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documentation/dev-manual/dev-manual-kernel-appendix.xml: Kernel example fixed

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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
2012-05-04 17:17:28 -06:00
committed by Richard Purdie
parent 0957740660
commit 3a062dde67
1 changed files with 57 additions and 21 deletions
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documentation/dev-manual/dev-manual-kernel-appendix.xml
+57 -21
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@@ -509,8 +509,8 @@
<title>Changing the Kernel Configuration</title> <title>Changing the Kernel Configuration</title>
<para> <para>
This example changes the default behavior, which is "off", of the Symmetric This example changes the default behavior, which is "on", of the Symmetric
Multi-processing Support (<filename>CONFIG_SMP</filename>) to "on". Multi-processing Support (<filename>CONFIG_SMP</filename>) to "off".
It is a simple example that demonstrates how to reconfigure the kernel. It is a simple example that demonstrates how to reconfigure the kernel.
</para> </para>
@@ -533,7 +533,7 @@
you can get them through tarball extraction or by you can get them through tarball extraction or by
cloning the <filename>poky</filename> Git repository. cloning the <filename>poky</filename> Git repository.
This example uses <filename>poky</filename> as the root directory of the This example uses <filename>poky</filename> as the root directory of the
local Yocto Project files Git repository. local <link linkend='yocto-project-files'>Yocto Project Files</link> Git repository.
See the bulleted item See the bulleted item
"<link linkend='local-yp-release'>Yocto Project Release</link>" "<link linkend='local-yp-release'>Yocto Project Release</link>"
for information on how to get these files. for information on how to get these files.
@@ -616,11 +616,11 @@
<title>Examining the Default&nbsp;&nbsp;<filename>CONFIG_SMP</filename> Behavior</title> <title>Examining the Default&nbsp;&nbsp;<filename>CONFIG_SMP</filename> Behavior</title>
<para> <para>
By default, <filename>CONFIG_SMP</filename> supports single processor machines. By default, <filename>CONFIG_SMP</filename> supports multiple processor machines.
To see this default setting from within the QEMU emulator, boot your image using To see this default setting from within the QEMU emulator, boot your image using
the emulator as follows: the emulator as follows:
<literallayout class='monospaced'> <literallayout class='monospaced'>
$ runqemu qemux86 qemuparams="-smp 2" $ runqemu qemux86 qemuparams="-smp 4"
</literallayout> </literallayout>
</para> </para>
@@ -628,11 +628,25 @@
Login to the machine using <filename>root</filename> with no password. Login to the machine using <filename>root</filename> with no password.
After logging in, enter the following command to see how many processors are After logging in, enter the following command to see how many processors are
being supported in the emulator. being supported in the emulator.
The emulator reports support for a single processor: The emulator reports support for the number of processors you specified using
the <filename>-smp</filename> option, four in this case:
<literallayout class='monospaced'> <literallayout class='monospaced'>
# cat /proc/cpuinfo | grep processor # cat /proc/cpuinfo | grep processor
processor : 0 processor : 0
processor : 1
processor : 2
processor : 3
# #
</literallayout>
To check the setting for <filename>CONFIG_SMP</filename>, you can use the
following command:
<literallayout class='monospaced'>
zcat /proc/config.gz | grep CONFIG_SMP
</literallayout>
The console returns the following showing that multi-processor machine support
is set:
<literallayout class='monospaced'>
CONFIG_SMP=y
</literallayout> </literallayout>
Logout of the emulator using the <filename>exit</filename> command and Logout of the emulator using the <filename>exit</filename> command and
then close it down. then close it down.
@@ -662,11 +676,21 @@
kernel. kernel.
The Yocto Project build environment recognizes this kernel as The Yocto Project build environment recognizes this kernel as
<filename>linux-yocto</filename>. <filename>linux-yocto</filename>.
