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Re: [lwip-users] Improving LWIP performance

From: Kieran Mansley
Subject: Re: [lwip-users] Improving LWIP performance
Date: Thu, 05 Aug 2010 10:03:02 +0100

On Tue, 2010-08-03 at 19:20 -0400, Karthik Vadambacheri Manian wrote:
> So my questions are:
> 1) Why do checksum errors occur even though I run everything in a
> virtual machine and no hardware is involved? How can I reduce this?

I would guess a bug in your system.  To reduce it fix the bug!  For
example, if there was a problem with a packet buffer being reused before
the previous data had been sent you would see the data in the first
packet corrupted with contents from a later one.  The checksum would now
show up this error.  I would look at the packets (through a packet
capture) that have checksum errors and see if it's either that the
payload is incorrect (e.g. for each iteration set payload of your
ping-pong packets to the number of the iteration and look for values out
of order) or if the checksum has been computed wrongly.

> 2) How can I prevent acknowledgements from missing so that
> retransmissions can be avoided?

Packets can be dropped or not sent for lots of reasons.  The most
obvious would be a shortage of packet buffers.  You can use the
LWIP_STATS code to monitor most of lwIP's internal resources and then
when you print out the output it will show what (if anything) has been
exhausted.  You can then tune the allocation of resources to provide

> 3) Some general tips on increasing performance with LWIP is much
> appreciated.

Take a look at the lwIP wiki - Simon wrote a good introduction to this a
few months ago.


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