mirror of https://github.com/tLDP/LDP
62 lines
2.8 KiB
XML
62 lines
2.8 KiB
XML
<?xml version="1.0" encoding="ISO-8859-1"?>
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<!DOCTYPE sect1 PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
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"http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd" [
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<!ENTITY % general-entities SYSTEM "../general.ent">
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%general-entities;
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]>
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<sect1 id="prepare-aboutsbus">
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<?dbhtml filename="aboutsbus.html"?>
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<title>About SBUs</title>
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<para>Many people would like to know beforehand approximately how long
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it takes to compile and install each package. Because Linux From
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Scratch can be built on many different systems, it is impossible to
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provide accurate time estimates. The biggest package (Glibc) will
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take approximately 20 minutes on the fastest systems, but could take
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up to three days on slower systems! Instead of providing actual times,
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the Standard Build Unit (SBU) measure will be
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used instead.</para>
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<para>The SBU measure works as follows. The first package to be compiled
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from this book is Binutils in <xref linkend="chapter-temporary-tools"/>. The
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time it takes to compile this package is what will be referred to as the
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Standard Build Unit or SBU. All other compile times will be expressed relative
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to this time.</para>
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<para>For example, consider a package whose compilation time is 4.5
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SBUs. This means that if a system took 10 minutes to compile and
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install the first pass of Binutils, it will take
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<emphasis>approximately</emphasis> 45 minutes to build this example package.
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Fortunately, most build times are shorter than the one for Binutils.</para>
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<para>In general, SBUs are not entirely accurate because they depend on many
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factors, including the host system's version of GCC. They are provided here
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to give an estimate of how long it might take to install a package, but the
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numbers can vary by as much as dozens of minutes in some cases.</para>
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<note>
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<para>For many modern systems with multiple processors (or cores) the
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compilation time for a package can be reduced by performing a "parallel
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make" by either setting an environment variable or telling the
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<command>make</command> program how many processors are available. For
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instance, a Core2Duo can support two simultaneous processes with:</para>
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<screen><userinput>export MAKEFLAGS='-j 2'</userinput></screen>
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<para>or just building with:</para>
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<screen><userinput>make -j2</userinput></screen>
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<para>When multiple processors are used in this way, the SBU units in the
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book will vary even more than they normally would. In some cases, the make
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step will simply fail. Analyzing the output of the build process will also
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be more difficult because the lines of different processes will be
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interleaved. If you run into a problem with a build step, revert back to a
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single processor build to properly analyze the error messages.</para>
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</note>
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</sect1>
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