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RE: [lwip-devel] Speed up lwIP

From: Goldschmidt Simon
Subject: RE: [lwip-devel] Speed up lwIP
Date: Fri, 4 May 2007 12:59:44 +0200

> Goldschmidt Simon wrote:
> > Hi all,
> > 
> > Talking about lwIP performance on this list, I have 2 issues which I

> > think could speed up lwIP (at least for me, they did):
> > 
> > - create a #define MEMCPY(dst,src,len) (defined to
> > as default) to be able to easily provide a faster memcpy than the
> > included in the C library. Especially if src or dst are not aligned,

> > writing my own memcpy gave me much better performance. I could
> > memcpy to my own version, but in my opinion, that's a dirty hack.
> This makes sense. Note that care may be required on when to 
> use MEMCPY instead of memcpy - GCC can optimise memcpy away 
> sometimes, particularly with a constant, relatively small 
> "len". That saves a function call. Maybe a second macro for 
> that case? SMEMCPY for small memcpy?

Yes, that's a good idea.

> > - (only for little endian processors and spectial MACs):
> > include some kind of define to tell the stack not to 
> convert items in 
> > protocol headers from host to network order if the MAC can do this.
> > This requires a rather advanced MAC, but still I think it's 
> important 
> > that we support this in order not to slow down MACs that have 
> > accelerating features.
> Perhaps you can just tell lwIP you are big-endian when you 
> aren't? Are there places where endianness is tested but not 
> for protocol headers?

The problem is the MACs are only capable of some protocols. If you
tell lwIP you are big-endian, you will lose all htonl-like functions
or have to define your own (which is bad also, since you'd have 2
having the same name). Either way, it's a hack since you're not
on a big-endian system (which is a shame, of course if you're developing
a networking system, but tell that altera...).

> OOI I've never seen such a MAC.

Guckst du hier: http://www.morethanip.com/mbps_10_100_1000_mac_acc.htm
This is an accelerating MAC for (altera?) FPGA systems (which I'm into,
at the moment). There are other ones, too. One would be the DMA-engine
I'm currently playing around with in my free-time... (And that, of
course, is the reason I'm making this roposal ;-)

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