From 0f4a9b7d4ecbac191052cb80b84a46471fd30d80 Mon Sep 17 00:00:00 2001 From: Magnus Karlsson Date: Thu, 21 Feb 2019 10:21:28 +0100 Subject: xsk: add FAQ to facilitate for first time users 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 Signed-off-by: Daniel Borkmann --- Documentation/networking/af_xdp.rst | 36 +++++++++++++++++++++++++++++++++++- 1 file changed, 35 insertions(+), 1 deletion(-) (limited to 'Documentation') diff --git a/Documentation/networking/af_xdp.rst b/Documentation/networking/af_xdp.rst index 4ae4f9d8f8fe..e14d7d40fc75 100644 --- a/Documentation/networking/af_xdp.rst +++ b/Documentation/networking/af_xdp.rst @@ -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 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 rx-flow-hash udp4 fn + sudo ethtool -N 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 - -- cgit v1.2.3