RE: [lwip-users] How to optimize raw UDP performance

[Bill Auerbach]

Which direction?  Improving sending and improving receiving are 2 different
problems.  They overlap some, but the focus is different.

Something's not right if offloading was used and it didn't help - it should
double to quadruple the speed.  Try turning off CHECKSUM_GEN_UDP and
CHECKSUM_CHECK_UDP.  Offloading or doing the checksum in hardware is one
critical item.  As is optimizing memory and memory copies (using a DMA
memcpy over the standard C memcpy is huge).  Using zero-copy drivers for
sending and/or receiving is huge (because you're not copying).

I spent 2+ months optimizing lwIP - at first for TCP, which although I
doubled, wasn't nearly fast enough.  We switched to UDP and proved the speed
was adequate to move forward.  Then I wrote a reliable UDP protocol (not
hard to do, but had to be done since we can't lose data).  Some of my
optimizations were submitted but some may be target dependent (i.e. little
endian improvements or specific to my variant of GCC).  I've pushed the past
2 years for better performance and I realize resources are limited to
support it as well as it's not a top priority for the goals of lwIP (Light
Weight being the key words here).  For most users I suspect what we have is
fast enough - plus it's a very good and reliable implementation of TCP/IP.

Documented speed has a lot to do with the platform.  On a high speed PowerPC
with assembly internet checksum and DMA memory copies, lwIP met our needs
without any other changes or optimizations except a low level UDP/ICMP/ARP
packet filter (in low_level_input) while in our "high bandwidth" mode.  We
didn't have to do this - I just didn't want a UDP or ICMP burst to disrupt
system timing.  On a lower speed FPGA project, a lot of effort was put into
lwIP and supporting code and the FPGA to meet our goals.

Bill



>-----Original Message-----
>From: address@hidden
>[mailto:address@hidden On
>Behalf Of bobbyb
>Sent: Wednesday, September 23, 2009 4:02 PM
>To: address@hidden
>Subject: [lwip-users] How to optimize raw UDP performance
>
>
>What are some good techniques for improving UDP performance in raw mode.
>Right now i'm getting approximately 82Mbits/sec. I would like to
>increase
>that to 150+ Mbits/sec which should be possible according to the
>documentation. I've tried increasing various buffer/memory sizes with
>very
>small effects. I also setup checksum offloading which surprisingly had
>no
>effect on performance.
>
>Does anyone know any other techniques worth trying? Why is the
>documented
>speed so much higher than what I'm getting?
>
>Thanks
>--
>View this message in context: http://www.nabble.com/How-to-optimize-raw-
>UDP-performance-tp25531280p25531280.html
>Sent from the lwip-users mailing list archive at Nabble.com.
>
>
>
>_______________________________________________
>lwip-users mailing list
>address@hidden
>http://lists.nongnu.org/mailman/listinfo/lwip-users