[dpdk-dev] supported packet types

Olivier MATZ olivier.matz at 6wind.com
Thu Jun 16 09:49:23 CEST 2016

Hi Konstantin,

On 06/15/2016 04:08 PM, Ananyev, Konstantin wrote:
> Hi Olivier,
>> Hi Konstantin,
>> On 04/29/2016 06:03 PM, Ananyev, Konstantin wrote:
>>>> The following commit introduces a function to list the supported
>>>> packet types of a device:
>>>>    http://dpdk.org/browse/dpdk/commit/?id=78a38edf66
>>>> I would like to know what does "supported" precisely mean.
>>>> Is it:
>>>> 1/ - if a ptype is marked as supported, the driver MUST set
>>>>       this ptype if the packet matches the format described in rte_mbuf.h
>>>>     -> if the ptype is not recognized, the application is sure
>>>>        that the packet is not one of the supported ptype
>>>>     -> but this is difficult to take advantage of this inside an
>>>>        application that supports several different ports model
>>>>        that do not support the same packet types
>>>> 2/ - if a ptype is marked as supported, the driver CAN set
>>>>       the ptype if the packet matches the format described in rte_mbuf.h
>>>>     -> if a ptype is not recognized, the application does a software
>>>>        fallback
>>>>     -> in this case, it would useless to have the get_supported_ptype()
>>>> Can you confirm if the PMDs and l3fwd (the only user) expect 1/
>>>> or 2/ ?
>>> 1)
>>>> Can you elaborate on the advantages of having this API?
>>> Application can rely on information provided by PMD avoid parsing packet manually to recognise it's pytpe.
>>>> And a supplementary question: if a ptype is not marked as supported,
>>>> is it forbidden for a driver to set this ptype anyway?
>>> I suppose it is not forbidden, but there is no guarantee from PMD that it
>>> would be able to recognise that ptype.
>>> Konstantin
>>>> Because we can
>>>> imagine a hardware that can only recognize packets in some conditions
>>>> (ex: can recognize IPv4 if there is no vlan).
>>>> I think properly defining the meaning of "supported" is mandatory
>>>> to have an application beeing able to use this feature, and avoid
>>>> PMDs to behave differently because the API is unclear (like we've
>>>> already seen for other features).
>> Back on this. I've made some tests with ixgbe, and I'm afraid it
>> will be difficult to ensure that when a ptype is advertised, it will
>> always be set in the mbuf, whatever the layers below. Here are some
>> examples:
> 1)
>> - double vlans
>> Ether(type=0x88A8)/Dot1Q(vlan=0x666)/Dot1Q(vlan=0x666)/IP()/UDP()/Raw("x"*32)
>>    ixgbe advertises RTE_PTYPE_ETHER in supported ptypes
>>    returned ptype: RTE_PTYPE_UNKNOWN
>>    should be: L2_ETHER
>>    (this works with any unknown ethtype)
> 2)
>> - ip6 in ip6 tunnel
>>    ixgbe advertises RTE_PTYPE_TUNNEL_IP in supported ptypes
>>    Ether()/IPv6()/IPv6()/UDP()/Raw("x"*32)
>>    returned ptype: L2_ETHER L3_IPV6
> 3)
>> - ip options
>>    Ether()/IP(options=IPOption('\x83\x03\x10'))/UDP()/Raw("x"*32)
>>    returned ptype: RTE_PTYPE_UNKNOWN
>>    should be: L2_ETHER L3_IPV4_EXT L4_UDP
> 4)
>> - ip inside ip with options
>>    Ether()/IP(options=IPOption('\x83\x03\x10'))/IP()/UDP()/Raw("x"*32)
>>    returned ptype: L2_ETHER L3_IPV4_EXT
> I am marked your test-cases with numbers to simplify referencing to them.
> 1) & 3) - I believe the reason is a bug in our ptype code inside ixgbe PMD :(
> I submitted a patch:
> http://dpdk.org/dev/patchwork/patch/13820/
> Could you give it a try?
> I think it should fix these issues.

1) works, I now have L2_ETHER
3) works, I now have L2_ETHER L3_IPV4_EXT L4_UDP

I'll answer to the other thread to so it appears on patchwork.

> 2) & 4) - unfortunately ixgbe HW supports only ipv4->ipv6 tunneling.
> All other combinations are not supported.
> Right now I didn't decide what is a best way to address this problem.
> Two thoughts  I have right now:
> - either  remove tunnelling recognition (RTE_PTYPE_TUNNEL_IP and RTE_PTYPE_INNER_*)
> from supported ptypes in ixgbe_dev_supported_ptypes_get().
> But that looks a bit ugly, again wuld probably be required for VXLAN/GRE and might be other
> tunnelling protocols in future.
> So don't really like any of them.
> If you have any better idea, please shout.

No better idea. I'd say the first one is better because it does not
require to change the ptypes definition.

Another idea (but probably worst) is to do a software fallback
in the PMD, but I don't believe the PMD is the proper place for that.

>> I'm sure we can find more examples that do not return the expected
>> result, knowing that ixgbe is probably one of the most complete
>> driver in dpdk. I'm afraid of the behavior for other PMDs :)
> It is in general, but not for that particular feature :(
>> That's why I think the get_supported_ptypes() function, as of today,
>> is useless for an application.
> Hmm for me right now it looks more like incorrect implementation.


Do you mind if I send a patch to precise a bit what
supported ptype should return? I mean highlighting the fact
that it should return the ptypes that are _always_ recognized,
not the ptypes that _can_ be recognized. But it does not prevent
a PMD to set a ptype that is not in the supported list when
it knows it is correct.

>> I suggest instead to set the ptype
>> in an opportunistic fashion instead:
>> - if the driver/hw knows the ptype, set it
>> - else, set it to unknown
> That's what PMD does now... and I don't think it can do much more -
> only interpret information provided by the HW in a proper way.
> Probably I misunderstood you here...

My suggestion was to remove get_supported_ptypes an set the ptype in
mbuf when the pmd recognize a type.

But we could also keep get_supported_ptypes() for ptypes that will
always be recognized, allowing a PMD to set any other ptype if it
is recognized. This is probably what we have today in some PMDs, I
think it just requires some clarification.

>> What do you think?
>> By the way, I'm working on a software implementation that return a
>> packet_type from a mbuf. I may need it for virtio offload, but before
>> that, I think it could be useful for debug purposes. I'll submit a
>> patchset for this in the coming days.
> Would be interesting to see.
> I had to develop something similar - so my one is not totally generic,
> as that app is only interested in L3/L4 types (no tunnelling, etc.).

I'll send it soon to the ML.


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