diff options
Diffstat (limited to 'Documentation/networking')
| -rw-r--r-- | Documentation/networking/af_xdp.rst | 36 | ||||
| -rw-r--r-- | Documentation/networking/filter.txt | 2 |
2 files changed, 36 insertions, 2 deletions
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 <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 - diff --git a/Documentation/networking/filter.txt b/Documentation/networking/filter.txt index b5e060edfc38..319e5e041f38 100644 --- a/Documentation/networking/filter.txt +++ b/Documentation/networking/filter.txt @@ -829,7 +829,7 @@ tracing filters may do to maintain counters of events, for example. Register R9 is not used by socket filters either, but more complex filters may be running out of registers and would have to resort to spill/fill to stack. -Internal BPF can used as generic assembler for last step performance +Internal BPF can be used as a generic assembler for last step performance optimizations, socket filters and seccomp are using it as assembler. Tracing filters may use it as assembler to generate code from kernel. In kernel usage may not be bounded by security considerations, since generated internal BPF code |