Excessive interrupt time on Raspberry Pi

[Jason Thorpe <thorpej%me.com@localhost>]

So, my Raspberry Pi is sitting completely idle other than an ssh session (over USB-connected-WiFi) and an instance of top(1) running:

load averages:  0.02,  0.02,  0.00;               up 0+08:19:41        06:10:44
22 processes: 21 sleeping, 1 on CPU
CPU states:  0.0% user,  0.0% nice,  0.0% system,  4.8% interrupt, 95.2% idle
Memory: 191M Act, 584K Inact, 12M Wired, 13M Exec, 170M File, 175M Free
Swap: 128M Total, 128M Free

That interrupt time is **insane**.

Turns out it’s the USB:

bcm2835 pic timer3       3115038   99
bcm2835 pic Mailbox         1039    0
bcm2835 pic uart            7797    0
bcm2835 pic emmc           70272    2
bcm2835 pic dma0           18396    0
bcm2835 pic usb        251638013 8075
bcm2835 pic Doorbell0          4    0
Total                  254850559 8178

If I unplug my urtwn WiFi and reboot, the situation isn’t any better; with nothing plugged into the USB ports, I’m still getting ~8K interrupts per second from USB:

interrupt               total rate
bcm2835 pic timer3       9795  104
bcm2835 pic Mailbox         4    0
bcm2835 pic uart         3430   36
bcm2835 pic emmc        38303  407
bcm2835 pic dma0        12589  133
bcm2835 pic usb        770580 8197
bcm2835 pic Doorbell0       4    0
Total                  834705 8879

Do other platforms have use the DesignWare USB controller have a similar problem?

-- thorpej