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documentation/dev-manual/dev-manual-kernel-appendix.xml: Kernel example fixed
Due to a bug (2256) the example that changes the kernel configuration through menuconfig did not work. I have re-written the section to now start with the default behavior of CONFIG_SMP=y and then have the user change the configuration to where it is not set. The changes include the reversing of the flow and the work-around needed due to bug 2256. (From yocto-docs rev: 6fa9eee12ed83f81470beb9792fb4fc1c5104f69) Signed-off-by: Scott Rifenbark <scott.m.rifenbark@intel.com> Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
This commit is contained in:
Scott Rifenbark
committed by
Richard Purdie
Richard Purdie
parent
0957740660
commit
3a062dde67
@@ -509,8 +509,8 @@
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<title>Changing the Kernel Configuration</title>
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<para>
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This example changes the default behavior, which is "off", of the Symmetric
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Multi-processing Support (<filename>CONFIG_SMP</filename>) to "on".
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This example changes the default behavior, which is "on", of the Symmetric
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Multi-processing Support (<filename>CONFIG_SMP</filename>) to "off".
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It is a simple example that demonstrates how to reconfigure the kernel.
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</para>
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@@ -533,7 +533,7 @@
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you can get them through tarball extraction or by
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cloning the <filename>poky</filename> Git repository.
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This example uses <filename>poky</filename> as the root directory of the
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local Yocto Project files Git repository.
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local <link linkend='yocto-project-files'>Yocto Project Files</link> Git repository.
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See the bulleted item
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"<link linkend='local-yp-release'>Yocto Project Release</link>"
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for information on how to get these files.
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@@ -616,11 +616,11 @@
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<title>Examining the Default <filename>CONFIG_SMP</filename> Behavior</title>
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<para>
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By default, <filename>CONFIG_SMP</filename> supports single processor machines.
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By default, <filename>CONFIG_SMP</filename> supports multiple processor machines.
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To see this default setting from within the QEMU emulator, boot your image using
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the emulator as follows:
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<literallayout class='monospaced'>
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$ runqemu qemux86 qemuparams="-smp 2"
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$ runqemu qemux86 qemuparams="-smp 4"
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</literallayout>
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</para>
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@@ -628,11 +628,25 @@
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Login to the machine using <filename>root</filename> with no password.
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After logging in, enter the following command to see how many processors are
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being supported in the emulator.
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The emulator reports support for a single processor:
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The emulator reports support for the number of processors you specified using
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the <filename>-smp</filename> option, four in this case:
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<literallayout class='monospaced'>
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# cat /proc/cpuinfo | grep processor
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processor : 0
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processor : 1
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processor : 2
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processor : 3
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#
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</literallayout>
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To check the setting for <filename>CONFIG_SMP</filename>, you can use the
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following command:
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<literallayout class='monospaced'>
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zcat /proc/config.gz | grep CONFIG_SMP
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</literallayout>
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The console returns the following showing that multi-processor machine support
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is set:
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<literallayout class='monospaced'>
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CONFIG_SMP=y
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</literallayout>
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Logout of the emulator using the <filename>exit</filename> command and
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then close it down.
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@@ -662,11 +676,21 @@
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kernel.
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The Yocto Project build environment recognizes this kernel as
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<filename>linux-yocto</filename>.
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Thus, the following command from the shell in which you previously sourced the
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environment initialization script launches <filename>menuconfig</filename>:
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Thus, the following commands from the shell in which you previously sourced the
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environment initialization script cleans the shared state memory and the
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<ulink url='&YOCTO_DOCS_REF_URL;#var-WORKDIR'><filename>WORKDIR</filename></ulink>
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directory and then builds and launches <filename>menuconfig</filename>:
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<literallayout class='monospaced'>
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$ bitbake linux-yocto -c cleansstate
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$ bitbake linux-yocto -c menuconfig
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</literallayout>
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<note>
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Due to a bug in the release, it is necessary to clean the shared state memory
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in order for configurations made using <filename>menuconfig</filename> to take
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effect.
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For information on the bug, see
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<ulink url='https://bugzilla.yoctoproject.org/show_bug.cgi?id=2256'></ulink>
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</note>
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</para>
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<para>
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@@ -675,7 +699,7 @@
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You can find it at <filename>Processor Type and Features</filename>.
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The configuration selection is
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<filename>Symmetric Multi-processing Support</filename>.
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After using the arrow keys to highlight this selection, press "y" to select it.
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After using the arrow keys to highlight this selection, press "n" to turn it off.
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Then, exit out and save your selections.
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</para>
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@@ -684,22 +708,25 @@
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is updated.
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This is the file that the build system uses to configure the Linux Yocto kernel
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when it is built.
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You can find and examine this file in the Yocto Project files Git repository in
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You can find and examine this file in the Yocto Project Files Git repository in
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the build directory.
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This example uses the following.
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Note that this example directory is artificially split and many of the characters
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in the actually filename are omitted in order to make it more
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readable:
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This example uses the following:
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<literallayout class='monospaced'>
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~/poky/build/tmp/work/qemux86-poky-linux/linux-yocto-2.6.37+git1+84f...
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...r20/linux-qemux86-standard-build
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~/poky/build/tmp/work/qemux86-poky-linux/linux-yocto-3.2.11+git1+84f...
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...656ed30-r1/linux-qemux86-standard-build
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</literallayout>
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<note>
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The previous example directory is artificially split and many of the characters
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in the actual filename are omitted in order to make it more readable.
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Also, depending on the kernel you are using, the exact pathname might differ
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slightly.
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</note>
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</para>
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<para>
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Within the <filename>.config</filename> file, you can see the following setting:
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<literallayout class='monospaced'>
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CONFIG_SMP=y
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# CONFIG_SMP is not set
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</literallayout>
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</para>
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@@ -735,9 +762,9 @@
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</para>
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<para>
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Now run the QEMU emulator:
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Now run the QEMU emulator and pass it the same multi-processor option as before:
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<literallayout class='monospaced'>
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$ runqemu qemux86 qemuparams="-smp 2"
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$ runqemu qemux86 qemuparams="-smp 4"
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</literallayout>
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</para>
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@@ -747,13 +774,22 @@
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<literallayout class='monospaced'>
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# cat /proc/cpuinfo | grep processor
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processor : 0
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processor : 1
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#
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</literallayout>
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</para>
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<para>
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From the output, you can see that you have successfully reconfigured the kernel.
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From the output, you can see that the kernel no longer supports multi-processor systems.
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The output indicates support for a single processor. You can verify the
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<filename>CONFIG_SMP</filename> setting by using this command:
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<literallayout class='monospaced'>
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zcat /proc/config.gz | grep CONFIG_SMP
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</literallayout>
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The console returns the following output:
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<literallayout class='monospaced'>
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# CONFIG_SMP is not set
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</literallayout>
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You have successfully reconfigured the kernel.
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</para>
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</section>
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</section>
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