Thanks a bunch Nitin, your mail helps me connect the dots -- the thing
I was missing was the connection with ethernet_register_interface()
Cool browsing done by you !
Please do check my other mail too on the list (for frames) and it
would be great if we can drill down on that topic too.
Regards
-Prashant
On Fri, May 11, 2018 at 7:08 PM, Nitin Saxena <nitin.sax...@cavium.com> wrote:
> Hi Prashant,
>
> Hope you are doing fine.
>
> Regarding your question, I am not able to see macswap plugin in current
> master branch but I will try to explain wrt dpdk_plugin:
>
> With respect to low level device each VPP device driver registers for
>
> 1) INPUT_NODE (For Rx) VLIB_REGISTER_NODE (This you already figured out)
> 2) And Tx function via VNET_DEVICE_CLASS (), Device class like "dpdk"
> There are couple of more function pointers registered but let stick to Rx/Tx
> part.
>
> As part of startup low level plugin/driver calls
> ethernet_register_interface() which in turn calls vnet_register_interface().
>
> vnet_register_interface:
> For a particular interface like Intel 40G, init time interface node is
> created and the tx function of that node is copied from
> VNET_DEVICE_CLASS{.tx_function=<xxxx>"}. node->tx and node->output functions
> are properly initialized and node is registered.
>
> VPP stack sends packet to this low level Tx node via sw_if_index. I am
> guessing sw_if_index is determined by IPv4 routing or L2 switching.
>
> I think vnet_set_interface_output_node() is called for those interface (Tx
> path) whose DEVICE_CLASS do not provide tx_functions but I am not sure.
>
> "show vlib graph" will tell you how nodes are arranged in vpp graph.
>
> To be specific for your question
>
> next0 = hi0->output_node_next_index;
>
> output_node_next_index is the index of next node at which the current vector
> has to be copied. (Transition from one node to another along the graph)
>
> Note: All this I got through browsing code and if this information is not
> correct, I request VPP experts to correct it.
>
> Thanks,
> Nitin
>
>
> On Thursday 10 May 2018 02:19 PM, Prashant Upadhyaya wrote:
>>
>> Hi,
>>
>> I am trying to walk throught the code to see how the packet arrives
>> into the system at dpdk rx side and finally leaves it at the dpdk tx
>> side. I am using the context of the macswap sample plugin for this.
>>
>> It is clear to me that dpdk-input is a graph node and it is an 'input'
>> type graph node so it polls for the packets using dpdk functions. The
>> frame is then eventually passed to the sample plugin because the
>> sample plugin inserts itself at the right place. The sample plugin
>> queues the packets to the interface-output graph node.
>>
>> So now I check the interface-output graph node function.
>> I locate that in vpp/src/vnet/interface_output.c
>> So the dispatch function for the graph node is
>> vnet_per_buffer_interface_output
>> Here the interface-output node is queueing the packets to a next node
>> based on the following code --
>>
>> hi0 =
>> vnet_get_sup_hw_interface (vnm,
>> vnet_buffer (b0)->sw_if_index
>> [VLIB_TX]);
>>
>> next0 = hi0->output_node_next_index;
>>
>> Now I am a little lost, what is this output_node_next_index ? Which
>> graph node function is really called for really emitting the packet ?
>> Where exactly is this setup ?
>>
>> I do see that the actual dpdk tx burst function is called from
>> tx_burst_vector_internal, which itself is called from
>> dpdk_interface_tx (vpp/src/plugins/dpdk/device/device.c). But how the
>> code reaches the dpdk_interface_tx after the packets are queued from
>> interface-output graph node is not clear to me. If somebody could help
>> me connect the dots, that would be great.
>>
>> Regards
>> -Prashant
>>
>>
>>
>
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