Often, a detailed audit and analysis of a system can be very time consuming and might not be worth the few extra watts you might be able to save by doing so. Previously, the only alternative was simply to use the defaults. Therefore, Red Hat Enterprise Linux 6 includes separate profiles for specific use cases as an alternative between those two extremes, together with the tuned-adm tool that allows you to switch between these profiles easily at the command line. Red Hat Enterprise Linux 6 includes a number of predefined profiles for typical use cases that you can simply select and activate with the tuned-adm command, but you can also create, modify or delete profiles yourself.
To list all available profiles and identify the current active profile, run:
tuned-adm list
To only display the currently active profile, run:
tuned-adm active
To switch to one of the available profiles, run:
tuned-adm profile profile_name
for example:
tuned-adm profile server-powersave
To disable all tuning:
tuned-adm off
When you first install tuned, the default profile will be active. Red Hat Enterprise Linux 6 also includes the following predefined profiles:
- default
the default power-saving profile. It has the lowest impact on power saving of the available profiles and only enables CPU and disk plugins of tuned.
- desktop-powersave
- server-powersave
a power-saving profile directed at server systems. Enables ALPM powersaving for SATA host adapters, disables CD-ROM polling through HAL (refer to the hal-disable-polling man page) and activates the CPU and disk plugins of tuned.
- laptop-ac-powersave
a medium-impact power-saving profile directed at laptops running on AC. Enables ALPM powersaving for SATA host adapters, WiFi power saving, as well as the CPU, Ethernet and disk plugins of tuned.
- laptop-battery-powersave
a high-impact power-saving profile directed at laptops running on battery. It activates all power saving mechanisms from the previous profiles plus it enables the multi-core power-savings scheduler for low wakeup systems and makes sure that the ondemand governor is active and that AC97 audio power-saving is enabled. You can use this profile to save the maximum amount of power on any kind of system, not only laptops on battery power. The tradeoff for this profile is a noticeable impact on performance, specifically latency of disk and network I/O.
- throughput-performance
a server profile for typical throughput performance tuning. It disables tuned and ktune power saving mechanisms, enables sysctl settings that improve the throughput performance of your disk and network I/O, and switches to the deadline scheduler.
- latency-performance
a server profile for typical latency performance tuning. it disables tuned and ktune power saving mechanisms and enables sysctl settings that improve the latency performance of your network I/O.
All the profiles are stored in separate subdirectories under /etc/tune-profiles. So /etc/tune-profiles/desktop-powersave contains all the necessary files and settings for that profile. Each of these directories contains up to four files:
tuned.conf
the configuration for the tuned service to be active for this profile.
sysctl.ktune
the sysctl settings used by ktune. The format is identical to the /etc/sysconfig/sysctl file (refer to the sysctl and sysctl.conf man pages).
ktune.sysconfig
the configuration file of ktune itself, typically /etc/sysconfig/ktune.
ktune.sh
an init-style shell script used by the ktune service which can run specific commands during system startup to tune the system.
The easiest way to start a new profile is to copy an existing one. The laptop-battery-powersave profile contains a very rich set of tunings already and is therefore a useful starting point. Simply copy the whole directory to the new profile name like this:
cp -a /etc/tune-profiles/laptop-battery-powersave/ /etc/tune-profiles/myprofile
Modify any of the files in the new profile to match your personal requirements. For example, if you require the detection of CD changes you could disable that optimization by commenting out the appropriate line in the ktune.sh script:
# Disable HAL polling of CDROMS
# for i in /dev/scd*; do hal-disable-polling --device $i; done > /dev/null 2>&1
