I've also run into trouble with the USB 3 port. Before I try a solution, I want to post for posterity some of the symptoms I've been experiencing so that if someone else runs into the same problems, they'll have an idea of what is causing it.
If I plug my Logitec G11 keyboard into my USB 3 port, I get the following symptoms:
1. I get a kworker process eating the CPU up to about 75%.
2. Running "perf top" shows the kernel spending its time as follows:
Unplugging the keyboard does nothing.
samples pcnt function DSO
_______ _____ ___________________________________ _________________
4740.00 26.9% acpi_os_read_port [kernel.kallsyms]
2768.00 15.7% acpi_ex_system_memory_space_handler [kernel.kallsyms]
1387.00 7.9% acpi_os_write_port [kernel.kallsyms]
1202.00 6.8% acpi_ns_search_one_scope [kernel.kallsyms]
420.00 2.4% acpi_ns_check_for_predefined_name [kernel.kallsyms]
342.00 1.9% intel_idle [kernel.kallsyms]
284.00 1.6% __ticket_spin_lock [kernel.kallsyms]
225.00 1.3% kmem_cache_alloc [kernel.kallsyms]
Workaround: To get rid of the runaway kworker process, I put the laptop to sleep and resume.
Just like haakon, my USB 3 port is driven by ehci instead of xhci.