Re: Excessive interrupt time on Raspberry Pi

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

> On May 26, 2018, at 7:24 AM, Jared McNeill <jmcneill%invisible.ca@localhost> wrote:
> 
> Nick tells me the microframe scheduler has to run on the host if at least one device is connected and since you can't remove the built-in hub or ethernet from rpi, you're screwed. Raspbian kernel uses FIQ to help here..

Ah, of course.  Yah, a FIQ would help, but geez I hate doing board-specific code for generic drivers like that (mostly because it’s hard to get the software abstractions right).

> 
> 
> On Sat, 26 May 2018, Jason Thorpe wrote:
> 
>> 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
>> 
>> 

-- thorpej