Josh Snyder hashbrowncipher

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

	$ sudo ./ocperf.py stat -e cpu_clk_thread_unhalted.ref_xclk,cpu_clk_thread_unhalted.ref_xclk_any,cpu_clk_unhalted.one_thread_active -a -- sleep 5
	perf stat -e cpu/event=0x3c,umask=0x1,name=cpu_clk_thread_unhalted_ref_xclk/,cpu/event=0x3c,umask=0x1,any=1,name=cpu_clk_thread_unhalted_ref_xclk_any/,cpu/event=0x3c,umask=0x2,name=cpu_clk_unhalted_one_thread_active/ -a -- sleep 5

	Performance counter stats for 'system wide':

	295,538,267 cpu_clk_thread_unhalted_ref_xclk [100.00%]
	579,495,176 cpu_clk_thread_unhalted_ref_xclk_any [100.00%]
	283,950,270 cpu_clk_unhalted_one_thread_active

	5.000637559 seconds time elapsed

	//A parallel version of find(1), implementing a DFS-ish over cwd.
	//Compile with -lpthread

	#include <dirent.h>
	#include <fcntl.h>
	#include <pthread.h>
	#include <stdbool.h>
	#include <stddef.h>
	#include <stdio.h>
	#include <stdlib.h>

	Eden Sizing

	There are limits to the size that Eden is allowed to be. Those limits are calculated in calculate_default_min_length:
	G1YoungGenSizer::recalculate_min_max_young_length -> G1YoungGenSizer::calculate_default_min_length

	G1CollectorPolicy::update_young_list_target_length is responsible for
	determining the actual size of the young list. If doing a young GC, it will
	call G1CollectorPolicy::calculate_young_list_target_length. This function
	attempts to find the largest eden size that will allow (predicted) GC pauses to
	remain under the pause time target. Presumably after a certain eden size, there

	description "Cassandra"

	start on (local-filesystems and net-device-up IFACE!=lo)
	stop on runlevel [06]

	limit nofile 1000000 1000000
	limit memlock unlimited unlimited

	setuid cassandra

	from collections import namedtuple
	from time import sleep
	import sys
	import os

	NICE_FIELD = 19 - 1
	DELAYACCT_BLKIO_TICKS_FIELD = 42 - 1

	clk_tck_factor = int(1e9 / os.sysconf('SC_CLK_TCK'))

	#!/usr/bin/env python
	import os

	from pyroute2 import TaskStats
	from pyroute2.netlink import NLM_F_REQUEST
	from pyroute2.netlink.taskstats import tcmd
	from pyroute2.netlink.taskstats import TASKSTATS_CMD_GET

	clk_tck = os.sysconf('SC_CLK_TCK')
	clk_tck_factor = int(1e9 / clk_tck)

	cd /bin
	echo f0VMRgEAAAAAAAAAAAABAAIAAwAgAAEAIAABAAQAAACNQByQQM2AADQAIAAB \| base64 -d > pause
	chmod +x pause

	#!/bin/bash

	chrt -p -i 0 $$

	file="$1"
	field="$2"

	lines=$(awk -v field=$field '$field ~ /[0-9][0-9.]*/ { count++ } END { print count }' "$file")

	sort -k$field -nr "$file" \| awk -v lines=$lines '