On my laptop and amd64 system USB transfers to extern hard disk has nearly 100% CPU system usage according to htop. You can easily test it with encrypted partitions too. In htop the system/kernel usage is shown through the red bar and the user usage through the green one. Since you are a kernel developer it should be easy to find kernel task which uses much CPU so you can check the scaling under load. Important is that the user CPU usage isn't so high.
-- kernel does not scale cpu on system usage (only on user) https://launchpad.net/bugs/79232 -- ubuntu-bugs mailing list [email protected] https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
