Bad network performance over 2Gbps

[Anton Titov]

I use Linux for serving a huge amount of static web on few servers. When
network traffic goes above 2Gbit/sec ksoftirqd/5 (not every time 5, but
every time just one) starts using exactly 100% CPU time and packet
packet loss starts preventing traffic from going up. When the network
traffic is lower than 1.9Gbit ksoftirqds use 0% CPU according to top.

Uplink is 6 gigabit Intel cards bonded together using 802.3ad algorithm
with xmit_hash_policy set to layer3+4. On the other side is Cisco 2960
switch. Machine is with two quad core Intel Xeons @2.33GHz.

Here goes a screen snapshot of "top" command. The described behavior
have nothing to do with 13% io-wait. It happens even if it is 0%
io-wait.
http://www.titov.net/misc/top-snap.png

kernel configuration:
http://www.titov.net/misc/config.gz

/proc/interrupts, lspci, dmesg (nothing intresting there), ifconfig,
uname -a:
http://www.titov.net/misc/misc.txt.gz

Is it a Linux bug or some hardware limitation?

Regards,
Anton Titov

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