documentation: BB_NUMBER_THREADS and PARALLEL_MAKE suggestions
Text that suggests setting the BB_NUMBER_THREADS and PARALLEL_MAKE variables to speed build time has been updated to suggest a setting of twice the number of host cores supported. The 2x number came to light through a discussion on the project mailing list initiated by Robert P. J. Day. Reported-by: Robert P. J. Day (From yocto-docs rev: 1846b41a595b7bd905ca828eaa04112d1533d7a1) Signed-off-by: Scott Rifenbark <scott.m.rifenbark@intel.com> Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
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@ -562,9 +562,10 @@
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You should also be sure any other variables in which you are interested are set.
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Some variables to consider are <filename>BB_NUMBER_THREADS</filename>
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and <filename>PARALLEL_MAKE</filename>, both of which can greatly reduce your build time
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if you are using a multi-threaded development system (e.g. values of
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<filename>8</filename> and <filename>j 6</filename>, respectively are optimal
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for a development machine that has four available cores).</para></listitem>
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if your development system supports multiple cores.
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For development systems that support multiple cores, a good rule of thumb is to set
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both the <filename>BB_NUMBER_THREADS</filename> and <filename>PARALLEL_MAKE</filename>
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variables to twice the number of cores your system supports.</para></listitem>
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<listitem><para>Update the <filename>bblayers.conf</filename> file so that it includes
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the path to your new BSP layer.
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In this example you need to include the pathname to <filename>meta-mymachine</filename>.
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@ -221,9 +221,9 @@
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If your host development system supports multi-core and multi-thread capabilities,
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you can uncomment these statements and set the variables to significantly shorten
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the full build time.
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As a guideline, set <filename>BB_NUMBER_THREADS</filename> to twice the number
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of cores your machine supports and set <filename>PARALLEL_MAKE</filename> to one and
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a half times the number of cores your machine supports.
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As a guideline, set both <filename>BB_NUMBER_THREADS</filename> and
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<filename>PARALLEL_MAKE</filename> to twice the number
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of cores your machine supports.
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</note>
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</para>
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<para>
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@ -390,9 +390,8 @@
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build time if your host supports multi-core and multi-thread capabilities:
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<filename>BB_NUMBER_THREADS</filename> and <filename>PARALLEL_MAKE</filename>.
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If the host system has multiple cores then you can optimize build time
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by setting <filename>BB_NUMBER_THREADS</filename> to twice the number of
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cores and setting <filename>PARALLEL_MAKE</filename> to one and a half times the
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number of cores.</para></listitem>
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by setting both these variables to twice the number of
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cores.</para></listitem>
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<listitem><para><emphasis>Identify Your <filename>meta-kernel-dev</filename>
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Layer:</emphasis> The <filename>BBLAYERS</filename> variable in the
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<filename>bblayers.conf</filename> file found in the
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@ -927,7 +927,7 @@
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This variable is usually in the form <filename>-j 4</filename>, where the number
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represents the maximum number of parallel threads make can run.
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If you development host supports multiple cores a good rule of thumb is to set
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this variable to one and a half times the number of cores on the host.</para>
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this variable to twice the number of cores on the host.</para>
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</glossdef>
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</glossentry>
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@ -410,11 +410,8 @@
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<ulink url='http://www.yoctoproject.org/docs/latest/poky-ref-manual/poky-ref-manual.html#var-PARALLEL_MAKE'><filename>PARALLEL_MAKE</filename></ulink> variables.
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By default, these variables are commented out.
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However, if you have a multi-core CPU you might want to uncomment
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the lines and set the variable
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<filename>BB_NUMBER_THREADS</filename> equal to twice the number of your
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the lines and set both variables equal to twice the number of your
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host's processor cores.
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Also, you could set the variable <filename>PARALLEL_MAKE</filename> equal to
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1.5 times the number of processor cores.
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Setting these variables can significantly shorten your build time.
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</para>
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