Mini Shell

=== 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.
* For a server farm consolidating all physical machines on one bigger server and then using Virtualization.
* Enforce turning off machines that are not used (e.g. company policy).
* Try to establish a company culture that is Green "aware", including but not limited to the above point.
* Unplug and/or turn off peripherals that aren't used (e.g. external USB devices, monitors, printers, scanners).
* Turn off unused hardware already in BIOS.
* Disable power hungry features.
* Enable CPU scaling if supported for ondemand CPU governor. DO NOT 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 per 5 minutes
** echo "3000" > /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 / 
* 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 off monitor after 120s when X is running:
** xset dpms 0 0 120

=== Simple programmer tips for improving power usage ===
* Avoid unnecessary work/computation
* Use efficient algorithms 
* Wake up only when necessary/real work is pending
* Do not actively poll in programs or use short regular timeouts, rather react to events 
* If you wake up, do everything at once (race to idle) and as fast as possible
* 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)