Re: TCP_MAXSEG vs TCP/generic segmentation offload (tso/gso)

[nisse@lysator.liu.se (Niels Möller)]

Eric Dumazet <eric.dumazet@gmail.com> writes:

> I believe TCP_MAXSEG is working fine, but GRO/GSO dont care at all :
> They coalesce frames whatever their size is.

I was under the impression that TSO (and maybe GSO) implied more
cleverness in the network card; that the network card more or less gets
to decide by itself how to divide a tcp stream into segments. And for
example in the atl1c driver which I looked a bit into, this was what the
REG_MTU register was for. Seems I have gotten this totally wrong.

Maybe Documentation/networking/netdevices.txt could clarify how it
works. Currently, it says

: Segmentation Offload (GSO, TSO) is an exception to this rule.  The
: upper layer protocol may pass a large socket buffer to the device
: transmit routine, and the device will break that up into separate
: packets based on the current MTU.

Regards, and thanks for your patience,
/Niels

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