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Re: [lwip-users] Pbuf pool size and network interface

From: Kieran Mansley
Subject: Re: [lwip-users] Pbuf pool size and network interface
Date: Fri, 24 Jun 2011 09:39:11 +0100

On Thu, 2011-06-23 at 17:08 +0200, Enrico Murador - Research &
Development - CET wrote:
> Supposing I have a 500 bytes TCP_WND size, and my server application 
> allows 10 simultaneous TCP connections;
> do I need at least (10 * 500) bytes of total pbuf pool space
> (available 
> to the network interface) to be sure to avoid "TCP deadlocks"?

Two things: (1) 500 bytes is a very small window.  Please make sure you
set it to be at least 2*MSS to avoid very poor TCP performance; (2) if
you have less than connections*TCP_WND buffer space, then in the worst
case of them all sending at once, you would drop data.  This shouldn't
lead to a deadlock as the other end will retransmit, but (i) it will
result in poor performance and (ii) it is rather wasteful of CPU and
bandwidth resources as both sides have gone to some effort to send and
receive the data, and if it gets dropped that effort is lost.


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