Re: [ECOS] eth_recv out of MBUFs

[Stanislav Meduna <stano at meduna dot org>]

On 05.08.2011 09:51, Lambrecht Jürgen wrote:

> Be carefull: the eCos freeBSD stack has no timeouts on TCP connections I 
> believe, but often the PC stack has!

Well the TCP timeouts that are in place when the connection
is not sending any data are basically unusable on any
standard-conforming TCP/IP stack. Whoever designed
SO_KEEPALIVE the way it is specified was smoking something
quite strong...

> So the eCos TCP session stays alive, but the PC (used to test) stack 
> shuts down the TCP connection when the cable breaks (after a timeout, or 
> it can also detect the cable fault). And the TCPs are out of sync 
> (something like that), and then it uses a lot of sockets, and indeed (as 
> in your next mail) the timeouts are very big to free sockets.
> If that is your problem, I can ask my college: he recompiled ecos to 
> change the minute timeout to seconds.

This is most probably not the source of the problem I am seeing
in this test setup. Thanks for the hint anyway.

> With a slow device and big burst of data, I had to increase the space 
> for mbufs.

Well, but to what size? I'd like to know the formula to calculate
the worst-case mbufs needs based on the number of active TCP
and UDP sockets... I am probably asking for too much :(

My gut feeling is that the TCP windows of all open connections
do not fit into the allocated mbufs. I'll try to tune this
stuff - unfortunately the FreeBSD stack is not really
friendly here.

> Better use lwIP on memory-constrained devices. And lwIP is more actively 
> maintained..

This is on my todo list for quite a long time - unfortunately
there are issues that have to be solved first. AFAIK lwIP
is not thread-safe on a single socket level and our present
framework does read from and write to a single socket from
different threads :/

I have also no idea whether everything from eCos we are
using/planning to use is able to work with lwIP (e.g. SNMP).


Regards
-- 
                                       Stano

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