Re: Understanding Flow API action RSS

[Stephen Hemminger <stephen@networkplumber.org>]

On Tue, 04 Jan 2022 13:41:55 +0100
Thomas Monjalon <thomas@monjalon.net> wrote:

> +Cc Ori Kam, rte_flow maintainer
> 
> 29/12/2021 15:34, Ivan Malov:
> > Hi all,
> > 
> > In 'rte_flow.h', there is 'struct rte_flow_action_rss'. In it, 'queue' is
> > to provide "Queue indices to use". But it is unclear whether the order of 
> > elements is meaningful or not. Does that matter? Can queue indices repeat?

The order probably doesn't matter, it is like the RSS indirection table.

    rx queue = RSS_indirection_table[ RSS_hash_value % RSS_indirection_table_size ]

So you could play with multiple queues matching same hash value, but that
would be uncommon.

> > An ethdev may have "global" RSS setting with an indirection table of some
> > fixed size (say, 512). In what comes to flow rules, does that size matter?

Global RSS is only used if the incoming packet does not match any rte_flow
action. If there is a a RTE_FLOW_ACTION_TYPE_QUEUE or RTE_FLOW_ACTION_TYPE_RSS
these take precedence.

> > When the user selects 'RTE_ETH_HASH_FUNCTION_DEFAULT' in action RSS, does
> > that allow the PMD to configure an arbitrary, non-Toeplitz hash algorithm?

No the default is always Toeplitz.  This goes back to the original definition
of RSS which is in Microsoft NDIS and uses Toeplitz. 

DPDK should have more examples of using rte_flow, I have some samples
but they aren't that useful.