IPv4 flows per queue on top of RSS for ixgbe and i40e drivers

[Stephen Hemminger]

On Wed, 5 Feb 2025 18:21:33 +0200
Pavel Vazharov <freakpv at gmail.com> wrote:

> Hi there,
> 
> We have a proxy application on top of DPDK where we use a symmetric
> RSS key to receive the packets for a given connection in both
> directions on a single queue. In addition to that, we've few IPv4
> addresses where we need to receive their traffic on particular queues.
> We use the rte flows functionality with RTE_FLOW_ACTION_TYPE_QUEUE to
> achieve that and it seemed to work with the DPDK ixgbe driver.
> However, today we tried the same application on top of DPDK i40e
> driver and this setup doesn't seem to work there. It prints the
> following errors:
> `i40e_flow_add_del_fdir_filter(): Conflict with existing flow director rules!`
> It seems that the i40e driver doesn't allow adding flow rules on top
> of the already set RSS.
> 
> Can somebody suggest a way to achieve what we need with i40e: to use a
> symmetric RSS key for most of the traffic but to redirect the traffic
> for a few specific IPv4 addresses to particular queues?
> 
> Thanks,
> Pavel.

If you are mixing RSS and rte_flow the results are not well defined.
Many drivers treat all active queues (including those used by rte_flow)
as candidates for RSS.

If you want to mix, the the safe way is:
	- don't enable RSS in the device config (rx_mode)
	- define an rte_flow rule with RTE_FLOW_ACTION_TYPE_RSS
          with a match all
	- define a rte_flow rule with RTE_FLOW_ACTION_TYPE_QUEUE
	  that matches the IP
and set rule priorities so that specific IP rule matches before
the match all.

You still maybe at risk of hardware quirks and driver incompatibilities
which is part of the problem with rte_flow.