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 Static 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 the statically-linked Binutils in <xref
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21 | linkend="chapter-temporary-tools"/>. The time it takes to compile
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22 | this package is what will be referred to as the Static Build Unit
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23 | or SBU. All other compile times will be expressed relative to this
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24 | time.</para>
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25 |
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26 | <para>For example, consider a package whose compilation time is 4.5
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27 | SBUs. This means that if a system took 10 minutes to compile and
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28 | install the static Binutils, it will take
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29 | <emphasis>approximately</emphasis> 45 minutes to build this example
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30 | package. Fortunately, most build times are shorter than the one
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31 | for Binutils.</para>
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32 |
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33 | <para>Please note that if the system compiler on the host is GCC-2.x based, the
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34 | SBUs listed may be somewhat understated. This is because the SBU is
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35 | based on the very first package, compiled with the old GCC, while the
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36 | rest of the system is compiled with the newer GCC-&gcc-version; (which is
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37 | known to be approximately 30 percent slower). SBUs are also not
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38 | highly accurate for Symmetric Multi-Processor (SMP)-based machines.</para>
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39 |
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40 | <para>To view actual timings for a number of specific machines, we recommend
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41 | <ulink url="&lfs-root;~bdubbs/"/>.</para>
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42 |
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43 | <para>In general, SBUs are not very accurate because they depend on many
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44 | factors, not just the GCC version. They are provided
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45 | here to give an estimate of how long it might take to
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46 | install a package, but the numbers can vary by as much as dozens of
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47 | minutes in some cases.</para>
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48 |
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49 | </sect1>
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50 |
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