[dpdk-dev] [RFC] Generic flow director/filtering/classification API

[Adrien Mazarguil]

Hi Sugesh,

I do not have much to add, please see below.

On Thu, Jul 21, 2016 at 11:06:52AM +0000, Chandran, Sugesh wrote:
[...]
> > > RSS hashing support :- Just to confirm, the RSS flow action allows
> > > application to decide the header fields to produce the hash. This
> > > gives programmability on load sharing across different queues. The
> > > application can program the NIC to calculate the RSS hash only using
> > > mac or mac+ ip or ip only using this.
> > 
> > I'd say yes but from your summary, I'm not sure we share the same idea of
> > what the RSS action is supposed to do, so here is mine.
> > 
> > Like all flow rules, the pattern part of the RSS action only filters the packets
> > on which the action will be performed.
> > 
> > The rss_conf parameter (struct rte_eth_rss_conf) only provides a key and a
> > RSS hash function to use (ETH_RSS_IPV4, ETH_RSS_NONFRAG_IPV6_UDP,
> > etc).
> > 
> > Nothing prevents the RSS hash function from being applied to protocol
> > headers which are not necessarily present in the flow rule pattern. These are
> > two independent things, e.g. you could have a pattern matching IPv4 packets
> > yet perform RSS hashing only on UDP headers.
> > 
> > Finally, the RSS action configuration only affects packets coming from this
> > flow rule. It is not performed on the device globally so packets which are not
> > matched are not affected by RSS processing. As a result it might not be
> > possible to configure two flow rules specifying incompatible RSS actions
> > simultaneously if the underlying device supports only a single global RSS
> > context.
> > 
> [Sugesh] thank you for the explanation. This means I can have a rule that matches on
> Every incoming packets(all field wild card rule) and does RSS hash on selected fields,
> MAC only, IP only or IP & MAC?

Yes, I guess it could even replace the current method for configuring RSS on
a device in a more versatile fashion, but this is a topic for another
debate.

Let's implement this API first!

> This can be useful to do a packet lookup in software by just using
> Only hash. 

Not sure to fully understand your idea, but I'm positive it could be done
somehow :)

-- 
Adrien Mazarguil
6WIND