Laptop mode is used to minimize the time that the hard disk needs to be spun up, to conserve battery power on laptops. It has been reported to cause significant power savings.
Laptop mode is controlled by the knob /proc/sys/vm/laptop_mode. This knob is present for all kernels that have the laptop mode patch, regardless of any configuration options. When the knob is set, any physical disk I/O (that might have caused the hard disk to spin up) causes Linux to flush all dirty blocks. The result of this is that after a disk has spun down, it will not be spun up anymore to write dirty blocks, because those blocks had already been written immediately after the most recent read operation. The value of the laptop_mode knob determines the time between the occurrence of disk I/O and when the flush is triggered. A sensible value for the knob is 5 seconds. Setting the knob to 0 disables laptop mode.
To increase the effectiveness of the laptop_mode strategy, the laptop_mode control script increases dirty_expire_centisecs and dirty_writeback_centisecs in /proc/sys/vm to about 10 minutes (by default), which means that pages that are dirtied are not forced to be written to disk as often. The control script also changes the dirty background ratio, so that background writeback of dirty pages is not done anymore. Combined with a higher commit value (also 10 minutes) for ext3 or ReiserFS filesystems (also done automatically by the control script), this results in concentration of disk activity in a small time interval which occurs only once every 10 minutes, or whenever the disk is forced to spin up by a cache miss. The disk can then be spun down in the periods of inactivity.
If you want to find out which process caused the disk to spin up, you can gather information by setting the flag /proc/sys/vm/block_dump. When this flag is set, Linux reports all disk read and write operations that take place, and all block dirtyings done to files. This makes it possible to debug why a disk needs to spin up, and to increase battery life even more. The output of block_dump is written to the kernel output, and it can be retrieved using “dmesg”. When you use block_dump and your kernel logging level also includes kernel debugging messages, you probably want to turn off klogd, otherwise the output of block_dump will be logged, causing disk activity that is not normally there. More interested users should look laptop mode up in www.kernel.org, the big daddy of all linux distribution. (or mommy, not too sure!)
Install Laptop Mode tools:
Quite easy, just do the following and you’re done.
Enable Laptop mode to save power and lower CPU temp:
Replace the number with 5.
Save and exit. Now reboot. Enjoy.