tianying484

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

##ss-redir 的 iptables 配置(透明代理)

透明代理指对客户端透明，客户端不需要进行任何设置就使用了网管设置的代理规则

创建 /etc/ss-redir.json 本地监听 7777 运行ss-redir -v -c /etc/ss-redir.json

iptables -t nat -N SHADOWSOCKS
# 在 nat 表中创建新链
iptables -t nat -A SHADOWSOCKS -p tcp --dport 23596 -j RETURN
# 23596 是 ss 代理服务器的端口，即远程 shadowsocks 服务器提供服务的端口，如果你有多个 ip 可用,但端口一致，就设置这个

	Latency Comparison Numbers
	--------------------------
	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

	#!/bin/sh
	#
	set -ex

	TEMP_DIR="$(mktemp -d -t XXXX)"
	# cleanup
	trap 'RESULT=$?; rm -rf "$TEMP_DIR" ; exit $RESULT' INT TERM EXIT QUIT

	OLD_PWD="$PWD"
	cd "$TEMP_DIR"

	#!/bin/sh
	#
	set -ex

	TEMP_DIR="$(mktemp -d -t XXXX)"
	# cleanup
	trap 'RESULT=$?; rm -rf "$TEMP_DIR" ; exit $RESULT' INT TERM EXIT QUIT

	OLD_PWD="$PWD"
	cd "$TEMP_DIR"

	// http://help.adobe.com/en_US/FlashPlatform/reference/actionscript/3/package.html#encodeURIComponent()



	void hexchar(unsigned char c, unsigned char &hex1, unsigned char &hex2)
	{
	hex1 = c / 16;
	hex2 = c % 16;
	hex1 += hex1 <= 9 ? '0' : 'a' - 10;
	hex2 += hex2 <= 9 ? '0' : 'a' - 10;

	<?php

	if ( ! function_exists('array_group_by') ) :

	/**
	* Groups an array by a given key.
	*
	* Groups an array into arrays by a given key, or set of keys, shared between all array members.
	*
	* Based on {@author Jake Zatecky}'s {@link https://github.com/jakezatecky/array_group_by array_group_by()} function.

	# These steps will get nginx installed on your Mac for local development and
	# testing purposes, to be used alongside MAMP (which already includes Apache).
	# The following steps assume that you're running MAMP and that you already
	# have php-cgi in /Applications/MAMP/bin/php/php5.4.10/bin/php-cgi.
	# The start-nginx and stop-nginx scripts created at the end do not
	# start or stop MySQL because it is assumed that you normally run MAMP
	# with Apache + MySQL turned on and that you occasionally want to switch
	# your web server to Nginx for testing purposes and that you leave MySQL running.

	# This process was tested successfully on OS X 10.9.


	geo $limited {
	default 1;
	# Wordpress Jetpack ranges:
	192.0.0.0/16 0;
	66.135.0.0/16 0;
	66.155.0.0/16 0;
	76.74.0.0/16 0;
	}

	#!/bin/sh
	#
	# Originally part of vpnc source code:
	# © 2005-2012 Maurice Massar, Jörg Mayer, Antonio Borneo et al.
	# © 2009-2012 David Woodhouse <[email protected]>
	#
	# This program is free software; you can redistribute it and/or modify
	# it under the terms of the GNU General Public License as published by
	# the Free Software Foundation; either version 2 of the License, or
	# (at your option) any later version.