Very high IRQ load causing horrible iSCSI performance

[dinominant]

I've setup a RAID6 iSCSI target on a Gentoo system. When I read data with the initiator I see ~100MBps on each network adapter. It's excellent because the bottleneck is the ethernet port and not the RAID array. However when I try to write to the array (via iSCSI) I see huge system CPU load and the performance drops to ~2MBps.

I'm suspecting it's related to a large amount of interrupts flooding the CPU and the system has no time to do anything but get interrupted.

What can I do to fix this -- or even verity that the IRQ load is the problem??

[dinominant]

Due to time constraints I will have to revisit this problem at a later date. I did have better performance and I believe the issue was an MTU mismatch between the target and the initiator but I cannot verify that this was the case until I can spend some more time on this system.