Difference between revisions of "Readahead-fedora"

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[[Category:Boot process]]
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#REDIRECT [[Improving performance/Boot process]]
Readahead-fedora is originally developed by Fedora, and contrary to [[ureadahead]], it does not require patching the kernel. It creates a list of files to put in the page cache before they are needed, thus reducing boot time.
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== Advantages ==
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* It does not require patching the kernel.
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* It can take multiple lists of files to be preloaded, and sort them according to their position on the disk.
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* It preloads the inode tables on ext2-based file systems.
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* It opens the files without making the system update their access time, therefore avoiding extra disk writes. <sub>''(Though, this shouldn't matter when using relatime or noatime I think)''</sub>
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* It uses a lightweight monitoring daemon.
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<sub>''(List shamelessly stolen from the debian package description, [http://packages.debian.org/unstable/readahead-fedora original here])''</sub>
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== Installation ==
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Ying has created a [[PKGBUILD]] for this project; it is named {{AUR|readahead-fedora}} in the [[Arch User Repository|AUR]].
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{{Note|libprelude currently doesn't build with libtool-2.4. Either downgrade to 2.2.10-3 or wait for a workaround.}}
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== Configuration ==
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All configuration is done through {{ic|/etc/readahead.conf}}. Some interesting variables might be:
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TIMEOUT_SWITCH_TO_LATER="8"
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This determines the timeout for the collector while X and such is starting.
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RAC_MAXTIME="100"
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A value in seconds that determine how long the collector should run.
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RAC_INITPATH="/sbin/init"
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A path to your init program. Change this if you use anything other than sysvinit.
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RAC_EXECIGN="/sbin/readahead /usr/sbin/preload"
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If you want the collector to ignore syscalls from certain programs, this is where you set their paths.
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RAC_EXCLUDE="/proc /sys /dev /var/log /var/run /var/lock /home /tmp /var/tmp /media /selinux /mnt"
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Directories to ignore while collecting. Anything that is not needed during boot should probably be here to keep the list slimmed down.
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== Usage ==
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The package installs the file {{ic|/etc/rc.d/functions.d/readahead}}. This file will automatically start readahead at the appropriate times, control the collector and all that.
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If you have dbus installed, readahead will automatically start it before X starts to avoid any issues.
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The file {{ic|/.readahead}} should automatically be created when installing the package. This is to let readahead-collector profile your system next boot.
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=== Automated profiling ===
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This is actually really easy, just add a cron job that creates the file {{ic|/.readahead}} every month or so.
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=== Manually reprofile the system ===
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There are two ways to do this, either just run
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$ touch /.readahead
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as root, or you can '''temporarily''' add
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init=/sbin/readahead-collector
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to the kernel line in your bootloader. You should also disable auditd, because auditd deletes all audit rules during boot, which is contraproductive for the collector. Now, you just need to reboot and let the collector profile your system.
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== Trimming down boot-times ==
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The package edits your inittab to take advantage of the early - later split in readahead-fedora. What it basically does is move these lines around:
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...
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rc::sysinit:/etc/rc.sysinit
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rs:S1:wait:/etc/rc.single
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'''#rm:2345:wait:/etc/rc.multi'''
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'''#rh:06:wait:/etc/rc.shutdown'''
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'''#su:S:wait:/sbin/sulogin -p'''
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...
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# Example lines for starting a login manager
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#x:5:respawn:/usr/bin/xdm -nodaemon
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#x:5:respawn:/usr/sbin/gdm -nodaemon
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#x:5:respawn:/usr/bin/kdm -nodaemon
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#x:5:respawn:/usr/bin/slim >& /dev/null
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'''rm:2345:wait:/etc/rc.multi > /dev/null'''
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'''rh:06:wait:/etc/rc.shutdown'''
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'''su:S:wait:/sbin/sulogin -p'''
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# End of file
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{{Note|The old inittab is backed up as {{ic|/etc/inittab.backup}}.}}
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The idea of doing it this way is that readahead will put the needed X-stuff in the early cache. Thus, while X is starting it will have time to read the later cache for starting the daemons.
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{{Note|Since we cannot have multi starting early, we cannot use :once: instead of :wait: to make boot asynchronous.}}
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== Notes ==
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You might wonder what this file does while profiling:
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...
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readahead-later() {
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  if [ -e /.readahead ]; then
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      sleep 8
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      touch '''/.switch-collector-to-later'''
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      rm /.readahead
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  else
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...
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Readahead-fedora uses two steps to read and create the cache, called "early" and "later". Why it does it this way is to have a small, neat cache that it initially reads. This basically contains the basic files needed to boot together with X. After it has read those files and started X, it reads the "later" cache for starting the various daemons and services. This way, it tries to be a bit smarter and dynamic in hiding load times.
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== Links ==
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*[https://fedorahosted.org/readahead/browser/README README] from fedorahosted.org
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*[http://packages.debian.org/unstable/readahead-fedora Package info] from the Debian package tree.
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*{{AUR|quick-boot}} in the AUR.
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*[https://wiki.archlinux.de/title/Readahead-fedora Article by ying] in German.
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Latest revision as of 04:17, 27 August 2016