RE: [lwip-users] Optimizations forapplications requiring limitedfunctionality.

[Matthew Yingling]

----Original Message----
From: address@hidden
[mailto:address@hidden Behalf Of
Roger Cover
Sent: Wednesday, April 18, 2007 1:03 PM
To: Mailing list for lwIP users
Subject: RE: [lwip-users] Optimizations forapplications requiring
limitedfunctionality.

> Greetings All,
>
> I have made a discovery about my problem. I upgraded to version 9.1
> of the Xilinx EDK at the same time I upgraded to lwIP 1.2.0. This EDK
> upgrade changed the GNU compiler suite that I am using. The new
> version of the compiler is the source of my problem. It generates
> much less efficient code, even with optimizations turned up.
>
> The time spent in the lwIP library (for my UDP transfer) is now only
> 4.2% of the total transfer time. The bulk of the transfer time is in
> the Xilinx driver code (82%). The suggestions I received (thanks to
> Frédéric Bernon) to remove unused options from lwIP did reduce the
> time used by the lwIP library. Unfortunately, that was not my
> problem.
>
> I am not sure why the new version of the compiler is so much less
> efficient. The old compiler produced code that transferred my
> 33554432-byte dataset in 5.8 seconds. The code produced with new
> compiler takes 8.8 seconds (62.5% of the throughput performance). I
> will be looking into that.
>
> My mistake was in presuming that the same driver source code would
> produce the same executable code under EDK 8.1 and EDK 9.1. That led
> me to the incorrect conclusion that the difference in performance was
> in the new lwIP library. Thank you all for your help.
>
> Regards,
> Roger W. Cover
>

Hi Roger,

Xilinx upgraded their compiler from GCC 3.4.1 to 4.1.1 between EDK 8.2 and
9.1.  If you are confident the compiler is creating less efficient code, I
recommend you open a case with them.  I have no experience with the new EDK,
but I suspect the new compiler may not be fully optimized yet.

Matthew