[Bug 226968] IRQ storm on cpu0 timer when holding down key on USB keyboard

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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=226968

            Bug ID: 226968
           Summary: IRQ storm on cpu0 timer when holding down key on USB
                    keyboard
           Product: Base System
           Version: CURRENT
          Hardware: Any
                OS: Any
            Status: New
          Severity: Affects Some People
          Priority: ---
         Component: usb
          Assignee: freebsd-usb at FreeBSD.org
          Reporter: johalun0 at gmail.com

I noticed this when playing a first person shooter with keyboard controls.
To verify, do the following:

Open a terminal window (I used xfce4-terminal)

Run 
$ systat -vmstat

On the USB keyboard, hold down some key like 'a'.
All is normal at this stage. 

Without releasing 'a', press and release another key, like 'b'.

See the irqs on cpu0:timer go up to several hundred thousand.

Release 'a' and it will go back to normal. 


USB debug information (hw.usb.xhci.debug=16) does not show abnormal amounts of
interrupts.

With this bug, playing a fps-like game with keyboard controls is impossible
since the whole game lags during irq storm.

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