Linux

Introduction I read “The eXpress data path: fast programmable packet processing in the operating system kernel” 1. This article is mostly based on this paper, with some references to news articles. The popularity of eBPF/XDP can be felt from the GitHub star counts of projects using eBPF/XDP, such as BCC, bpftrace, Facebook Katran, and Cloudflare Gatebot. eBPF/XDP has a powerful advantage: it can achieve high-speed packet processing as a kernel mechanism without depending on special hardware or software....

Notes on Towards a more Scalable KVM Hypervisor presented at KVM FORUM 2018. [PATCH v8 0/4] KVM: X86: Add Paravirt TLB Shootdown Guest OSes are affected by the host OS scheduler during OS-level synchronization mechanisms such as TLB shoot down and RCU processing. Operations that would complete immediately in a bare-metal environment cannot ignore delays in a virtual environment. TLB (Translation Lookaside Buffer) is used to cache mappings between virtual memory addresses and physical memory addresses....

I read Linux Observability with BPF, so I’ll leave some notes. This month, Brendan Gregg’s BPF book is also coming out, so I’d like to read that too. Using BPF allows hooking kernel events and safely executing code BPF verifies that the code won’t destroy or crash the system Unlike kernel modules, BPF programs don’t require kernel recompilation After BPF code is verified, BPF bytecode is JIT-compiled to machine instructions BPF programs are loaded into the BPF VM by the bpf syscall Alexei Starovoitov introduced eBPF in early 2014 Old BPF only allowed 2 32-bit registers, but eBPF allows up to 10 64-bit registers In June 2014, eBPF was also extended to user space BPF program types: Can be broadly classified into tracing and networking Socket Filter: First program type to enter the kernel....

I managed to get the USB wireless LAN adapter TP-Link Archer T3U AC1300 working on a Thinkpad X1 Carbon 2015 (Fedora release 29 (Twenty Nine), linux 5.3.6-100.fc29.x86_64), so I’m documenting the procedure. # The official website didn't distribute drivers, so I used rtl88x2bu git clone https://github.com/cilynx/rtl88x2bu cd rtl88x2bu/ git rev-parse HEAD # 962cd6b1660d3dae996f0bde545f641372c28e12 VER=$(sed -n 's/\PACKAGE_VERSION="\(.*\)"/\1/p' dkms.conf) sudo rsync -rvhP ./ /usr/src/rtl88x2bu-${VER} # Move to /usr/src/<module_name>_<module_version> and manage with dkms sudo dkms add -m rtl88x2bu -v ${VER} sudo dkms build -m rtl88x2bu -v ${VER} sudo dkms install -m rtl88x2bu -v ${VER} sudo dkms status sudo modprobe 88x2bu When connecting two types of adapters (onboard adapter and TP-Link adapter) to the same network, priority is determined by metric....