Re: [lwip-users] performance in sending / receiving

[Robert Goeffringmann]

Hi Kieran,
I'm sorry for the delay in getting back to you, I've been busy with exams 
lately. :/

> Having had a look at your ethereal captures I see it advertising up to
> around 42KB.  A full capture (from the start of a connection) in pcap
> rather than txt format would enable me to look at this more precisely.

> Actually, in this case (with the benefit of looking at your packet
> capture) it looks like the stack is processing the packets at a
> reasonable rate (the ACK numbers are increasing) but the window is still
> decreasing.  This suggests that the packets are being buffered in the
> sockets API layer, and the application is not reading them fast enough.
> ie. This could be a scheduling issue.

That'd make sense.
The PS2 kernel doesn't do any automatic scheduling, it'll simply execute the 
thread with the highest priority which is not waiting for a semaphore or 
messagebox at the moment.

right now I have the threads structured like this (highest to lowest 
priority):

- highest priority is the thread for the HW interface, it takes lwip's 
packets from a queue and passes them to the HW (or reads them from the HW 
and passes them to lwip...)
- the next thread is the timer thread, which only calls tcp_tmr and 
etharp_tmr periodically
- then there's lwip's tcp/ip thread
- and the lowest thread is the application doing the the send/recv calls.

This structure has worked pretty well for sending data, but indeed it did 
seem to cause those zero-windows.
I've changed it and made the tcp/ip thread the one with the lowest priority 
and it fixed that... but unfortunately it has rather little influence on the 
receive speed.
With the application having the lowest priority, I had transfer rates of 
~1,6MB/s (average), with the actual transmission speed varying between 1,3 
and 2,0 MB/s.
If the tcp/ip thread has the lowest priority, the average speed is ~1,8MB/s, 
varying between 1,0 and 1,9 MB/s.

I uploaded the pcap files and lwip's statistics here:
http://www.goeffringmann.de/lwip/thprio.zip

the prio1 file is the one with the application having the lowest priority, 
in prio50 it's the tcp/ip thread.

Is there anything like a suggested model for those thread priorities?

I also wrote a checksum routine in assembly, but no matter if I use that one 
or lwip's most basic one doesn't have any difference at all on either 
sending- or receiving speed. So I suppose I can assume that cpu power is not 
the bottleneck... right?

Thanks a lot for your help,

Robert.