Re: [lwip-devel] tcp_output does not force seg sent out

[narke]

On 9 March 2012 15:08, Simon Goldschmidt <address@hidden> wrote:
> narke <address@hidden> wrote:
>> I found it's not always that the tcp_output() call can make a segment
>> to be sent out.   Sometimes it still accumulated data until TCP_MSS
>> reached before output a segment.
>
> That's the nagle algorithm (-> google). In short, it tries to limit the 
> overhead of ACK segments by sending as little segments as possible by 
> combining multiple calls to write() into a single segment.
>
>> In what situation that tcp_output()
>> does not output segment?
>
> A segment is sent tcp_do_output_nagle() results in 1:
>
> #define tcp_do_output_nagle(tpcb) ((((tpcb)->unacked == NULL) || \
>                            ((tpcb)->flags & (TF_NODELAY | TF_INFR)) || \
>                            (((tpcb)->unsent != NULL) && 
> (((tpcb)->unsent->next != NULL) || \
>                              ((tpcb)->unsent->len >= (tpcb)->mss))) || \
>                            ((tcp_sndbuf(tpcb) == 0) || (tcp_sndqueuelen(tpcb) 
> >= TCP_SND_QUEUELEN)) \
>                            ) ? 1 : 0)
>
> In other words, if there is unacked data, we wait for it to be acked or to 
> send a full segment (unless we are in fast retransmit or ran out of lwIP 
> buffers).
>
>> And, how do I ensure the output behavior
>> really happen?
>
> Call tcp_nagle_enable(pcb).
>
>
> Simon

Thanks, Simon.   But the naming is a little confusing to me.   nagle
means no-agle?

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narke
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