[PATCH v4 1/2] examples/l3fwd: relax RSS requirement with option

[Stephen Hemminger]

On Mon, 13 Nov 2023 08:34:47 -0800
Stephen Hemminger <stephen at networkplumber.org> wrote:

> On Mon, 13 Nov 2023 16:02:54 +0000
> Trevor Tao <taozj888 at 163.com> wrote:
> 
> > Now the port Rx mq_mode had been set to RTE_ETH_MQ_RX_RSS
> > by default, but some hw and/or virtual interface does not
> > support the RSS and offload mode presupposed, e.g., some
> > virtio interfaces in the cloud don't support
> > RSS and the error msg may like:
> > 
> > virtio_dev_configure(): RSS support requested but not supported by
> > the device
> > Port0 dev_configure = -95
> > 
> > So to enable the l3fwd running in that environment, the Rx mode requirement
> > can be relaxed to reflect the hardware feature reality here, and the l3fwd
> > can run smoothly then.
> > 
> > An option named "disable-rss" is added to disable the RX RSS explicitly,
> > and it's disabled by default.
> > 
> > Signed-off-by: Trevor Tao <taozj888 at 163.com>  
> 
> Why is running with > 1 rx queue and RSS disabled useful?
> What happens is all packets arrive on 1st queue and you burn a thread
> polling an always empty queue.
> 
> I would prefer not adding yet another command line option and
> just "do the right thing". If number of rx queues > 1, check that device
> supports RSS before using it. If device does not support RSS give
> an error and exit.

Something like this maybe:
diff --git a/examples/l3fwd/main.c b/examples/l3fwd/main.c
index 6063eb139900..c747ef8aadfb 100644
--- a/examples/l3fwd/main.c
+++ b/examples/l3fwd/main.c
@@ -1257,8 +1257,15 @@ l3fwd_poll_resource_setup(void)
 		local_port_conf.rx_adv_conf.rss_conf.rss_hf &=
 			dev_info.flow_type_rss_offloads;
 
-		if (dev_info.max_rx_queues == 1)
+		if (nb_rx_queue > dev_info.max_rx_queues)
+			rte_exit(EXIT_FAILURE, "Port %u only supports %u queues\n",
+				 portid, dev_info.max_rx_queues);
+
+		if (nb_rx_queue == 1)
 			local_port_conf.rxmode.mq_mode = RTE_ETH_MQ_RX_NONE;
+		else if (!(dev_info.rx_offload_capa & RTE_ETH_RX_OFFLOAD_RSS_HASH))
+			rte_exit(EXIT_FAILURE, "Port %u does not support RSS but %u queues requested\n",
+				 portid, nb_rx_queue);
 
 		if (local_port_conf.rx_adv_conf.rss_conf.rss_hf !=
 				port_conf.rx_adv_conf.rss_conf.rss_hf) {