[7152faa] | 1 | <?xml version="1.0" encoding="UTF-8"?>
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[b06ca36] | 2 | <!DOCTYPE sect1 PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
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| 3 | "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd" [
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[673b0d8] | 4 | <!ENTITY % general-entities SYSTEM "../general.ent">
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| 5 | %general-entities;
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| 6 | ]>
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[6a3b6af] | 7 |
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[afcfd74] | 8 | <sect1 id="ch-preps-aboutsbus">
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[6a3b6af] | 9 | <?dbhtml filename="aboutsbus.html"?>
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| 10 |
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| 11 | <title>About SBUs</title>
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| 12 |
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| 13 | <para>Many people would like to know beforehand approximately how long
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| 14 | it takes to compile and install each package. Because Linux From
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| 15 | Scratch can be built on many different systems, it is impossible to
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[7c92d6d] | 16 | provide absolute time estimates. The biggest package (gcc) will
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| 17 | take approximately 5 minutes on the fastest systems, but could take
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| 18 | days on slower systems! Instead of providing actual times,
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[6a3b6af] | 19 | the Standard Build Unit (SBU) measure will be
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| 20 | used instead.</para>
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| 21 |
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[7c92d6d] | 22 | <para>The SBU measure works as follows. The first package to be compiled is
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| 23 | binutils in <xref linkend="chapter-cross-tools"/>. The time it takes to
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[4990283] | 24 | compile using one core is what we will refer to as the Standard
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[7c92d6d] | 25 | Build Unit or SBU. All other compile times will be expressed in terms of this
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| 26 | unit of time.</para>
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[6a3b6af] | 27 |
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| 28 | <para>For example, consider a package whose compilation time is 4.5
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[ef93b66] | 29 | SBUs. This means that if your system took 10 minutes to compile and
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[ee714d3] | 30 | install the first pass of binutils, it will take
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[ef93b66] | 31 | <emphasis>approximately</emphasis> 45 minutes to build the example package.
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| 32 | Fortunately, most build times are shorter than one SBU.</para>
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[6a3b6af] | 33 |
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[ef93b66] | 34 | <para>SBUs are not entirely accurate because they depend on many
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[86861ee] | 35 | factors, including the host system's version of GCC. They are provided here
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| 36 | to give an estimate of how long it might take to install a package, but the
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| 37 | numbers can vary by as much as dozens of minutes in some cases.</para>
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[6a3b6af] | 38 |
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[3aee2ac2] | 39 | <note>
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| 40 | <para>When multiple processors are used in this way, the SBU units in the
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| 41 | book will vary even more than they normally would. In some cases, the make
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| 42 | step will simply fail. Analyzing the output of the build process will also
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[ef93b66] | 43 | be more difficult because the lines from different processes will be
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| 44 | interleaved. If you run into a problem with a build step, revert to a
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[3aee2ac2] | 45 | single processor build to properly analyze the error messages.</para>
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[7c92d6d] | 46 |
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| 47 | <para>The times presented here are based upon using four cores (-j4). The
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| 48 | times in Chapter 8 also include the time to run the regression tests for
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| 49 | the package unless specified otherwise.</para>
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| 50 |
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[86861ee] | 51 | </note>
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| 52 |
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[673b0d8] | 53 | </sect1>
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[81fd230] | 54 |
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