1 | <?xml version="1.0" encoding="ISO-8859-1"?>
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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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4 | <!ENTITY % general-entities SYSTEM "../general.ent">
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5 | %general-entities;
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6 | ]>
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7 |
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8 | <sect1 id="ch-preps-aboutsbus">
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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-cross-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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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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38 |
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39 | <note>
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40 | <para>For many modern systems with multiple processors (or cores) the
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41 | compilation time for a package can be reduced by performing a "parallel
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42 | make" by either setting an environment variable or telling the
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43 | <command>make</command> program how many processors are available. For
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44 | instance, an Intel i5-6500 CPU can support four simultaneous processes with:</para>
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45 |
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46 | <screen role="nodump"><userinput>export MAKEFLAGS='-j4'</userinput></screen>
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47 |
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48 | <para>or just building with:</para>
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49 |
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50 | <screen role="nodump"><userinput>make -j4</userinput></screen>
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51 |
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52 | <para>When multiple processors are used in this way, the SBU units in the
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53 | book will vary even more than they normally would. In some cases, the make
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54 | step will simply fail. Analyzing the output of the build process will also
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55 | be more difficult because the lines of different processes will be
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56 | interleaved. If you run into a problem with a build step, revert back to a
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57 | single processor build to properly analyze the error messages.</para>
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58 | </note>
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59 |
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60 | </sect1>
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61 |
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