Re: [lwip-users] RE: [Virtex II Pro] pbuf / DHCP / lwIP upgrade to EDK/upgrade to EDK 9.1i (Louis Filasky) (Goldschmidt Simon) (Arden Llewellyn)

[Kieran Mansley]

On Thu, 2007-06-21 at 11:05 -0700, Arden Llewellyn wrote:
> I finally got things working (mostly anyway), the last thing I needed
> to add was a call to lwip_socket_init() in lwip_init_proper() (see
> xemacif.c).  I can connect to my server application via TCP, I can
> send data, and in general things are working.  The problem is that
> once data starts being transmitted in both directions (server ->
> client and client -> server), with some data being un-solicited, I
> start seeing big delays in the data.  I tried turning debug on, but
> there is too much debug and it changes timing so much that things get
> worse.  I tried dumping tcp stats, but it doesn't look like I am out
> of any resources.  Basically, I see a burst of good transfers, then
> retransmissions every 300 ms which kills throughput.  If I stop the
> data, then wait a second or two, start it back up, I get a good burst,
> then the retransmissions start again.  I have attached an ethereal
> capture.  Any ideas?  By the way, I guess I don't know the rules of
> attachments, hopefully this works.

You're getting packet loss, which results in retransmissions and the TCP
protocol cutting its data rate to try and prevent further packet loss.
The best way to improve this is to try and working out where the packets
are getting dropped.  lwIP would normally only drop packets if it was
out of packet buffers, and you say you don't think it's running out of
resources.  Could it be that lwIP is just not fast enough and the
packets are getting dropped by your hardware?

Kieran