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Revision as of 13:19, 6 August 2009 by Pknirsch (talk | contribs) (Release Notes)

Power Management improvements for Fedora 12


Our goal is the improvement of power management especially in regard to userland. This project is based on measurement and statistic of power consumption mainly on laptops. We are trying to locate the main power greedy applications by measuring with new tools, which have been introduced in our project. For Fedora 12 the plan is to improve and extend the functionality of tuned, merge it with ktune from RHEL 5 and introduce a new and easy way to switch between various predefined and extendible tuning settings for your system.


  • Phil Knirsch <> (Lead, tuned, monitoring, documentation)
  • Jiri Skala <>(BLTK packager, pm-utils maintainer)
  • Marcela Maslanova <> (system profile switcher)
  • Petr Lautrbach <> (scomes, system profile switcher)
  • Jan Scotka <> (QA coverage)
  • Karel Volny <> (QA coverage)

Current status

  • Targeted release: Fedora 12
  • Last updated: 07/30/09
  • Percentage of completion: 90%

Detailed Description

With Fedora 11 we introduce a new daemon called tuned. The goal now is to extend it's functionality and merge it with a tool we developed for Red Hat Enterprise Linux 5 called ktune as well as introduce a new and easy way to switch between various predefined and extendible tuning settings for your system.

Of course auditing wakeups and disk/network IO is still ongoing for Fedora 12 as well.

Benefit to Fedora

Simple: On average use less power for turned on machines while not affecting user experience (a lot ;)).


  • Review and fix behaviour of typical applications in a full installed Fedora in regard to: [IN PROGRESS]
    • CPU wakeups
    • Disk IO
    • Network IO
  • Extend tuned
    • Integration of ktune and tuned: Static vs. dynamic tuning parts + performance vs. power tuning options [90% DONE (needs more testing)]
    • New monitoring and tuning plugin for CPUs (using PM-QOS for CPUs) [100% DONE]
    • New disk tuning algorithm for a more gradual tuning [90% DONE (needs more testing)]
  • System tuning configuration and profiles [90% DONE (needs more testing)]
    • Introduce new CLI to allow switching between various predefined settings
    • Allow creating / editing / deleting profiles
  • New tool to measure improvements to system configuration changes or application changes: [100% DONE]

Test Plan

  • For "Extended tuned"
    • yum install tuned
    • service tuned start
    • cpu, disk and net devices should adapt to usage (monitor using strace e.g.)**
    • If ktune is enabled check if the system settings for the current profile are being applied and restored when stopping the service
  • For "System tuning configuration and profiles"
    • Run the new system tuning tool and list the different available profiles using:
      • tuned-adm list
    • Run the new system tuning tool and select one of the profiles. Restart the machine afterwards and make sure the profile is being used at startup
      • tuned-adm modes laptop-battery-powersave
      • tuned-adm modes default
      • tuned-adm modes throughput-performance
  • For "New tool to measure improvements to system configuration changes or application changes"
    • yum install tuned-utils
    • run scomes
    • change system settings
    • run scomes again
    • compare restults

User Experience

As power saving is not really visible without a measuring it the effects will not be directly visible. So in order to really see the effect you'll either need a laptop and run that on battery power or a wattmeter that is hooked between your system and the power line.


tuned base package now requires kobo for the tuned-adm tool.

Contingency Plan

Need to make sure to test the more aggressive power saving features if they break on common hardware and back it out in case they do or make some form of black/whitelist for know cases.


Simple user tips for improving power usage

  • Use a properly dimensioned system for the job (no need for overpowered systems for simple Desktop use e.g.)
  • For servers consolidate services on fewer systems to maximize efficiency of each system
  • Enforce turning of systems that are not used (e.g. company policy)
  • Unplug and/or turn of peripherals that aren't used (e.g. external USB devices, monitors, printers, scanners)
  • Turn of unused hardware already in BIOS.
  • Disable power hungry features.
  • Enable CPU scaling if supported for ondemand CPU governor. DONT use powersave governor, typically uses more power than ondemand (race to idle).
  • Put network card to 100 mbit/10 mbit:
    • 10 mbit: ethtool -s eth0 advertise 0x002
    • 100 mbit: ethtool -s eth0 advertise 0x008
    • Doesn't work for every card
  • Put harddisk to spindown fast and full power saving:
    • hdparm -S240 /dev/sda (20m idle to spindown)
    • hdparm -B1 /dev/sda (Max powersave mode)
  • Make sure writes to hd don't wake it up too quickly:
    • Set flushing to once every 5 minutes
    • echo "30000" > /proc/sys/vm/dirty_writeback_centisecs
    • Enable laptop mode
    • echo "5" > /proc/sys/vm/laptop_mode
  • Use relatime for your / partition
    • mount -o remount,relatime /
  • Disable CD-ROM polling from HAL (prevents popups when a CD is inserted):
    • hal-disable-polling --device /dev/scd0
  • Enable USB autosuspend by adding the following to the kernel boot commandline:
    • usbcore.autosuspend=5
  • Screensaver needs to dpms off the screen, not just make colors black. To turn of monitor after 120s when X is running:
    • xset dpms 0 0 120

Simple programmer tips for improving power usage

  • Wake up only when necessary
  • Do not poll in programs or use short regular timeouts, rather react to events
  • If you wake up, do everything at once (race to idle)
  • Use large buffers to avoid frequent disk access. Write one large block at a time
  • Don't use [f]sync() if not necessary
  • Group timers across applications if possible (even systems)
  • After using lots of malloc() and free() calls run malloc_trim(0) once (unportable)


Release Notes

In order to allow users to monitor the behaviour of their systems and to improve power consumption in general, several improvements were done for Fedora 12:

  • Improved tuned service to dynamically adapt system settings to the current use
  • New static tuning service available called ktune as part of tuned
  • New configuration switch commandline tool called tuned-adm

Users of Fedora 12 should therefore see a reduction in power usage of their system.

Comments and Discussion