I'm always confused on which to use for Packet Steering
Enabled?
Enabled All CPU's?
Whats Steering Flow?
The answer is: it depends, this is why there are selectable options... For bigger machines with plenty of cores enabled is fine, that will exclude the CPU handling the NICs interrupts and distribute the processing over the other CPUs but on a dual core CPU that is equivalent to not enabling steering at all.
The second option is relevant if the traffic actually terminates on the device in question.
I have a 4 core cpu my router is rbr50v1 so having it on enabled is fine?
I am afraid I can not say, so you will need to test it with your own traffic...
How would one test this this to determine optimal settings?
Got a MT7621 2C/4T router on a 60/30 Mb/s fibre using DHCP client mode.
Well, just test the different options and look at the outcome in two main dimensions:
a) do you achieve the expected (bidirectional) throughput, which you might not if these are set incorrectly
b) concurrently measure latency
c) also monitor cpu load on the router, especially SIRQ/softinterrupt processing per CPU
both increasing latency and not reaching the expected throughput (as is monitoring showing a CPU in constant high load of say 90% or higher) are signs of running out of CPU cycles and packet steering can, to some degree help by allowing to move CPU intensive network processing like traffic shapers to other, less loaded CPUs.
Sorry for not having an easy to follow real-world instruction here.