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From: wkevin on 23 Apr 2010 07:38
Hello,
There is a feature called "TCP segmentation offload" which is
supported in some Linux drivers (e1000 and more).
You can know that a device driver has support for TSO by "eththook -k
deviceName" and looking at the value of
"tcp-segmentation-offload".
However, I saw that in the kernel there is also support for
TCP segmentation in layer 4.

To be more specific:
the gso_segment member of
tcp_protocol is the tcp_tso_segment() method
see: net/ipv4/af_inet.c

dev_hard_start_xmit() checks
netif_needs_gso(dev, skb) and when it returns 0, this causes us not to
call dev_gso_segment(), and as a result
tcp_tso_segment() is not called.

How can we use the layer 4 TCP segmentation ?
Or in fact, how can we force netif_needs_gso() to return true (of
course without changing the kernel code of this method, since this is
not a proper way. there should be a way to use L4 TSO on devices
without driver TSO).

Rgs,
Kevin





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