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

From: Enrico Murador - Research & Development - CET
Subject: Re: [lwip-users] Pbuf pool size and network interface
Date: Fri, 24 Jun 2011 18:19:26 +0200
User-agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv: Gecko/20110616 Thunderbird/3.1.11

Dear Kieran,

(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;
This is ok, as my application (luckily!) requires a very small MSS; I have set
the TCP window as 2 * MSS obtaining a window of about 620 bytes.
(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.


Ok, setting enough buffers is ok for me.
Do you now also if I can tell my netif to use (preallocate for DMA) all the PBUF_POOL buffers available?
It seems that no other part of Lwip code allocates PBUF_POOL buffers, and I'm trying to save some memory...

Thank you very much for your support and patience replying all my questions! ;)

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