Re: [lwip-users] Sending large packets

[Jonathan Larmour]

Goldschmidt Simon wrote:
> Scatter-gather at driver level? I thought that's mandatory (at least for 
> TCP)!

It isn't. TCP has no relationship to the presence of scatter gather. Not 
even socket APIs (despite any presence of readv()/writev()). Certainly s-g 
exists in high-end and some mid-range ethernet MAC chips, but cheap, 
cheerful and popular MACs like CS8900a don't support it.

> As to your problem, Julian, it might help to increase the limiting 
> defines as it seems that TCP is somehow limited and can't fill pbufs up 
> to MTU size at all times. So you should check the configured TCP window 
> and TCP_SNDQUEUELEN (or what it's named, that's the count of pbufs 
> simultaneously being enqueued). TCP slow start might also limit the 
> segment size on connection start.

I'm not sure Joolz said it was at connection start.

Joolz, as well as what Simon and Kieran have said, I think you need to look 
at a packet trace (with ethereal or tcpdump), so in particular you can see 
what the receive window of the peer is at the point these packets are sent.

Jifl
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