Re: [lwip-devel] How many MEMP_NUM_TCP_SEG needed?

[Simon Goldschmidt]

narke <address@hidden> wrote:
> I set MEMP_NUM_TCP_SEG as same as TCP_SND_QUEUELEN.  I thought this
> should be okay because I always disable the nagle and always call the
> tcp_output after called tcp_write().    So, in the case, each sending
> should resulted in one tcp segement, so the MEMP_NUM_TCP_SEG should be
> same value as current send queue length.  However, in some of my
> tests, I observed, my pcb's snd_queuelen did not go beyond the
> TCP_SND_QUEUELEN, but the TCP_SEG memory poll get used out --
> allocation failed and the err counter of lwip_stats.memp[x] get
> increased.
> 
> How can I understand this and how do I set the MEMP_NUM_TCP_SEG const?

- Are you using more than one pcb? MEMP_NUM_TCP_SEG is a global value, while 
TCP_SND_QUEUELEN is per pcb.
- When TCP_QUEUE_OOSEQ is enabled, each incoming out-of-sequence segments 
requires one MEMP_TCP_SEG.
- Finally, segments including flags only (SYN/FIN) need one MEMP_TCP_SEG, too.

Simon
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