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

From: Paolo Abeni <[email-masked]>
Date: Mon, 19 Mar 2018 13:32:30 +0100

Hi,

On Fri, 2018-03-16 at 11:26 +0100, 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

Is not clear to me if you can reproduce the bug with the vanilla
kernel, or if  you need some out-of-tree nic driver. Can you please
clarify which NIC/driver are you using?

Thanks,

Paolo