On Tue, Jul 22, 2025 at 07:08:15AM -0700, Stephen Hemminger wrote: > On Tue, 15 Jul 2025 12:53:30 +0000 > Bruce Richardson <bruce.richard...@intel.com> wrote: > > > For testing purposes it can be desirable to enable RSS even when only a > > single queue per port is in use. Add an "enable-rss" flag to testpmd to > > match the existing "disable-rss" flag. > > > > Signed-off-by: Bruce Richardson <bruce.richard...@intel.com> > > --- > > Not sure about this. > It makes no sense to have RSS enabled with single queue. > Maybe you want the hash but no steering? >
Yep, that is one scenario we have seen it being used in the past. Also, it's a useful "harmless" offload that can be used to check that the offload paths in the NIC are working correctly. > But the DPDK RSS flag doesn't require driver to produce HASH. > > I would even argue that ethdev layer should warn application > trying to do single queue and RSS. I definitely don't think it should warn about it, because there are definitely usecases where you may want it enabled for single-queue case, e.g. when using NIC that provides the hash. However, it should not be the default, which is why this is a separate enabling flag. Another reason it's good to have it, is to ensure that when testing single queue vs multi-queue setups, we can test with the exact same configuration between those two scenarios. Without the ability to enable RSS, then multi-queue will always have a different NIC configuration to single queue. In the case of some of our drivers, for example, the lack of any offloads such as RSS causes a different faster RX path to be chosen in the single-queue case, since no packet flags need to be handled. /Bruce
