[dpdk-dev] Broken RSS hash computation on Intel 82574L

[Avi Kivity]

On 09/01/2015 05:47 PM, Matthew Hall wrote:
> On Tue, Sep 01, 2015 at 04:37:18PM +0200, Martin Drašar wrote:
>> Dne 1.9.2015 v 15:45 De Lara Guarch, Pablo napsal(a):
>>> 82574L NIC uses em PMD, which does not support more than 1 queue.
>>> Therefore RSS is disabled in the NIC and then you cannot have RSS hashes.
>>>
>>> Thanks,
>>> Pablo
>> Hi Pablo,
>>
>> that is an interesting information. I read the rationale in em_ethdev.c
>> and I was wondering, what would have to be done to enable RSS hash
>> computation on that card. I can live with just one RX queue, but hashes
>> would help me a lot. The computer which is using those NICs is not that
>> powerful and every bit of offloaded computation counts...
>>
>> Thanks,
>> Martin
> RSS calculations are used to direct packets across multiple RX queues. With
> only one RX queue it cannot possibly increase performance by enabling it.
>

As an example, seastar uses the RSS hash computed by the NIC to select a 
core to process on, if the number of hardware queues is smaller than the 
number of cores.