Bad performance and slow response time with heavy I/O on encrypted volumes

I am using Kubuntu 9.04 with encrypted file systems.
When I am doing heavy I/O operations, like copying a 1 GB file, the system becomes practically unusable.
With top, I have noticed [kcryptd] taking up a lot of resources. The nice priority of the process is -5. Renicing it to 0 may help a bit, but not much. I have also noticed that while I renice kryptd to 0, some time later, it is back to -5. What gives?

This is probably a scheduling problem in the kernel.

My system is fairly modern: 2.5GHz Intel Core 2 Duo with 4GB RAM. Hardware power should not be the issue here.
I think it is very sad that performance with encrypted volumes is so bad, because it discourages people from securing their data on laptops, netbooks, etc. I have also experienced this on several different systems with very different hardware.

I have reported this bug on previous versions of Ubuntu back to, I think, 7.04. I am a bit disappointed, that it has not been addressed.

I hope that you will try and fix this issue.
Please tell me, if there is anything I can do to help fix it. I am not a kernel hacker, so I can not come up with a patch for this.