RE: [lwip-devel] tcp_input: order of processing question/comment

[Pettinato, Jim]

I didn't bother to go look, but I seem to recall the likelihood of an
updated receive window being part of the reason for calling tcp_output
_after_ the recv callback?? I'm not sure it would harm anything to call
it _prior_ to the recv callback as well, but I agree we should still
call it afterward.

- Jim  

-----Original Message-----
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Sent: Wednesday, February 04, 2009 12:06 PM
To: lwip-devel
Subject: Re: [lwip-devel] tcp_input: order of processing
question/comment

I guess the intention was to be able to output data enqueued in the recv
callback. _If_ changing anything, we could add a _second_ call to
tcp_output _before_ calling the recv callback, but the call _after_ the
recv callback has to remain there, I think.


Simon


bill wrote:
>
> Currently In tcp_input, towards the end of the function, the tcp_recv 
> callback is called and if there is no error returned, tcp_output is 
> called to process any pending outgoing data.
>
> The questions are: Why would we want an error returned by the receive 
> callback to prevent us from sending any pending data? Wouldn't we 
> still want to send queued ACKs or queued data?
>
> The comment is: It would seem to be better to call tcp_output
> **before** calling the tcp_recv callback. This would allow the other 
> end of the connection to process any data that may be sent in that 
> call while the lwIP side goes off and processes its data in the 
> receive callback. In my bandwidth testing I do see slightly better 
> performance by adding a tcp_output call before the receive callback.
>
> Bill
>
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