liaoyw liaoyw

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

tmux shortcuts & cheatsheet

start new:

tmux

start new with session name:

tmux new -s myname

	https://stackoverflow.com/a/11910583/5797497
	Old thread, but got exactly the same stupid mistake. /lib64 was moved to /lib64.bak remotely and everything stopped working.

	This was a x86_64 install, so ephemient's solution was not working:

	# /lib64.bak/ld-linux.so.2 --library-path /lib64.bak/ /bin/mv /lib64.bak/ /lib64
	/bin/mv: error while loading shared libraries: /bin/mv: wrong ELF class: ELFCLASS64
	In that case, a different ld-linux had to be used:

	# /lib64.bak/ld-linux-x86-64.so.2 --library-path /lib64.bak/ /bin/mv /lib64.bak/ /lib64

	# gdb -ex 'set print thread-events off' --batch -q -x ~/df.py
	import os
	import os.path
	import sys
	import gdb

	pid = open('/var/run/docker.pid', 'r').read()
	print 'attach to ' + pid
	gdb.execute('attach ' + pid)
	os.chdir('/proc/%s/fd'%pid)

	git_branch() {
	gb=$(git branch 2>/dev/null \| grep '^' \| tr -d ' ')
	[[ ! -z $gb ]] && echo "($gb)"
	}
	export PS1="\\W\$(git_branch) $"

	# open macdown from terminal
	# from https://github.com/MacDownApp/macdown/wiki/Advanced-Usage

	macdown() {
	"$(mdfind kMDItemCFBundleIdentifier=com.uranusjr.macdown \| head -n1)/Contents/SharedSupport/bin/macdown" $@
	}

	# encoding: utf-8

	import zlib

	"""
	copy from:
	https://github.com/afirel/consistent_hashr/blob/master/lib/consistent_hashr.rb
	http://www.tom-e-white.com/2007/11/consistent-hashing.html
	"""
	class ConsistentHash(object):

	# copy from http://www.tldp.org/LDP/abs/html/sample-bashrc.html
	function extract() # Handy Extract Program
	{
	if [ -f $1 ] ; then
	case $1 in
	*.tar.bz2) tar xvjf $1 ;;
	*.tar.gz) tar xvzf $1 ;;
	*.bz2) bunzip2 $1 ;;
	*.rar) unrar x $1 ;;
	*.gz) gunzip $1 ;;