Kernel 4.0-rc2 tested. Problem remains.
In rc2 there was a minimal fglrx driver in the kernel so I was able to
get a more usual desktop and use the graphical system monitor app. The
manifestation of the problem is slightly different now. Total CPU usage
still goes to 24 - 25% when a USB 3.0 hub is plugged in, but the khubd
process does not seem to take excessive CPU time. Instead, the kworker
and ksoftirqd processes take it all up. The kworker thread(s) take in
total about 17% and the ksoftirqd thread(s) about 7%.
The problem remains the same in all other aspects. It is present with
hubs using the VIA or Genesyslogic chipsets. Excessive CPU usage
continues even after the external hubs are disconnected. The cure
remains to unbind and then bind the xhci_hcd driver serving the internal
USB 3.0 hub.
** Changed in: linux (Ubuntu)
Status: Incomplete => Confirmed
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https://bugs.launchpad.net/bugs/1425803
Title:
Driver problem with USB chipset VIA VL812-B2
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