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aboutsbus: Add power profile info

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Xi Ruoyao 2024-08-26 02:49:01 +08:00
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chapter04/aboutsbus.xml
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@ -36,6 +36,32 @@
to give an estimate of how long it might take to install a package, but the
numbers can vary by as much as dozens of minutes in some cases.</para>
<para>Before measuring the build time of any package (no matter Binutils
pass 1 or a package of which the SBU is being measured), make sure a
system power profile suitable to make the system running with the
maximum performance (and the maximum power consumption) is selected. Or
the measured SBU value may be severly inaccurate because the system may be
operated differently building Binutils pass 1 and the other package.
Be aware that a significant inaccuracy can still show up even if the same
profile (except one maximizing the performance) is used for both packages:
the system may respond slower for <quote>saving the power</quote> building
Binutils pass 1, because the system load seems only about 25% of the load
building the other package (with <parameter>-j4</parameter>).</para>
<para>On most distros the power profile can be managed with either
<command>power-profiles-daemon</command> or <command>tuned</command>.
If the distro runs <command>power-profiles-daemon</command>, issue the
<command>powerprofilesctl set performance</command> command to select
the <literal>performance</literal> profile. If the distro runs
<command>tuned</command>, issue the <command>tuned-adm profile
throughput-performance</command> command to select the
<literal>throughput-performance</literal> profile.</para>
<para>Even if you are not measuring the SBU values, it's still better to
select the power profile for maximum performance before building LFS, as
doing so can (obviously) make the system faster to build LFS
packages.</para>
<note>
<para>When multiple processors are used in this way, the SBU units in the
book will vary even more than they normally would. In some cases, the make
@ -47,7 +73,6 @@
<para>The times presented here are based upon using four cores (-j4). The
times in Chapter 8 also include the time to run the regression tests for
the package unless specified otherwise.</para>
</note>
</sect1>