Documentation Kernel Beat

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== Linux Kernel ==
 
== Linux Kernel ==
  
This section covers changes and important information regarding the 2.6.29 based kernel in Fedora 11.   
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This section covers changes and important information regarding the 2.x based kernel in Fedora .   
  
== Improved Performance and Reduced Power with relatime ==
 
 
The [http://lwn.net/Articles/244829/ relatime] option is now enabled by default in Fedora 11.  It improves file system performance and reduces power consumption.
 
 
The POSIX standard requires operating systems to keep track of the last time each file was accessed by an application or the user, and to store this timestamp as part of the file system data. This timestamp, called ''atime'', is used in finding out which files are never used (to clean up the <code>/tmp</code> directory for example) or if a file has been looked at after it was last changed.
 
 
A significant downside to atime is that every time a file is accessed, the kernel has to write a new timestamp to the disk, at least after a few seconds of activity. These disk writes keep the disk and the link to the disk busy, which costs both performance and power.
 
 
Because some programs use atime, disabling by default is not practical. The Linux kernel has a feature called ''relatime'', which is an effective compromise between having some of the information that atime provides, without having the disk time updated as regularly. It works by updating the atime field on disk only if the file hasn't been accessed since the last time it was accessed before (to provide the new email detection capability) or when the last access was more than 1 day ago (to help programs and users clean up unused files in the <code>/tmp</code> directory). An improved version of relatime has been [https://www.redhat.com/archives/fedora-devel-list/2009-March/msg01612.html merged upstream] by Fedora developers in the 2.6.30 kernel and backported to the Fedora 11 kernel.
 
 
=== Version ===
 
 
Fedora may include additional patches to the kernel for improvements, bug fixes, or additional features. For this reason, the Fedora kernel may not be line-for-line equivalent to the so-called ''vanilla kernel'' from the kernel.org web site:
 
 
http://www.kernel.org/
 
 
To obtain a list of these patches, download the source RPM package and run the following command against it:
 
 
<pre>rpm -qpl kernel-<version>.src.rpm</pre>
 
 
=== Changelog ===
 
 
To retrieve a log of changes to the package, run the following command:
 
 
<pre>rpm -q --changelog kernel-<version></pre>
 
 
If you need a user friendly version of the changelog, refer to http://wiki.kernelnewbies.org/LinuxChanges. A short and full diff of the kernel is available from http://kernel.org/git. The Fedora version kernel is based on the Linus tree.
 
 
Customizations made for the Fedora version are available from http://cvs.fedoraproject.org.
 
 
<!--
 
THIS IS ALL OLD MATERIAL. --PWF 2009-04-02
 
=== Kernel Flavors ===
 
 
Fedora 11 includes the following kernel builds:
 
 
 
* Native kernel, for use in most systems.  Configured sources are available in the <code>kernel-devel</code> package.
 
 
* The kernel-PAE, for use in 32-bit x86 systems with more than 4GB of RAM, or with CPUs that have a NX (No eXecute) feature.  This kernel supports both uniprocessor and multi-processor systems.  Configured sources are available in the <code>kernel-PAE-devel</code> package.
 
 
* Debugging kernel, for use in debugging some kernel issues. Configured sources are available in the <code>kernel-debug-devel</code> package.
 
 
You may install kernel headers for all four kernel flavors at the same time. The files are installed in the <code>/usr/src/kernels/<version>[-PAE|-xen|-kdump] -<arch>/</code> tree. Use the following command:
 
 
<pre>su -c 'yum install kernel{,-PAE,-xen,-kdump}-devel'</pre>
 
 
Select one or more of these flavors, separated by commas and no spaces, as appropriate.  Enter the root password when prompted.
 
 
{{Admon/note|x86 Kernel Includes Kdump|Both the x86_64 and the i686 kernels are relocatable, so they no longer require a separate kernel for kdump capability. PPC64 still requires a separate kdump kernel.}}
 
 
{{Admon/note|x86 Kernel Includes Paravirtualization|Both the x86_64 and the i686 kernels contain paravirt_ops support, so they no longer require a separate kernel for running under a Xen hypervisor.}}
 
 
{{Admon/note|Default Kernel Provides SMP|There is no separate SMP kernel available for Fedora on i386, x86_64, and ppc64.  Multiprocessor support is provided by the native kernel.}}
 
 
{{Admon/note|PowerPC Kernel Support|There is no support for Xen or kdump for the PowerPC architecture in Fedora. 32-bit PowerPC still has a separate SMP kernel.}}
 
 
-->
 
=== Preparing for Kernel Development ===
 
 
Fedora 11 does not include the <code>kernel-source</code> package provided by older versions since only the <code>kernel-devel</code> package is required now to build external modules.
 
 
 
{{Admon/important|Custom Kernel Building|For information on kernel development and working with custom kernels, refer to http://fedoraproject.org/wiki/Building_a_custom_kernel.}}
 
  
 
=== Reporting Bugs ===
 
=== Reporting Bugs ===
  
 
Refer to http://kernel.org/pub/linux/docs/lkml/reporting-bugs.html for information on reporting bugs in the Linux kernel.  You may also use http://bugzilla.redhat.com for reporting bugs that are specific to Fedora.
 
Refer to http://kernel.org/pub/linux/docs/lkml/reporting-bugs.html for information on reporting bugs in the Linux kernel.  You may also use http://bugzilla.redhat.com for reporting bugs that are specific to Fedora.

Revision as of 03:42, 14 September 2009

Linux Kernel

This section covers changes and important information regarding the 2.x based kernel in Fedora .


Reporting Bugs

Refer to http://kernel.org/pub/linux/docs/lkml/reporting-bugs.html for information on reporting bugs in the Linux kernel. You may also use http://bugzilla.redhat.com for reporting bugs that are specific to Fedora.