[673b0d8] | 1 | <?xml version="1.0" encoding="ISO-8859-1"?>
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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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[673b0d8] | 8 | <sect1 id="prepare-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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| 16 | provide accurate time estimates. The biggest package (Glibc) will
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| 17 | take approximately 20 minutes on the fastest systems, but could take
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| 18 | up to three days on slower systems! Instead of providing actual times,
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| 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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| 22 | <para>The SBU measure works as follows. The first package to be compiled
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| 23 | from this book is Binutils in <xref linkend="chapter-temporary-tools"/>. The
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| 24 | time it takes to compile this package is what will be referred to as the
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| 25 | Standard Build Unit or SBU. All other compile times will be expressed relative
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| 26 | to this time.</para>
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| 27 |
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| 28 | <para>For example, consider a package whose compilation time is 4.5
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| 29 | SBUs. This means that if a system took 10 minutes to compile and
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| 30 | install the first pass of Binutils, it will take
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| 31 | <emphasis>approximately</emphasis> 45 minutes to build this example package.
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| 32 | Fortunately, most build times are shorter than the one for Binutils.</para>
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| 33 |
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| 34 | <para>In general, 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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| 39 | <para>To view actual timings for a number of specific machines, we recommend
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[77e97ae] | 40 | The LinuxFromScratch SBU Home Page at <ulink url="&lfs-root;~sbu/"/>.</para>
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[81fd230] | 41 |
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[86861ee] | 42 | <note><para>For many modern systems with multiple processors (or cores) the
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| 43 | compilation time for a package can be reduced by performing a "parallel make"
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| 44 | by either setting an environment variable or telling the
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| 45 | <command>make</command> program how many processors are available. For
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| 46 | instance, a Core2Duo can support two simultaneous processes with:</para>
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| 47 |
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[cef11ea] | 48 | <screen><userinput>export MAKEFLAGS='-j 2'</userinput></screen>
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[86861ee] | 49 |
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| 50 | <para>or just building with:</para>
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| 51 |
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| 52 | <screen><userinput>make -j2</userinput></screen>
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| 53 |
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| 54 | <para>When multiple processors are used in this way, the SBU units in the
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| 55 | book will vary even more than they normally would. Analyzing the output of
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| 56 | the build process will also be more difficult because the lines of different
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| 57 | processes will be interleaved. If you run into a problem with a build step,
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| 58 | revert back to a single processor build to properly analyze the error
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| 59 | messages.</para>
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| 60 |
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| 61 | </note>
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| 62 |
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[673b0d8] | 63 | </sect1>
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[81fd230] | 64 |
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