netdev - Re: [bug, bisected] pfifo_fast causes packet reordering

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Date:   Thu, 15 Mar 2018 15:30:55 -0700
From:   John Fastabend <john.fastabend@...il.com>
To:     Jakob Unterwurzacher <jakob.unterwurzacher@...obroma-systems.com>,
        Dave Taht <dave.taht@...il.com>
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        "David S. Miller" <davem@...emloft.net>,
        "linux-can@...r.kernel.org" <linux-can@...r.kernel.org>,
        Martin Elshuber <martin.elshuber@...obroma-systems.com>
Subject: Re: [bug, bisected] pfifo_fast causes packet reordering

On 03/15/2018 11:08 AM, Jakob Unterwurzacher wrote:
> On 14.03.18 05:03, John Fastabend wrote:
>> On 03/13/2018 11:35 AM, Dave Taht wrote:
>>> On Tue, Mar 13, 2018 at 11:24 AM, Jakob Unterwurzacher
>>> <jakob.unterwurzacher@...obroma-systems.com> wrote:
>>>> During stress-testing our "ucan" USB/CAN adapter SocketCAN driver on Linux
>>>> v4.16-rc4-383-ged58d66f60b3 we observed that a small fraction of packets are
>>>> delivered out-of-order.
>>>>
>>
>> Is the stress-testing tool available somewhere? What type of packets
>> are being sent?
> 
> 
> 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.

> Here is what I get:
> 
> root@...399-q7:~# ./pfifo_stress.py
> [...]
> expected ctr 0xcdc, received 0xcdd
> expected ctr 0xcde, received 0xcdc
> expected ctr 0xcdd, received 0xcde
> expected ctr 0xe3c, received 0xe3d
> expected ctr 0xe3e, received 0xe3c
> expected ctr 0xe3d, received 0xe3e
> expected ctr 0x1097, received 0x1098
> expected ctr 0x1099, received 0x1097
> expected ctr 0x1098, received 0x1099
> expected ctr 0x17c0, received 0x17c1
> expected ctr 0x17c2, received 0x17c0
> [...]
> 
> Best regards,
> Jakob