Thus, the following command from the shell in which you previously sourced the Thus, the following commands from the shell in which you previously sourced the
environment initialization script launches <filename>menuconfig</filename>: environment initialization script cleans the shared state memory and the
<ulink url='&YOCTO_DOCS_REF_URL;#var-WORKDIR'><filename>WORKDIR</filename></ulink>
directory and then builds and launches <filename>menuconfig</filename>:
<literallayout class='monospaced'> <literallayout class='monospaced'>
$ bitbake linux-yocto -c cleansstate
$ bitbake linux-yocto -c menuconfig $ bitbake linux-yocto -c menuconfig
</literallayout> </literallayout>
<note>
Due to a bug in the release, it is necessary to clean the shared state memory
in order for configurations made using <filename>menuconfig</filename> to take
effect.
For information on the bug, see
<ulink url='https://bugzilla.yoctoproject.org/show_bug.cgi?id=2256'></ulink>
</note>
</para> </para>
<para> <para>
@@ -675,7 +699,7 @@
You can find it at <filename>Processor Type and Features</filename>. You can find it at <filename>Processor Type and Features</filename>.
The configuration selection is The configuration selection is
<filename>Symmetric Multi-processing Support</filename>. <filename>Symmetric Multi-processing Support</filename>.
After using the arrow keys to highlight this selection, press "y" to select it. After using the arrow keys to highlight this selection, press "n" to turn it off.
Then, exit out and save your selections. Then, exit out and save your selections.
</para> </para>
@@ -684,22 +708,25 @@
is updated. is updated.
This is the file that the build system uses to configure the Linux Yocto kernel This is the file that the build system uses to configure the Linux Yocto kernel
when it is built. when it is built.
You can find and examine this file in the Yocto Project files Git repository in You can find and examine this file in the Yocto Project Files Git repository in
the build directory. the build directory.
This example uses the following. This example uses the following:
Note that this example directory is artificially split and many of the characters
in the actually filename are omitted in order to make it more
readable:
<literallayout class='monospaced'> <literallayout class='monospaced'>
~/poky/build/tmp/work/qemux86-poky-linux/linux-yocto-2.6.37+git1+84f... ~/poky/build/tmp/work/qemux86-poky-linux/linux-yocto-3.2.11+git1+84f...
...r20/linux-qemux86-standard-build ...656ed30-r1/linux-qemux86-standard-build
</literallayout> </literallayout>
<note>
The previous example directory is artificially split and many of the characters
in the actual filename are omitted in order to make it more readable.
Also, depending on the kernel you are using, the exact pathname might differ
slightly.
</note>
</para> </para>
<para> <para>
Within the <filename>.config</filename> file, you can see the following setting: Within the <filename>.config</filename> file, you can see the following setting:
<literallayout class='monospaced'> <literallayout class='monospaced'>
CONFIG_SMP=y # CONFIG_SMP is not set
</literallayout> </literallayout>
</para> </para>
@@ -735,9 +762,9 @@
</para> </para>
<para> <para>
Now run the QEMU emulator: Now run the QEMU emulator and pass it the same multi-processor option as before:
<literallayout class='monospaced'> <literallayout class='monospaced'>
$ runqemu qemux86 qemuparams="-smp 2" $ runqemu qemux86 qemuparams="-smp 4"
</literallayout> </literallayout>
</para> </para>
@@ -747,13 +774,22 @@
<literallayout class='monospaced'> <literallayout class='monospaced'>
# cat /proc/cpuinfo | grep processor # cat /proc/cpuinfo | grep processor
processor : 0 processor : 0
processor : 1
# #
</literallayout> </literallayout>
</para> </para>
<para> <para>
From the output, you can see that you have successfully reconfigured the kernel. From the output, you can see that the kernel no longer supports multi-processor systems.
The output indicates support for a single processor. You can verify the
<filename>CONFIG_SMP</filename> setting by using this command:
<literallayout class='monospaced'>
zcat /proc/config.gz | grep CONFIG_SMP
</literallayout>
The console returns the following output:
<literallayout class='monospaced'>
# CONFIG_SMP is not set
</literallayout>
You have successfully reconfigured the kernel.
</para> </para>
</section> </section>
</section> </section>