tso_segsz and mss above jumbo MTU in FreeBSD 7

Yony Yossef yonyossef.lists at gmail.com
Tue Jun 10 08:25:42 UTC 2008


Hi All.

I'm working on a 10GigE driver for FreeBSD 7.

Looking at other GigE and 10GigE drivers I've seen that
mbuf->m_pkthdr.tso_segsz is assigned to MSS (Max Segment Size) on the Tx
routines.
If I understand correctly the tso_segsz is supposed to inform the driver
with the MTU set by the OS, therefore it should change upon ifconfig mtu
commands.
When I set my MTU to 9600 I still recieve tso_segsz=1500 in the Tx mbufs
from the OS.

Where's my mistake here?

Yony


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