How to install, build and use XDP related packages

PAGE UNDER CONSTRUCTION

Getting Started

XDP stands for eXpress Data Path, and eBPF or BPF stands for extended Berkeley Data Filter

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 repository which has compatible versions of both. The difficulty is that the xdp-tools repo's 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.

Future advancements/versions in XDP/BPF will mean that this will need to be redone at some point, so I make note of what was done. Be warned that changes in this code are often checked in which break the build (due to, Ahem!, things like putting headers in different directories and not changing the makefile, Ahem!).

Following are links to a few good places to start learning:

• The best place to learn to program is the tutorial:

https://github.com/xdp-project/xdp-tutorial

• Forked GitHub repo of XDP/BPF code (with changes to makefiles for libbpf installation):

https://github.com/JeffersonLab/xdp-tools

• Original GitHub repo of XDP/BPF code:

https://github.com/xdp-project/xdp-tools

• Very short beginner's guide:

https://dev.to/satrobit/absolute-beginner-s-guide-to-bcc-xdp-and-ebpf-47oi

Get and install the XPD/BPF related files

export DESTDIR=<installation dir>
export PREFIX=""
git clone --recurse-submodules https://github.com/JeffersonLab/xdp-tools.git
cd xdp-tools

Before this code can be compiled, you must follow the proper setup procedure.

Setup instructions are at given in the tutorial, https://github.com/xdp-project/xdp-tutorial. Go to the setup_dependencies.org link at

https://github.com/xdp-project/xdp-tutorial/blob/master/setup_dependencies.org

This tells us 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)

// xdl-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

// to install
export DESTDIR=<install dir>
export LIBDIR=lib
export HDRDIR=include
export MANDIR=share
export SBINDIR=bin
export SCRIPTSDIR=scripts
make install

Get and install EJFAT's XDP related files

Go through the XDP tutorial & how to change it into EJFAT's XDP repo

git clone https://github.com/JeffersonLab/ejfat-xdp.git
cd ejfat-xdp
mkdir build
cd build
cmake ..
make install

Getting ready to use XDP sockets

• Each ejfat node has a Mellanox ConnectX-6 Dx NIC which can handle 2x100Gbps or 1x200Gbps.
• 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

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

// send all UDP IPv4 packets to queue 0
sudo ethtool -N enp193s0f1np1 flow-type udp4 action 0

// Show all flow rules
sudo ethtool -u enp193s0f1np1

// Delete rule (rule numbers seen with above command)
sudo ethtool -N enp193s0f1np1 delete <rule #>

// NOT NEEDED. Put all incoming packets into 1 queue (perhaps this can be changed later)
sudo ethtool -L enp193s0f1np1 combined 1

// To undo the above:
sudo ethtool -L enp193s0f1np1 combined 63

// 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