Re: [bug, bisected] pfifo_fast causes packet reordering

[Jakob Unterwurzacher <jakob.unterwurzacher@theobroma-systems.com>]

On 15.03.18 23:30, John Fastabend wrote:
>> I have reproduced it using two USB network cards connected to each other. The test tool sends UDP packets containing a counter and listens on the other interface, it is available at
>> https://github.com/jakob-tsd/pfifo_stress/blob/master/pfifo_stress.py
>>
> 
> Great thanks, can you also run this with taskset to bind to
> a single CPU,
> 
>   # taskset 0x1 ./pifof_stress.py
> 
> And let me know if you still see the OOO.

Interesting. Looks like it depends on which core it runs on. CPU0 is 
clean, CPU1 is not.

Clean:	taskset --cpu-list 0 ./pfifo_stress.py

Broken:	taskset --cpu-list 1 ./pfifo_stress.py

Maybe related: CPU0 is where USB interrupts are handled:

> root@rk3399-q7:~# cat /proc/interrupts           
>            CPU0       CPU1       CPU2       CPU3       CPU4       CPU5
> 217:    2175353          0          0          0          0          0     GICv3 142 Level     xhci-hcd:usb5
Thanks,
Jakob