Re: kworker/0:3+pm hogging CPU

Alan Stern
2020-07-20T17:38:10Z

On Mon, Jul 20, 2020 at 06:33:55PM +0200, Michal Hocko wrote:
> On Mon 20-07-20 11:12:55, Alan Stern wrote:
> [...]
> > sudo echo 'module usbcore =p' >/debug/dynamic_debug/control
> >
> > Then wait long enough for some interesting messages to appear in the
> > kernel log (it should only take a few seconds if the worker thread is as
> > busy as you say) and collect the output from the dmesg command.
> >
> > To turn dynamic debugging back off when you're finished, use the same
> > command with "=p" changed to "-p".
>
> [ 95.395815] hub 2-0:1.0: state 7 ports 6 chg 0006 evt 0000
> [ 95.395824] usb usb2-port1: status 0088, change 0000, 5.0 Gb/s
> [ 95.395838] usb usb2-port2: status 0088, change 0000, 5.0 Gb/s
> [ 95.396016] hub 2-0:1.0: hub_suspend
> [ 95.396023] usb usb2: bus auto-suspend, wakeup 1
> [ 95.396029] usb usb2: bus suspend fail, err -16

Okay, that's the problem. You may get more specific information about
the suspend failure if you turn on dynamic debugging for the xhci-hcd
module (same command as above but with xhci-hcd instead of usbcore).

If you want a quick way to prevent this from happening, you can do:

sudo echo on >/sys/bus/usb/devices/usb2/power/control

That won't actually fix anything, but it will stop the system from
automatically trying to suspend usb2 root hub.

Alan Stern