Joey Teng JoeyTeng

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

Trigonometry

const float PI = 3.1415926535897932384626433832795;
const float PI_2 = 1.57079632679489661923;
const float PI_4 = 0.785398163397448309616;

float PHI = (1.0+sqrtf(5.0))/2.0;

	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

	# Xcode 4.3.3
	Apple clang version 3.1 (tags/Apple/clang-318.0.61) (based on LLVM 3.1svn)
	Target: x86_64-apple-darwin11.4.0
	Thread model: posix

	# Xcode 4.3.2
	Apple clang version 3.1 (tags/Apple/clang-318.0.58) (based on LLVM 3.1svn)
	Target: x86_64-apple-darwin11.4.0
	Thread model: posix

	#!/bin/bash
	set -e

	# Usage:
	# rsync_parallel.sh [--parallel=N] [rsync args...]
	#
	# Options:
	# --parallel=N Use N parallel processes for transfer. Defaults to 10.
	#
	# Notes:

	#include <stdio.h>
	#include <stdlib.h>

	#define STACK_SIZE (1 << 26)
	#define STACK_PAD 128

	int rec(int n) {
	return n == 0 ? 0 : rec(n - 1) + 1;
	}

	# Example usage
	# $ python dft.py \| gnuplot
	# 9
	# 0 0
	# 1 1
	# 2 2
	# 0 2
	# 1 1
	# -1 1
	# 0 2

	// Just before switching jobs:
	// Add one of these.
	// Preferably into the same commit where you do a large merge.
	//
	// This started as a tweet with a joke of "C++ pro-tip: #define private public",
	// and then it quickly escalated into more and more evil suggestions.
	// I've tried to capture interesting suggestions here.
	//
	// Contributors: @r2d2rigo, @joeldevahl, @msinilo, @_Humus_,
	// @YuriyODonnell, @rygorous, @cmuratori, @mike_acton, @grumpygiant,

	Remuxing

	Why Remux Blu-rays?
	-You use MPC-HC (or similar DShow players) and standard filters for playback. You can also use better quality renderers like Haali, EVR and madVR.
	-You get the ease of playback of a re-encode without the quality loss. A double click off the .mkv will start the movie - no annoying warnings, loading screens, previews and setup menus.
	-You don't have to deal with horribly bloated, unstable and expensive PowerDVD or Arcsoft playback software.
	-You don't have to mess with ISO creation, correct BD folder structure, UDF and SPTD drivers, and image mounting every time you want to watch a movie.
	-You never have to worry about the region code setting of a disc.
	-You never have to worry about HDCP or PAP content protection.
	-You never have to worry about your software player downsampling your audio - get full bit-depth and frequency resolution, 24bit/96kHz or higher, not 16/48.

	#!/bin/zsh
	#
	# Copyright (c) 2014, 2020 by Dr. András Korn. Implements the basic idea of a similar script by Robert Coup (2013).
	# License: GPLv3

	function usage() {
	echo 'Usage:

	rsync_parallel [--parallel=N] <args to find(1) to generate list of stuff to transfer> -- <args to rsync>