[GitHub] [incubator-nuttx] anchao edited a comment on pull request #2489: [Performance]net/tcp: send the ACK in time after obtain ahead buffer from iobs

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anchao edited a comment on pull request #2489:
URL: https://github.com/apache/incubator-nuttx/pull/2489#issuecomment-742164923


   > @anchao
   > 
   > Let me confirm this PR.
   > 
   > Does this PR relate to TCP ZeroWindow report and TCP Window update
   > after IOB is available on NuttX?
   
   Hi @masayuki2009 san,
   
   Thanks for your review!
   Yes, in the previous commit, , I removed the slide of the default acceptance window to avoid excessive tcp retransmissions if the iob is unavailable,
   
   https://github.com/apache/incubator-nuttx/blob/375211f5a176ce5a3cdaa36ed8a5cbddddf1fedf/net/tcp/tcp_recvwindow.c#L159-L167
   
   Unfortunately, if too much tcp data is received without waiting in recv() (e.g HTTP GET), 
   then the stack will unable to reply ACK normally in the subsequent reception,
   The window will remain at 0 and the transfer cannot be continued ...
   
   This PR solves a similar issue, If the recv window slide in the previous ACK is 0,
   send an ACK to update the current window slide after recv().


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