poky/documentation/ref-manual/usingpoky.xml

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<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>



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<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>
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