source: chapter04/aboutsbus.xml@ c5be634

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Last change on this file since c5be634 was c5be634, checked in by Bruce Dubbs <bdubbs@…>, 8 years ago

Update several URLs in Chapter 3.
Fix typo in Chapter 5, libstdc++.
Removed obsolete reference to acinstall in automake section.
Removed obsolete reference to sbu home page in Chapter 4.
Update installed programs for gdbm.

git-svn-id: http://svn.linuxfromscratch.org/LFS/trunk/BOOK@10556 4aa44e1e-78dd-0310-a6d2-fbcd4c07a689

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1<?xml version="1.0" encoding="ISO-8859-1"?>
2<!DOCTYPE sect1 PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
3 "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd" [
4 <!ENTITY % general-entities SYSTEM "../general.ent">
5 %general-entities;
6]>
7
8<sect1 id="prepare-aboutsbus">
9 <?dbhtml filename="aboutsbus.html"?>
10
11 <title>About SBUs</title>
12
13 <para>Many people would like to know beforehand approximately how long
14 it takes to compile and install each package. Because Linux From
15 Scratch can be built on many different systems, it is impossible to
16 provide accurate time estimates. The biggest package (Glibc) will
17 take approximately 20 minutes on the fastest systems, but could take
18 up to three days on slower systems! Instead of providing actual times,
19 the Standard Build Unit (SBU) measure will be
20 used instead.</para>
21
22 <para>The SBU measure works as follows. The first package to be compiled
23 from this book is Binutils in <xref linkend="chapter-temporary-tools"/>. The
24 time it takes to compile this package is what will be referred to as the
25 Standard Build Unit or SBU. All other compile times will be expressed relative
26 to this time.</para>
27
28 <para>For example, consider a package whose compilation time is 4.5
29 SBUs. This means that if a system took 10 minutes to compile and
30 install the first pass of Binutils, it will take
31 <emphasis>approximately</emphasis> 45 minutes to build this example package.
32 Fortunately, most build times are shorter than the one for Binutils.</para>
33
34 <para>In general, SBUs are not entirely accurate because they depend on many
35 factors, including the host system's version of GCC. They are provided here
36 to give an estimate of how long it might take to install a package, but the
37 numbers can vary by as much as dozens of minutes in some cases.</para>
38
39 <note><para>For many modern systems with multiple processors (or cores) the
40 compilation time for a package can be reduced by performing a "parallel make"
41 by either setting an environment variable or telling the
42 <command>make</command> program how many processors are available. For
43 instance, a Core2Duo can support two simultaneous processes with:</para>
44
45 <screen><userinput>export MAKEFLAGS='-j 2'</userinput></screen>
46
47 <para>or just building with:</para>
48
49 <screen><userinput>make -j2</userinput></screen>
50
51 <para>When multiple processors are used in this way, the SBU units in the
52 book will vary even more than they normally would. Analyzing the output of
53 the build process will also be more difficult because the lines of different
54 processes will be interleaved. If you run into a problem with a build step,
55 revert back to a single processor build to properly analyze the error
56 messages.</para>
57
58 </note>
59
60</sect1>
61
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