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<!DOCTYPE chapter PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd"
[<!ENTITY % poky SYSTEM "../poky.ent"> %poky; ] >
<chapter id='usingpoky'>
<title>Using the Yocto Project</title>
<para>
This chapter describes common usage for the Yocto Project.
The information is introductory in nature as other manuals in the Yocto Project
documentation set provide more details on how to use the Yocto Project.
</para>
OLD START WAS HERE.
OLD END WAS HERE.
<section id='speeding-up-the-build'>
<title>Speeding Up the Build</title>
<para>
Build time can be an issue.
By default, the build system uses simple controls to try and maximize
build efficiency.
In general, the default settings for all the following variables
result in the most efficient build times when dealing with single
socket systems (i.e. a single CPU).
If you have multiple CPUs, you might try increasing the default
values to gain more speed.
See the descriptions in the glossary for each variable for more
information:
<itemizedlist>
<listitem><para>
<link linkend='var-BB_NUMBER_THREADS'><filename>BB_NUMBER_THREADS</filename>:</link>
The maximum number of threads BitBake simultaneously executes.
</para></listitem>
<listitem><para>
<ulink url='&YOCTO_DOCS_BB_URL;#var-BB_NUMBER_PARSE_THREADS'><filename>BB_NUMBER_PARSE_THREADS</filename>:</ulink>
The number of threads BitBake uses during parsing.
</para></listitem>
<listitem><para>
<link linkend='var-PARALLEL_MAKE'><filename>PARALLEL_MAKE</filename>:</link>
Extra options passed to the <filename>make</filename> command
during the
<link linkend='ref-tasks-compile'><filename>do_compile</filename></link>
task in order to specify parallel compilation on the
local build host.
</para></listitem>
<listitem><para>
<link linkend='var-PARALLEL_MAKEINST'><filename>PARALLEL_MAKEINST</filename>:</link>
Extra options passed to the <filename>make</filename> command
during the
<link linkend='ref-tasks-install'><filename>do_install</filename></link>
task in order to specify parallel installation on the
local build host.
</para></listitem>
</itemizedlist>
As mentioned, these variables all scale to the number of processor
cores available on the build system.
For single socket systems, this auto-scaling ensures that the build
system fundamentally takes advantage of potential parallel operations
during the build based on the build machine's capabilities.
</para>
<para>
Following are additional factors that can affect build speed:
<itemizedlist>
<listitem><para>
File system type:
The file system type that the build is being performed on can
also influence performance.
Using <filename>ext4</filename> is recommended as compared
to <filename>ext2</filename> and <filename>ext3</filename>
due to <filename>ext4</filename> improved features
such as extents.
</para></listitem>
<listitem><para>
Disabling the updating of access time using
<filename>noatime</filename>:
The <filename>noatime</filename> mount option prevents the
build system from updating file and directory access times.
</para></listitem>
<listitem><para>
Setting a longer commit:
Using the "commit=" mount option increases the interval
in seconds between disk cache writes.
Changing this interval from the five second default to
something longer increases the risk of data loss but decreases
the need to write to the disk, thus increasing the build
performance.
</para></listitem>
<listitem><para>
Choosing the packaging backend:
Of the available packaging backends, IPK is the fastest.
Additionally, selecting a singular packaging backend also
helps.
</para></listitem>
<listitem><para>
Using <filename>tmpfs</filename> for
<link linkend='var-TMPDIR'><filename>TMPDIR</filename></link>
as a temporary file system:
While this can help speed up the build, the benefits are
limited due to the compiler using
<filename>-pipe</filename>.
The build system goes to some lengths to avoid
<filename>sync()</filename> calls into the
file system on the principle that if there was a significant
failure, the
<link linkend='build-directory'>Build Directory</link>
contents could easily be rebuilt.
</para></listitem>
<listitem><para>
Inheriting the
<link linkend='ref-classes-rm-work'><filename>rm_work</filename></link>
class:
Inheriting this class has shown to speed up builds due to
significantly lower amounts of data stored in the data
cache as well as on disk.
Inheriting this class also makes cleanup of
<link linkend='var-TMPDIR'><filename>TMPDIR</filename></link>
faster, at the expense of being easily able to dive into the
source code.
File system maintainers have recommended that the fastest way
to clean up large numbers of files is to reformat partitions
rather than delete files due to the linear nature of partitions.
This, of course, assumes you structure the disk partitions and
file systems in a way that this is practical.
</para></listitem>
</itemizedlist>
Aside from the previous list, you should keep some trade offs in
mind that can help you speed up the build:
<itemizedlist>
<listitem><para>
Remove items from
<link linkend='var-DISTRO_FEATURES'><filename>DISTRO_FEATURES</filename></link>
that you might not need.
</para></listitem>
<listitem><para>
Exclude debug symbols and other debug information:
If you do not need these symbols and other debug information,
disabling the <filename>*-dbg</filename> package generation
can speed up the build.
You can disable this generation by setting the
<link linkend='var-INHIBIT_PACKAGE_DEBUG_SPLIT'><filename>INHIBIT_PACKAGE_DEBUG_SPLIT</filename></link>
variable to "1".
</para></listitem>
<listitem><para>
Disable static library generation for recipes derived from
<filename>autoconf</filename> or <filename>libtool</filename>:
Following is an example showing how to disable static
libraries and still provide an override to handle exceptions:
<literallayout class='monospaced'>
STATICLIBCONF = "--disable-static"
STATICLIBCONF_sqlite3-native = ""
EXTRA_OECONF += "${STATICLIBCONF}"
</literallayout>
<note><title>Notes</title>
<itemizedlist>
<listitem><para>
Some recipes need static libraries in order to work
correctly (e.g. <filename>pseudo-native</filename>
needs <filename>sqlite3-native</filename>).
Overrides, as in the previous example, account for
these kinds of exceptions.
</para></listitem>
<listitem><para>
Some packages have packaging code that assumes the
presence of the static libraries.
If so, you might need to exclude them as well.
</para></listitem>
</itemizedlist>
</note>
</para></listitem>
</itemizedlist>
</para>
</section>
</chapter>
<!--
vim: expandtab tw=80 ts=4
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