Re: c_can: wrong frame order reception

[Oliver Hartkopp <socketcan@hartkopp.net>]

Hi Wouter,



On 10/22/2015 11:50 AM, wouter van herpen wrote:
>> you can try to use the SMP-affinity to pin the innterrupt to a specific CPU:
>>
>> 	https://www.kernel.org/doc/Documentation/IRQ-affinity.txt
>>
>> But we're currently also checking the usability of receive packet steering 
>> (RPS) on SMP systems. Please check
>>
>> 	http://marc.info/?l=linux-can&m=144251788500555&w=2
>>
>> whether just using
>>
>> 	echo f > /sys/class/net/can0/queues/rx-0/rps_cpus
>>
>> helps in you case or whether you need to set the skb hash which is suggested 
>> there too.
>>
>>
> 
> Hi Oliver,
> 
> I have tried SMP affinity, in combination with adjusting
> /sys/class/net/can0/queues/rx-0/rps_cpus. These changes did not solve the
> out of order reception.
> Also adding skb_set_hash(skb, dev->ifindex, PKT_HASH_TYPE_L2); did not make
> a difference.

That's pretty bad!

> 
> Do you have any other suggestions?

No. Indeed setting an interrupt with SMP affinity to a single CPU is already
the 'strongest' tool I know.

Did you also try SMP affinity without changing the RPS settings?

> 
> I have also done some testing with the pch_can driver. I noticed there the
> out of order receptions are less frequent. Using the pch_can driver, OOO
> reception only occurs if we stress the CPU over e.g. UART.
> Using c_can driver, the OOO replies occur more often.

@Marc: Both drivers (c_can/pch_can) use NAPI. Would it make sense to convert
e.g. the c_can driver to non-NAPI for a test?

Regards,
Oliver