Surprisingly high interrupt rate on idle machine's uhci controller on 7.1

[James Seward]

Hello,

While checking out the -P option for top in 7.1 I noticed that my
desktop at home (which is currently idle) was spending nearly 100% of
one core on interrupt:

last pid:  5678;  load averages:  0.00,  0.00,  0.00
59 processes:  1 running, 58 sleeping
CPU 0:  0.0% user,  0.0% nice,  0.0% system,  0.0% interrupt,  100% idle
CPU 1:  0.0% user,  0.0% nice,  0.8% system,  0.0% interrupt, 99.2% idle
CPU 2:  0.0% user,  0.0% nice,  0.0% system,  0.0% interrupt,  100% idle
CPU 3:  0.0% user,  0.0% nice,  0.0% system, 90.3% interrupt,  9.7% idle

So I looked at vmstat -i:
interrupt                          total       rate
irq16: nvidia0 em*               5009831         88
irq18: uhci2 ehci+                 66595          1
irq19: uhci4++                2855320585      50637
irq22: pcm0                       213238          3
irq23: uhci3 ehci1                     1          0
cpu0: timer                    112447860       1994
cpu1: timer                    112444767       1994
cpu3: timer                    109457852       1941
cpu2: timer                    109457830       1941
Total                         3304418559      58602

The interrupt rate for uhci4 seems very high for an idle system.

% dmesg | grep uhci4
uhci4: <UHCI (generic) USB controller> port 0xb400-0xb41f irq 19 at
device 29.1 on pci0
uhci4: [GIANT-LOCKED]
uhci4: [ITHREAD]
usb5: <UHCI (generic) USB controller> on uhci4

% dmesg | grep usb5
usb5: <UHCI (generic) USB controller> on uhci4
usb5: USB revision 1.0
uhub6: <Intel UHCI root hub, class 9/0, rev 1.00/1.00, addr 1> on usb5
usb7: companion controllers, 2 ports each: usb4 usb5 usb6

% usbdevs -v
...
Controller /dev/usb5:
addr 1: full speed, self powered, config 1, UHCI root hub(0x0000),
Intel(0x0000), rev 1.00
 port 1 powered
 port 2 powered

Nothing is plugged in there!

The only USB devices I have plugged in are:
addr 1: EHCI root hub, Intel
 addr 2: USB2.0 Hub, vendor 0x05e3
  addr 3: Microsoft 2.4GHz Transceiver v4.0, Microsoft
addr 1: UHCI root hub, Intel
 addr 2: Generic USB Hub, Chicony
  addr 3: PFU-65 USB Keyboard, Chicony

The receiver for my wireless mouse, which is plugged into a USB hub
(this is to fix a different problem where if the receiver is directly
plugged into the machine it stops working and FreeBSD complains that
it has disabled the USB controller!), and my Happy Hacking keyboard
which sits behind its own built-in hub.

The machine is:
% uname -a
FreeBSD tomo.jamesoff.net 7.1-RELEASE FreeBSD 7.1-RELEASE #4: Mon Jan
26 22:16:37 UTC 2009
root at tomo.jamesoff.net:/usr/obj/usr/src/sys/GENERIC  i386

The board is an ASUS P5Q3 with a Q6600 2.4GHz installed.

If there is any other information I should supply or debugging I can
do, please let me know.

/JMS