Documentation Kernel Beat

From FedoraProject

(Difference between revisions)
Jump to: navigation, search
m (filesystem > file system)
Line 5: Line 5:
 
== Improved Performance and Reduced Power with relatime ==
 
== 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 filesystem performance and reduces power consumption.
+
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 filesystem 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.
+
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.  
 
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.  

Revision as of 13:59, 14 April 2009

Contents

Linux Kernel

This section covers changes and important information regarding the 2.6.29 based kernel in Fedora 11.

Improved Performance and Reduced Power with relatime

The 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 /tmp 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 /tmp directory). An improved version of relatime has been 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:

rpm -qpl kernel-<version>.src.rpm

Changelog

To retrieve a log of changes to the package, run the following command:

rpm -q --changelog kernel-<version>

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.

Preparing for Kernel Development

Fedora 11 does not include the kernel-source package provided by older versions since only the kernel-devel package is required now to build external modules.

Important.png
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

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.