linux-kernel - Re: kworker/0:3+pm hogging CPU

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Date:   Mon, 20 Jul 2020 19:45:30 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Alan Stern <stern@...land.harvard.edu>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Greg KH <gregkh@...uxfoundation.org>,
        linux-usb@...r.kernel.org, "Rafael J. Wysocki" <rjw@...ysocki.net>
Subject: Re: kworker/0:3+pm hogging CPU

On Mon 20-07-20 13:38:07, Alan Stern wrote:
> 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).

Would that help to pinpoint the problem down?

> 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.

Yes, that helped to put some relief to the machine. 

-- 
Michal Hocko
SUSE Labs