Optimise memory

Another easy way to give a performance boost to your system is to modify how swap space is used, or more precisely how the kernel favors swap over RAM.

vm.swappiness is a kernel parameter that controls how much the kernel favors swap over RAM. In other words, it is a parameter which sets the kernel's balance between reclaiming pages from the page cache and swapping out process memory. It is also defined as the tendency to steal mapped memory.

This variable kernel setting takes a value between 0 and 100. At 100, the kernel always prefers to find inactive pages and swap them out. With a value of 0, the system behaves so that applications that need memory can shrink the cache to a tiny fraction of RAM. Under Ubuntu the default setting for vm.swappiness is 60. To check this for yourself, type the command below into a console:

To modify this setting, simply open /etc/sysctl.conf with an editor and add the following line to the bottom of the file. You need root permissions to do this.

The lower the value of vm.swappiness the less the system will use swap space and the more data is cached to memory. We found 20 to be a good value for systems which have plenty of RAM (at least 1GB). If you don't have enough RAM, setting vm.swappiness too low will have an adverse impact on system performance.

Improve hard disk performance

If your system has a DMA-compatible (Direct Memory Access) hard disk you can improve performance with a couple of tweaks. Not only will these help the system boot more quickly but the tweaks also have the added benefit of improving the general speed of your system too.

You may know that the hdparm tool can be used to speed test your disk and change a few settings. It can also be used to optimise drive performance, and turn on some features that may not be enabled by default. However, we would advise to back up important data before experimenting with hdparm, as it can crash a computer and destroy data if a few parameters are misused.

To measure your hard disk data transfer speed and tweak the settings you need to install the hdparm utility using the Synaptic Package manager. Once installed, enter the following command:

These commands show the data transfer speed. Best to run them a few times to get an accurate idea of the speed.

Here is some typical output:

/dev/hda:
Timing cached reads: 1932 MB in 2.00 seconds = 966.63 MB/sec
Timing buffered disk reads: 118 MB in 3.02 seconds = 39.06 MB/sec

To improve performance by turning on DMA, start up a terminal and type:

(replace hda1 with the location of the boot partition; look at the output of the command df if you are unsure)

This command will need to be entered each time the system is started up, or you can modify your system so that this command is entered every time the machine boots up.

Currently all SATA hard drives automatically have DMA turned on, so there is no need to enable the -d1 flag. However, performance can still be improved by enabling read-ahead and write-caching.

Another way of improving hard disk performace is to turn off Automatic Acoustic Management (AAM). AAM is a method for reducing acoustic emanations. Since acoustic emanations are a byproduct of rotational speed, AAM provides a way to quiet a drive by limiting its rotational speed and power consumption—in effect, sacrificing performance for quieter operation. But if you are not concerned about noise, turning AAM off will slightly improve hard disk performance.

(replace hda1 with the relevant partition on your system)

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