lfs-book-zh_CN/chapter04/aboutsbus.xml

<?xml version="1.0" encoding="ISO-8859-1"?>
<!DOCTYPE sect1 PUBLIC "-//OASIS//DTD DocBook XML V4.3//EN" "http://www.oasis-open.org/docbook/xml/4.3/docbookx.dtd" [
  <!ENTITY % general-entities SYSTEM "../general.ent">
  %general-entities;
]>
<sect1 id="prepare-aboutsbus">
<title>About SBUs</title>
<?dbhtml filename="aboutsbus.html"?>

<para>Most people would like to know beforehand approximately how long it
takes to compile and install each package. But <quote>Linux from Scratch</quote> is built
on so many different systems, it is not possible to give actual times that are
anywhere near accurate: the biggest package (Glibc) won't take more than
twenty minutes on the fastest systems, but will take something like three days
on the slowest -- no kidding. So instead of giving actual times, we've come up
with the idea of using the <emphasis>Static Binutils Unit</emphasis>
(abbreviated to <emphasis>SBU</emphasis>).</para>

<para>It works like this: the first package you compile in this book is the
statically linked Binutils in <xref linkend="chapter-temporary-tools"/>, and the time it
takes to compile this package is what we call the <quote>Static Binutils
Unit</quote> or <quote>SBU</quote>. All other compile times will be expressed
relative to this time.</para>

<para>For example, consider a particular package whose compilation time is 4.5
SBUs. This means that if on your system it took 10 minutes to compile and
install the static Binutils, then you know it will take
<emphasis>approximately</emphasis> 45 minutes to build this package.
Fortunately, most build times are much shorter than the one of Binutils.</para>

<para>Note that if the system compiler on your host is GCC-2 based, the SBUs
listed may end up being somewhat understated. This is because the SBU is based
on the very first package, compiled with the old GCC, while the rest of the
system is compiled with the newer GCC-&gcc-version; which is known to be
approximately 30% slower.</para>

<para>Also note that SBUs don't work well for SMP-based machines. But if you're
so lucky as to have multiple processors, chances are that your system is so fast
that you won't mind.</para>

<para>If you wish to see actual timings for specific machines, have a look at
<ulink url="&lfs-root;~bdubbs/"/>.</para>

</sect1>