Jackd Problems -- alsa_pcm: xrun of at least 1227061150613.504 msecs

[Jonathan Ryshpan]

In the past I've never had any problems running jackd.  Now I'm getting
a very large number of messages reading:
        **** alsa_pcm: xrun of at least 1227061150613.504 msecs
I'm running F9 on an x86_64 system with all updates installed.
Pulseaudio is not running.  Jackd is started via qjackctl.  No past
problems with audio beyond the usual conflicts between pulseaudio and
firefox.

Questions:
(1) What exactly does this message mean?  An "xrun" is a buffer under-
or over-run -- but what does the time interval represent?

(2) Whatever the time interval means, it looks rather large.
1227061150613.504 msec is many days (or maybe years if msec means
millisec and not microsec)  This looks like a misconfiguration of some
kind or a missing component.  Any idea what it might be?

Here is the start of the qjackctl log of the session.

18:53:38.317 Patchbay deactivated.
18:53:38.364 Statistics reset.
18:53:38.566 ALSA connection graph change.
18:53:38.752 ALSA connection change.
18:53:41.050 Startup script...
18:53:41.050 artsshell -q terminate
18:53:42.247 Startup script terminated with exit status=256.
18:53:42.261 JACK is starting...
18:53:42.262 /usr/bin/jackd -R -dalsa -dhw:0 -r48000 -p1024 -n2
18:53:42.267 JACK was started with PID=3423.
jackd 0.109.2
Copyright 2001-2005 Paul Davis and others.
jackd comes with ABSOLUTELY NO WARRANTY
This is free software, and you are welcome to redistribute it
under certain conditions; see the file COPYING for details
JACK compiled with System V SHM support. 
loading driver ..
apparent rate = 48000
creating alsa driver ... hw:0|hw:0|1024|2|48000|0|0|nomon|swmeter|-|
32bit
control device hw:0
configuring for 48000Hz, period = 1024 frames (21.3 ms), buffer = 2
periods
ALSA: final selected sample format for capture: 16bit little-endian
ALSA: use 2 periods for capture 
ALSA: final selected sample format for playback: 16bit little-endian
ALSA: use 2 periods for playback
**** alsa_pcm: xrun of at least 1227061150613.504 msecs
**** alsa_pcm: xrun of at least 1227061150613.504 msecs
**** alsa_pcm: xrun of at least 1227061150613.504 msecs
**** alsa_pcm: xrun of at least 1227061150613.504 msecs
...