How to install, build and use XDP related packages
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PAGE UNDER CONSTRUCTION
Getting Started
- XDP stands for eXpress Data Path, and eBPF or BPF stands for extended Berkeley Data Filter
- Following are links to a few good places to start learning to program with XDP sockets:
- The best place to learn to program is the tutorial:
- There are 2 main libraries that are needed to use XDP sockets: the libxdp library and libbpf library upon which it depends. Although one can load the 2 from separate packages, that is not recommended as this software is changing so quickly that you'll need versions of the 2 which are compatible. I believe the best option is to use the xdp-tools GitHub repository which has compatible versions of both. The difficulty is that the xdp-tools makefiles are not setup to install libbpf so some custom changes (quite minimal) are needed to be able to do this. For stability's sake I have forked the repo and made all the necessary modifications.
Links
- Future advancements/versions in XDP/BPF will mean that this will need to be redone at some point, so here is a note of what was done to make things compile and install:
- Following are links to the xdp-tools repos:
Get the GitHub repo
export PREFIX="" git clone --recurse-submodules https://github.com/JeffersonLab/xdp-tools.git cd xdp-tools
Host Dependencies
- Before this code can be compiled, you must follow the proper setup procedure to address its dependencies.
- Setup instructions are at given in the tutorial, XDP tutorial.
- Go to the setup_dependencies.org link at Setup Dependencies
- However, if you want to avoid wading through that, it boils down to:
// (to get bpftool) sudo apt install linux-tools-common linux-tools-generic // to get this to build sudo apt install linux-tools-5.15.0-87-generic sudo apt install clang llvm libpcap-dev build-essential sudo apt install linux-headers-$(uname -r) // xdp-tools needs emacs sudo apt install emacs // you will need to use clang 11 for this to work so install and set commands to this version sudo apt install clang-11 clang-format-11 sudo update-alternatives --install /usr/bin/clang clang /usr/bin/clang-11 100 sudo update-alternatives --install /usr/bin/clang++ clang++ /usr/bin/clang++-11 100 sudo update-alternatives --install /usr/bin/clang-format clang-format /usr/bin/clang-format-11 100 sudo update-alternatives --install /usr/bin/llc llc /usr/bin/llc-11 100 // check to see if this worked by doing ls -al /usr/bin/clang* ls -al /etc/alternatives/clang* ls -al /usr/bin/llc* ls -al /etc/alternatives/llc* // now one can do ./configure make // for installation // make sure there is an ending slash "/" on your install dir !! export DESTDIR=<install dir>/ export LIBDIR=lib export HDRDIR=include export MANDIR=share export SBINDIR=bin export SCRIPTSDIR=scripts make install
- The above installation will make and install the xdp-loader program into <install dir>/bin.
- It can be used (see below) to both load/unload programs and query what programs have been loaded.
Getting ready to use XDP sockets
- Each ejfat node has a Mellanox ConnectX-6 Dx NIC which can handle 2x100Gbps or 1x200Gbps.
- The interface name corresponding to this card is enp193s0f1np1. If yours is different, substitute it.
- Avoid running XDP code in the skb (generic) mode in which the linux stack is NOT bypassed.
- Use the XDP native mode in which the linux network stack is bypassed by placing special code in the kernel's NIC driver.
- To do this, the NIC's MTU must not be larger than 1 linux page minus some headers.
- On the ejfat nodes the max MTU which still allows native mode is 3498.
sudo ifconfig enp193s0f1np1 mtu 3498
NIC queues
- Now a note on how recent linux NIC drivers use multiple queues to hold incoming packets (for details see NIC Queues).
- Contemporary NICs support multiple receive and transmit descriptor queues. On reception, a NIC can send different packets to different queues to distribute processing among CPUs. The NIC distributes packets by typically applying a 4-tuple hash over IP addresses and TCP ports of a packet. In the case of efjat nodes, there are a max of 63 queues even though there are 128 cores.
- The indirection table of the NIC, which resolves a specific queue by a hash, is programmed by the driver at initialization. The default mapping is to distribute the queues evenly in the table, but the indirection table can be retrieved and modified at runtime using ethtool commands (--show-rxfh-indir and --set-rxfh-indir).
- So to see which queue a hash entry maps to by default:
// look at the default mapping of hash keys to queues sudo ethtool --show-rxfh-indir enp193s0f1np1
- You'll see an even spread of keys over the 63 queues. Now, funnel all the incoming packets into 1 queue (queue #0) so that 1 socket can receive all packets and redo the above command:
// send all UDP IPv4 packets to queue 0 sudo ethtool -N enp193s0f1np1 flow-type udp4 action 0 // look at the new mapping sudo ethtool --show-rxfh-indir enp193s0f1np1
- Here is an alternative way to put everything onto queue 0:
sudo ethtool -L enp193s0f1np1 combined 1 // Check status of combining queues sudo ethtool -L enp193s0f1np1 // Undo this with sudo ethtool -L enp193s0f1np1 combined 63
- With multiple data sources, each destined for a separate socket, multiple rules can be setup.
- If we have 2 sockets for example, with packets destined for ports 17750 and 18000, then following could be done to send port 17750 traffic to queue 0, and the 18000 traffic to queue 1:
// send port 17750 UDP IPv4 packets to queue 0 sudo ethtool -N enp193s0f1np1 flow-type udp4 dst-port 17750 action 0 // send port 18000 UDP IPv4 packets to queue 1 sudo ethtool -N enp193s0f1np1 flow-type udp4 dst-port 18000 action 1
- Here are a couple of commands to administer such rules:
// Show all flow rules sudo ethtool -u enp193s0f1np1 // Delete rule (rule numbers seen with above command) sudo ethtool -N enp193s0f1np1 delete <rule #>
git clone https://github.com/JeffersonLab/ejfat-xdp.git cd ejfat-xdp mkdir build cd build cmake .. make install
- Loading our special code into the NIC driver can be done in a number of different ways.
- This is one way which works. The code was compiled in the ejfat-xdp repo and stored in
- /daqfs/ersap/ejfat-xdp/build/bin/af_ejfat_kern.o
// Load the kernel NIC driver code sudo <xdp_install_dir>/bin/xdp-loader load -m native enp193s0f1np1 xdp_carl_kern.o // Check the NIC to see if code really loaded and in what mode sudo /daqfs/xdp/xdp-tools/xdp-loader/xdp-loader status // Remove everything just loaded sudo /daqfs/xdp/xdp-tools/xdp-loader/xdp-loader unload enp193s0f1np1 --all //Now run a program that receives packets: /daqfs/ersap/ejfat-xdp/build/bin/af_xdp_ejfat_user