Hi all,
What about the following steps:
- update the nodes so they work on the current layer (example: for all L3
nodes, the current mbuf data offset *must* be pointing to the IP header)
- define a public data structure that would be shared across nodes through priv
data, and not dynfields ? This structure would be the "internal api" (so, that
has to be tracked across dpdk releases) between nodes.
We’d need common data shared for all the nodes as well as specific data between
2 nodes.
As we get to this point, this (hopefully) will help with the node reusability.
- Update the feature arcs to leverage this well known structure, and refine the
api
- Define which part of the stack needs to be defined as a feature arc, with the
benefit of the generic API to enable/disable that feature, and which part needs
to be dynamically pluggable.
For instance, for a router, it may not make sense to define IPv4 support as a
feature arc.
So, we’d statically connect eth_input to ip_input.
Yet, lldp support is a good candidate for a feature arc: we need to configure
it per interface, and this is independent of the main graph.
WDYT?
Christophe
> On 17 Oct 2024, at 09:50, Robin Jarry <rja...@redhat.com> wrote:
>
> Hi Nitin, all,
>
> Nitin Saxena, Oct 17, 2024 at 09:03:
>> Hi Robin/David and all,
>>
>> We realized the feature arc patch series is difficult to understand as a new
>> concept. Our objectives are following with feature arc changes
>>
>> 1. Allow reusability of standard DPDK nodes (defined in lib/nodes/*) with
>> out-of-tree applications (like grout). Currently out-of-tree graph
>> applications are duplicating standard nodes but not reusing the standard
>> ones which are available. In the long term, we would like to mature
>> standard DPDK nodes with flexibility of hooking them to out-of-tree
>> application nodes.
>
> It would be ideal if the in-built nodes could be reused. When we started
> working on grout, I tried multiple approaches where I could reuse these
> nodes, but all failed. The nodes public API seems tailored for app/graph but
> does not fit well with other control plane implementations.
>
> One of the main issues I had is that the ethdev_rx and ethdev_tx nodes are
> cloned per rxq / txq associated with a graph worker. The rte_node API
> requires that every clone has a unique name. This in turn makes hot plugging
> of DPDK ports very complex, if not impossible.
>
> For example, with the in-built nodes, it is not possible to change the number
> of ports or their number of RX queues without destroying the whole graph and
> creating a new one from scratch.
>
> Also, the current implementation of "ip{4,6}-rewrite" handles writing
> ethernet header data. This would prevent it from using this node for an
> IP-in-IP tunnel interface as we did in grout.
>
> Do you think we could change the in-built nodes to enforce OSI layer
> separation of concerns? It would make them much more flexible. It may cause a
> slight drop of performance because you'd be splitting processing in two
> different nodes. But I think flexibility is more important. Otherwise, the
> in-built nodes can only be used for very specific use-cases.
>
> Finally, I would like to improve the rte_node API to allow defining and
> enforcing per-packet metadata that every node expects as input. The current
> in-built nodes rely on mbuf dynamic fields for this but this means you only
> have 9x32 bits available. And using all of these may break some drivers
> (ixgbe) that rely on dynfields to work. Have you considered using mbuf
> private data for this?
>
>>
>> 2. Flexibility to enable/disable sub-graphs per interface based on the
>> runtime configuration updates. Protocol sub-graphs can be selectively
>> enabled for few (or all interfaces) at runtime
>>
>> 3. More than one sub-graphs/features can be enabled on an interface. So a
>> packet has to follow a sequential ordering node path on worker cores.
>> Packets may need to move from one sub-graph to another sub-graph per
>> interface
>>
>> 4. Last but not least, an optimized implementation which does not (or
>> minimally) stop worker cores for any control plane runtime updates. Any
>> performance regression should also be avoided
>>
>> I am planning to create a draft presentation on feature arc which I can
>> share, when ready, to discuss. If needed, I can also plan to present that in
>> one of the DPDK community meetings. Their we can also discuss if there are
>> any alternatives of achieving above objectives
>
> Looking forward to this.
>
> Thanks!
>
