Re: [lwip-users] Unable to allocate TCP_SEG

[Jonathan Larmour]

Josh Rothstein wrote:
> One more behavioral thing I noticed:
>
>  
>
> If I do lwip_send() and watch the debug output I will see the TCP header 
> information showing the stack received an ack for that packet.   If I do 
> a couple more lwip_send(), I will eventually stop seeing the TCP header 
> information and the tcp_enqueue() will begin to fill with TCP_SEGs.  I 
> if then close() the socket all the pending receives will then come 
> through the debug output. How can I stop this bottleneck?

Sounds like your tcpip_thread is getting stuck somewhere. Can you stop it 
and see where it is? Have you got a safe implementation of SYS_ARCH_PROTECT?

> Further examination shows that the problem lies within tcpip.c. For some 
> reason tcpip_input() fails when trying to memp_malloc(MEMP_TCPIP_MSG). 
> This occurs before tcp_enqueue() fills the MEMP_TCP_SEG pool. 
> tcpip_thread() does call memp_free(MEMP_TCPIP_MSG, msg) at the end of 
> the loop, so I am at a loss as to why the MEMP_TCPIP_MSG pool fills up.

This also points to tcpip_input blocking on something. What happens when 
mailboxes on your system fill up... does the relevant thread block? You 
may want to output a diagnostic in your port's sys_mbox_post function to 
check if this is what's happening.

Alternatively is your tcpip thread getting starved by some other busy 
thread in the system and never actually able to run and make progress with 
processing the packets?

Jifl
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