lightman2

Latency numbers every programmer should know

L1 cache reference ......................... 0.5 ns
Branch mispredict ............................ 5 ns
L2 cache reference ........................... 7 ns
Mutex lock/unlock ........................... 25 ns
Main memory reference ...................... 100 ns             
Compress 1K bytes with Zippy ............. 3,000 ns  =   3 µs
Send 2K bytes over 1 Gbps network ....... 20,000 ns  =  20 µs
SSD random read ........................ 150,000 ns  = 150 µs

Read 1 MB sequentially from memory ..... 250,000 ns = 250 µs

VideoCarp

Lexing for beginners

This is a guide that should teach you how to perform basic lexing in a functional programing language.
Everything was written in Elixir, but you should be able to follow it if you are using any functional programming language.
Or even an imperative programming language like Python, C or Java.\

What is lexing?

The first question you should ask yourself is, what is lexing? It's the same as tokenising, scanning or lexical analysis.
That might not help you if you haven't heard of these either. Put simply, lexing is the process of breaking down a string
into meaningful units, indepdendent of context. What a lexer will do is make the following happen:

xianmin

clowwindy设计Shadowsocks的思路分析以及设计理念

鄙人不才，尝试站在原作者clowwindy的角度，来分析一下原版协议的设计思路和理念。 没参与过最初开发，不过设计了AEAD这个协议。读了一些资料，评论。

在 7:58 PM, 31 Aug 2015 作者发了这么一段话，我很好奇其中的指代内容，遂有本文。

眼睁睁看着一群人把一个东西搞错然后朝着错误的方向走了。不过懒得管了 =。=

jboner

Latency Comparison Numbers (~2012)
----------------------------------
L1 cache reference                           0.5 ns
Branch mispredict                            5   ns
L2 cache reference                           7   ns                      14x L1 cache
Mutex lock/unlock                           25   ns
Main memory reference                      100   ns                      20x L2 cache, 200x L1 cache
Compress 1K bytes with Zippy             3,000   ns        3 us
Send 1K bytes over 1 Gbps network       10,000   ns       10 us
Read 4K randomly from SSD*             150,000   ns      150 us          ~1GB/sec SSD