| 1 | <?xml version="1.0" encoding="ISO-8859-1"?>
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| 2 | <!DOCTYPE sect1 PUBLIC "-//OASIS//DTD DocBook XML V4.4//EN" "http://www.oasis-open.org/docbook/xml/4.4/docbookx.dtd" [
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| 3 | <!ENTITY % general-entities SYSTEM "../general.ent">
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| 4 | %general-entities;
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| 5 | ]>
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| 6 | <sect1 id="prepare-aboutsbus">
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| 7 | <title>About SBUs</title>
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| 8 | <?dbhtml filename="aboutsbus.html"?>
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| 9 |
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| 10 | <para>Many people would like to know beforehand approximately how long
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| 11 | it takes to compile and install each package. Because Linux From
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| 12 | Scratch can be built on many different systems, it is impossible to
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| 13 | provide accurate time estimates. The biggest package (Glibc) will
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| 14 | take approximately 20 minutes on the fastest systems, but could take
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| 15 | up to three days on slower systems! Instead of providing actual times,
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| 16 | the Standard Build Unit (SBU) measure will be
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| 17 | used instead.</para>
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| 18 |
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| 19 | <para>The SBU measure works as follows. The first package to be compiled
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| 20 | from this book is Binutils in <xref linkend="chapter-temporary-tools"/>. The
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| 21 | time it takes to compile this package is what will be referred to as the
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| 22 | Standard Build Unit or SBU. All other compile times will be expressed relative
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| 23 | to this time.</para>
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| 24 |
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| 25 | <para>For example, consider a package whose compilation time is 4.5
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| 26 | SBUs. This means that if a system took 10 minutes to compile and
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| 27 | install the first pass of Binutils, it will take
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| 28 | <emphasis>approximately</emphasis> 45 minutes to build this example package.
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| 29 | Fortunately, most build times are shorter than the one for Binutils.</para>
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| 30 |
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| 31 | <para>In general, SBUs are not entirely accurate because they depend on many
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| 32 | factors, including the host system's version of GCC. Note that on Symmetric
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| 33 | Multi-Processor (SMP)-based machines, SBUs are even less accurate. They are
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| 34 | provided here to give an estimate of how long it might take to install a
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| 35 | package, but the numbers can vary by as much as dozens of minutes in some
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| 36 | cases.</para>
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| 37 |
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| 38 | <para>To view actual timings for a number of specific machines, we recommend
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| 39 | The LinuxFromScratch SBU Home Page at <ulink url="&lfs-root;~bdubbs/"/>.</para>
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| 40 |
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| 41 | </sect1>
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| 42 |
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