_offload(&vlan_packet_offloads[i]);