Subject: Re: [bug, bisected] pfifo_fast causes packet reordering

From: Alexander Stein <[email-masked]>
Date: Mon, 19 Mar 2018 07:07:05 +0100

On Friday, March 16, 2018, 11:26:47 AM CET Jakob Unterwurzacher wrote:
> 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

This reminds me somewhat of this thread: https://marc.info/?l=linux-can&m=148007442317274&w=2

Best regards,
Alexander