programming | rvdp.org

programming:

The End of Moore's Law

Tue, Mar 19, 2019 - 945 Words - 5 minutes

For about half a century we have been living in a world where the speed of computers grew at an exponential rate. This is known as Moore's law, which is actually an observation of Gordon Moore that the number of transistors in an integrated circuit doubled approximately every two years. But today, that rate has almost levelled off. And Moore's law is not the only exponential that has come to its end. The same is true for Dennard scaling. In networking we are also hitting limits. We have reached the Shannon limit in optical communication. And in network ASIC design we reached the limit of serial bandwidth I/O. The next sections explore the current challenges and the final sections describe R&D that is exploring ways to overcome these challenges.

Cuckoo Hashing

Mon, Mar 11, 2019 - 1372 Words - 7 minutes

Hash tables play an important role in routers and switches because lookups need to done in constant time. Minimal size packets (64 bytes on Ethernet) on a 100 Gb/s link arrive at a rate of once every 6.7 ns. All packet handling (lookup, rewrite of next hop, updating CRC, etc.) must be done within that time. Hash tables satisfy that requirement and they are typically used for exact match lookups, such as the MAC addressing forwarding table or host IP route lookups.

Network Programming with XDP and BPF

Mon, Mar 11, 2019 - 523 Words - 3 minutes

The BPF framework can be used to load programs into the Linux kernel at runtime. It can be used for both tracing and for network programming. The BPF code runs in a virtual machine inside the kernel. BPF has a small (around 100 opcodes) RISC-like 64-bit Instruction Set Architecture (ISA). It uses 11 64-bit registers and a 512-byte stack. BPF programs can be written in various languages (C, Go, Rust, etc.) and compiled with clang/LLVM to BPF bytecode.