@@ -295,6 +295,41 @@ using::
For XDP_SKB mode, use the switch "-S" instead of "-N" and all options
can be displayed with "-h", as usual.
+FAQ
+=======
+
+Q: I am not seeing any traffic on the socket. What am I doing wrong?
+
+A: When a netdev of a physical NIC is initialized, Linux usually
+ allocates one Rx and Tx queue pair per core. So on a 8 core system,
+ queue ids 0 to 7 will be allocated, one per core. In the AF_XDP
+ bind call or the xsk_socket__create libbpf function call, you
+ specify a specific queue id to bind to and it is only the traffic
+ towards that queue you are going to get on you socket. So in the
+ example above, if you bind to queue 0, you are NOT going to get any
+ traffic that is distributed to queues 1 through 7. If you are
+ lucky, you will see the traffic, but usually it will end up on one
+ of the queues you have not bound to.
+
+ There are a number of ways to solve the problem of getting the
+ traffic you want to the queue id you bound to. If you want to see
+ all the traffic, you can force the netdev to only have 1 queue, queue
+ id 0, and then bind to queue 0. You can use ethtool to do this::
+
+ sudo ethtool -L <interface> combined 1
+
+ If you want to only see part of the traffic, you can program the
+ NIC through ethtool to filter out your traffic to a single queue id
+ that you can bind your XDP socket to. Here is one example in which
+ UDP traffic to and from port 4242 are sent to queue 2::
+
+ sudo ethtool -N <interface> rx-flow-hash udp4 fn
+ sudo ethtool -N <interface> flow-type udp4 src-port 4242 dst-port \
+ 4242 action 2
+
+ A number of other ways are possible all up to the capabilitites of
+ the NIC you have.
+
Credits
=======
@@ -309,4 +344,3 @@ Credits
- Michael S. Tsirkin
- Qi Z Zhang
- Willem de Bruijn
-
Added an FAQ section in Documentation/networking/af_xdp.rst to help first time users with common problems. As problems are getting identified, entries will be added to the FAQ. Signed-off-by: Magnus Karlsson <magnus.karlsson@intel.com> --- Documentation/networking/af_xdp.rst | 36 +++++++++++++++++++++++++++++++++++- 1 file changed, 35 insertions(+), 1 deletion(-)