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Opened 3 years ago

Last modified 2 years ago

#18296 new enhancement

Jumbo frame limited to 4070 MTU on Archer C7 (ar71xx/ag71xx)

Reported by: martin Owned by: developers
Priority: normal Milestone: Chaos Calmer 15.05
Component: kernel Version: Trunk
Keywords: Cc:

Description

The QCA9558 SOC and the AR8327N-BL1A switch on the TP-Link Archer C7 router both support 9000 MTU jumbo frames. However, the ag71xx Ethernet driver seems to be passed a dev with an MTU around 4K. Ideally we could use an MTU of 4096 or 8192 so it's a multiple of 4K pages, but I don't see where the limit is set in the drivers.

root@archer:~# ifconfig eth1 down
root@archer:~# ifconfig eth1 mtu 9000
ifconfig: SIOCSIFMTU: Invalid argument
root@archer:~# ifconfig eth1 mtu 4072
ifconfig: SIOCSIFMTU: Invalid argument
root@archer:~# ifconfig eth1 mtu 4070
root@archer:~# ifconfig eth1 up

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Change History (1)

comment:1 Changed 2 years ago by daggs@…

you can find it at https://dev.openwrt.org/browser/trunk/target/linux/ar71xx/files/drivers/net/ethernet/atheros/ag71xx/ag71xx.h?rev=46280#L53

I'm having the same issue, I get 20Mb/s on a cable connection.
I can try to compile it with higher mtu but I don't know how to upgrade the firmware.
btw, how did out found out what is the max possible?

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