438c1335da
Also added support for the sysctl tunings taken from the environment and conditional tunings (i.e. not to change the sysctl settings if the current value is greater than the new value). To use the environment variable SEM: kernel.sem = $SEM To set the kernel.shmall only if the current value is less than the 1000000: kernel.shmall = >$1000000 Both can be combined, e.g.: kernel.shmall = >$SHMALL Signed-off-by: Jaroslav Škarvada <jskarvad@redhat.com>
147 lines
5.4 KiB
Text
147 lines
5.4 KiB
Text
ktune
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===============================================================================
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This description will give you a quick overview of ktune and what it can do for
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you.
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1) What is ktune?
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2) What it does
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2.1) ktune start
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2.2) ktune stop
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3) How you can use it
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4) How you can extend it
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5) Planned features
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1) What is ktune?
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-------------------------------------------------------------------------------
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The kernel in a Linux system is configured to fit the needs of a lot of
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customers and use cases. But for certain use cases these defaults might not be
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appropriate. For example there are use cases where much more shared memory
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segments are needed as with others. Also the size of network buffers might be
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important and also the elevator used for block devices to get maximum
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performance.
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Initially the service ktune was created to have a simple way to tune kernel
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parameters according to a usage profile. Over time this service has been
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expanded to support multiple profiles and provide more than kernel parameter
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tuning as well as adding a way for customers to use their own tuning settings.
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The package ktune provides a service init script together with a global config
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file and a sysctl throughput settings file, a directory to store additional
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profiles and some documentation.
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/etc/rc.d/init.d/ktune
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/etc/sysconfig/ktune
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/etc/sysctl.ktune
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/etc/ktune.d/
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/usr/share/doc/ktune-0.4
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/usr/share/doc/ktune-0.4/COPYING
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/usr/share/doc/ktune-0.4/README
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2) What it does
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-------------------------------------------------------------------------------
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ktune is a system service that is primarily managed by chkconfig. If the
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service is enabled and started, it will use the configuration options from
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/etc/sysconfig/ktune:
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SYSCTL="/etc/sysctl.ktune"
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USE_KTUNE_D="yes"
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SYSCTL_PRE="/etc/sysctl.d/* /etc/sysctl.conf"
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SYSCTL_POST="/etc/sysctl.d/* /etc/sysctl.conf"
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ELEVATOR="deadline"
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ELEVATOR_TUNE_DEVS="/sys/block/{sd,cciss}*/queue/scheduler"
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SYSCTL is the primary ktune sysctl profile. If you comment it out, it will not
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get applied.
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USE_KTUNE_D is a switch, that enables or disabled the use of additional
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profiles from the /etc/ktune.d directory. A profile has to have the extension
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.conf to be used. If there is an additional file with the same name, but the
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extension .sh it will be used as a profile script.
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SYSCTL_PRE references the system wide sysctl file for customer settings that
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is loaded before the ktune tunings. The tunings from this file may be
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overridden by ktune settings. Most profile don't use this option.
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SYSCTL_POST references the system wide sysctl file for customer settings that
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is loaded after the ktune tunings. This may override the ktune settings.
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ELEVATOR is the I/O scheduler, ktune will set for ELEVATOR_TUNE_DEVS. If you
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want to disable the setting of the I/O scheduler, just comment out the ELEVATOR
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line. ktune will not apply any scheduler if a scheduler is set on the kernel
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command line. It is safe to leave this on "deadline", but "as", "cfq", and
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"noop" are also legal values. ELEVATOR_TUNE_DEVS references the devices which
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should be tuned with the ELEVATOR.
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2.1) ktune start
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When the service starts, it is applying the sysctl settings from the SYSCTL
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file and afterwards the sysctl settings from the conf files in the /etc/ktune.d
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directory. For each sysctl settings, that will be modified, it will store the
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original value in a save file to be able to restore the initial settings if the
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service is stopped. This way it can easily be evaluated if settings are good or
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bad for a specific environment. After a profile from the ktune.d directory has
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been applied, the profile script will be called if available. The script will
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get the service parameter, the service has been started with: If "service ktune
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start" has been used, profile scripts will be called with the parameter
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"start". This way custom settings, for which the sysctl settings file can not
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be used, can be made.
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After applying the sysctl settings, the elevators will be set.
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2.2) ktune stop
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When the service stopps, it applies the settings saved while starting.
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3) How you can use it
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-------------------------------------------------------------------------------
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The service is managed by chkconfig and can be enabled or disabled for
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automatic system start and stop. If you want to evaluate settings or want to
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find te best settings for your system it is save to leave the service disabled
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and to start or stop it manually with the service command.
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To start or stop ktune you can use the service command:
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service ktune <start|stop>
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To enable or disable ktune for automatic system start, use the chkconfig
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command:
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chkconfig ktune <on|off>
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4) How you can extend it
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-------------------------------------------------------------------------------
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To change the primary profile, use the SYSCTL variable in the ktune sysconfig
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file. If you want to add additional profiles, put them into the /etc/ktune.d
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directory altogether with a profile scrip if needed.
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Skeleton of a profile scipt:
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#!/bin/sh
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case "$1" in
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start)
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# do something
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RETVAL=$?
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;;
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stop)
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# do something
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RETVAL=$?
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;;
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*)
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echo $"Usage: $0 {start|stop}"
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RETVAL=2
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;;
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esac
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exit $RETVAL
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5) Planned features
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-------------------------------------------------------------------------------
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* Readahead tuning for block devices
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