Sorry I meant "using udp the CPU load was at 100% but using TCP the load was at about 20% independent on the mtu"!!!
I've posted the whole command I used to disable the tcp offload!
"ethtool -K eth5 rx off tx off sg off tso off gso off gro off lro off"
As i don't have segmentation "ethtool -K eth5 rx off tx off" would be enough I would say, right?
I've had a look at the Datasheet and it looks like UDP and TCP checksum offload is implemented.
I have scientific linux 6 running. Kernel 2.6.32. Do you think it is possible that the kernel cannot use the udp offload but the tcp offload works?
Or does somebody have another idea why my tcp communication generates much less CPU load?
You can see a diagram at http://butler.physik.uni-mainz.de/~k...to_perf-2p.pdf