| 1 | <sect1 id="ch02-aboutsbus">
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| 2 | <title>About SBUs</title>
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| 3 | <?dbhtml filename="aboutsbus.html" dir="chapter02"?>
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| 4 |
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| 5 | <para>Most people would like to know beforehand how long it approximately
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| 6 | takes to compile and install each package. But "Linux from Scratch" is built
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| 7 | on so many different systems, it is not possible to give actual times that are
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| 8 | anywhere near accurate: the biggest package (Glibc) won't take more than
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| 9 | twenty minutes on the fastest systems, but will take something like three days
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| 10 | on the slowest -- no kidding. So instead of giving actual times, we've come up
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| 11 | with the idea of using the <emphasis>Static Binutils Unit</emphasis>
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| 12 | (abbreviated to <emphasis>SBU</emphasis>).</para>
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| 13 |
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| 14 | <para>It works like this: the first package you compile in this book is the
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| 15 | statically linked Binutils in <xref linkend="chapter05"/>, and the time it
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| 16 | takes to compile this package is what we call the "Static Binutils Unit" or
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| 17 | "SBU". All other compile times will be expressed relative to this time.</para>
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| 18 |
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| 19 | <para>For example, the time it takes to build the static version of GCC is
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| 20 | &gcc-time-tools-pass1;s. This means that if on your system it took 10 minutes
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| 21 | to compile and install the static Binutils, then you know it will take
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| 22 | approximately 45 minutes to build the static GCC. Fortunately, most build times
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| 23 | are much shorter than the one of Binutils.</para>
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| 24 |
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| 25 | <para>Note that if the system compiler on your host is GCC-2 based, the SBUs
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| 26 | listed may end up being somewhat understated. This is because the SBU is based
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| 27 | on the very first package, compiled with the old GCC, while the rest of the
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| 28 | system is compiled with the newer GCC-&gcc-version; which is known to be
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| 29 | approximately 30% slower.</para>
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| 30 |
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| 31 | <para>Also note that SBUs don't work well for SMP-based machines. But if you're
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| 32 | so lucky as to have multiple processors, chances are that your system is so fast
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| 33 | that you won't mind.</para>
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| 34 |
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| 35 | <para>If you wish to see actual timings for specific machines, have a look at
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| 36 | <ulink url="http://www.linuxfromscratch.org/~bdubbs/"/>.</para>
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| 37 |
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| 38 | </sect1>
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| 39 |
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