Yang Hong styxyang

新老用户都可能遇到陷阱。下面我们列出频繁出现的问题，以及如何解决。在 Freenode IRC #nginx 频道，我们经常看到这些问题。

[TOC]

关于本指南

最常见的是有人试图从其他指南拷贝配置片段。并非所有的指南是错误的，但绝大部分是有问题的。

Testing of Xen vPMU filter options.

Three tests are executed on a simple program (noploop, which runs NOP in a loop). The first two show Linux "perf stat" summaries, and the third tests specific counters: the IPC ones, an architectural one, and a few extras. Which of these will work depends on the filter mode.

I'll begin by showing off and on, the current modes, and then the new modes: ipc and arch.

vpmu=off (default)

root@lgud-bgregg:~> xl dmesg | grep vpmu

On naming and cache

There are only two hard things in Computer Science: cache invalidation and naming things.

-- Phil Karlton

On reusing code

There are two "rules of three" in [software] reuse:

a. It is three times as difficult to build reusable components as single use components, and
b. a reusable component should be tried out in three different applications before it will be sufficiently general to accept into a reuse library.

	#include <stdio.h>
	#include <string.h>
	#include <securec.h>

	#define HELLOWORLD "helloworld"
	#define HELLOWORLD1 "helloworld1"
	int main()
	{
	char name[sizeof(HELLOWORLD)] = HELLOWORLD;
	char name1[sizeof(HELLOWORLD1)] = HELLOWORLD1;

	package main

	import (
	"errors"
	"log"
	"runtime"
	"sync/atomic"
	"time"
	)

	/*
	* 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 3 of the License, or
	* (at your option) any later version.
	*/

	#include <arpa/inet.h>
	#include <linux/if_packet.h>
	#include <stdio.h>

	<!-- Get NumLock on keypad to work on osx for G80-3494, Realforce and so on -->
	<!-- By https://groups.google.com/d/msg/osx-karabiner/-2ns5XVXXdQ/kDGIKVSztjwJ -->
	<item>
	<name>Map NumLock to OSX NumLock function</name>
	<identifier>private.pc_numlock_to_mac_numlock</identifier>
	<autogen>__KeyToKey__ KeyCode::KEYPAD_CLEAR, KeyCode::VK_IOHIKEYBOARD_TOGGLE_NUMLOCK</autogen>
	</item>

	#!/usr/bin/expect -f

	set timeout 10; # set timeout to -1 to wait forever
	set hda "obj/kern/kernel.img"

	# spawn qemu -nographic -hda $hda -serial "file:jos.out" -monitor null -no-reboot
	spawn qemu -nographic -hda $hda -monitor null -no-reboot

	# interact
	expect {

	perl -e '@r = ("A".."Z", 0..9); foreach (1..shift) { print join "", @r[ map { rand @r } 1..16 ], "\n" }' -- 8

	# perl -e 'print join "", ("A".."Z")[ map { rand @("A".."Z") } 1..shift ], "\n"' -- 16

	# `sudo' is needed on Debian
	lsof -n -i4TCP:7777