[ovs-dev] Is this an issue for DPDK vhost rss?

[Dongjun]

On 2015/6/10 23:34, Gray, Mark D wrote:
>>
>>
>> On 10/06/2015 12:48, "Gray, Mark D" <mark.d.gray at intel.com> wrote:
>>> The vhost port won't generate an RSS hash because it is a virtual NIC.
>>>
>>>> It doesn't cause a problem, just make the pkt fall into a slow path,
>>>> should we
>>>> fix it?
>> Thanks for investigating this.  We should definitely fix it.
>>
>>>> The flag ol_flags may be useful for OVS or let DPDK fix this in vhost
>>>> rcv.
>>>
>>>
>>> How do you propose that this would work? The RSS would still have to be
>>>
>>> generated in software.
>>>
>> A simple solution would be to reset the RSS hash inside
>> netdev_dpdk_vhost_rxq_recv().  Other netdev providers that do not
>> support reading the RSS hash (netdev-linux, netdev-bsd) call
>> dp_packet_set_rss_hash(pkt, 0) on every received packet.
> I thought Dongjun was suggesting that we should generate a hash? I agree that
> it should be reset on every received packet. I upstreamed something similar for
> dpdkr ports. The proposal above seems good to me.
Sorry for my vague expression, Mark. Resetting RSS on every received 
packet is good enough to me.
Could rte_vhost_dequeue_burst() do this resetting?  Doing the same 
thing, seems that netdev_dpdk_vhost_rxq_recv() needs an additional loop 
but rte_vhost_dequeue_burst() need not.
>> This would probably have a small impact on performance, but it's better than
>> trashing the exact match cache.
>>
>> I don't believe there's anything that DPDK can do here (like resetting the
>> hash when the packet is freed), but please correct me if I'm wrong.
>>
>> Thoughts?
>>
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