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Date:   Mon, 20 Jul 2020 13:38:07 -0400
From:   Alan Stern <stern@rowland.harvard.edu>
To:     Michal Hocko <mhocko@kernel.org>
Cc:     LKML <linux-kernel@vger.kernel.org>,
        Greg KH <gregkh@linuxfoundation.org>,
        linux-usb@vger.kernel.org, "Rafael J. Wysocki" <rjw@rjwysocki.net>
Subject: Re: kworker/0:3+pm hogging CPU
Message-ID: <20200720173807.GJ1228057@rowland.harvard.edu>
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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