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SubjectRe: [bug, bisected] pfifo_fast causes packet reordering
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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

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