Squeezing extra performance out of your hardware might sound like a pointless task given how cheap commodity upgrades are today. To a certain degree that is true — for most of us, it is cheaper to buy a new computer than to spend hours fighting to get a 5% speed boost. But what if the speed boost were 20%? How about if it were 50%?
The benefit you can get by optimizing your system varies depending on what kinds of tasks you are running, but there is something for everyone. Over the next few pages, we look at quick ways to optimize the Apache web server, both the GNOME and KDE desktop systems, both MySQL and PostgreSQL database servers, and more.
Before you start, you need to understand that optimization is not an absolute term: If you optimize a system, you improve its performance, but it is still possible it could further be increased. Getting 99.999% performance out of a system is not the objective because optimization suffers from the law of diminishing returns — the basic changes make the biggest differences, but after that it takes increasing amounts of work to obtain decreasing speed improvements.
Hard Disk
Many Linux users love to tinker under the hood to increase the performance of their computers, and Linux gives you some great tools to do just that. Whereas mothers tell us, "Don't fix what's not broken," fathers often say, "Fix it until it breaks." In this section, you learn about many of the commands used to tune, or "tweak," your file system.
Before you undertake any "under the hood" work with Linux, however, keep a few points in mind. First, perform a benchmark on your system before you begin. Linux does not offer a well-developed benchmarking application, but availability changes rapidly. You can search online for the most up-to-date information for benchmarking applications for Linux. If you are a system administrator, you might choose to create your own bench marking tests. Second, tweak only one thing at a time so that you can tell what works, what does not work, and what breaks. Some of these tweaks might not work or might lock up your machine.
Always have a working boot disk handy and remember that you are personally assuming all risks for attempting any of these tweaks.
Using the BIOS and Kernel to Tune the Disk Drives
One method of tuning involves adjusting the settings in your BIOS. Because the BIOS is not Linux and every BIOS seems different, always read your motherboard manual for better possible settings and make certain that all the drives are detected correctly by the BIOS. Change only one setting at a time.
Linux does provide a limited means to interact with BIOS settings during the boot process (mostly overriding them). In this section, you will learn about those commands.
Other options are in the following list, and are more fully outlined in the BOOTPROMPT HOWTO and the kernel documentation. These commands can be used to force the IDE controllers and drives to be optimally configured. Of course, YMMV (your mileage may vary) because these do not work for everyone:
► idex=dma — This forces DMA support to be turned on for the primary IDE bus, where x=0, or the secondary bus, where x=1.
► idex=autotune — This command attempts to tune the interface for optimal performance.
► idex=ata66 — If you have ATA66 drives and controllers, this command enables support for it.
► hdx=ide-scsi — This command enables SCSI emulation of an IDE drive. This is required for some CD-RW drives to work properly in write mode and it might provide some performance improvements for regular CD-R drives, too.
► idebus=xx — This can be any number from 20 to 66; autodetection is attempted, but this can set it manually if dmesg says that it isn't autodetected correctly or if you have it set in the BIOS to a different value (overclocked). Most PCI controllers are happy with 33.
► pci=biosirq — Some motherboards might cause Linux to generate an error message saying that you should use this. Look in dmesg for it; if you do not see it, you don't need to use it.
These options can be entered into /boot/grub/grub.conf in the same way as other options are appended.
The hdparm Command
The hdparm utility can be used by root to set and tune the settings for IDE hard drives. You would do this to tune the drives for optimal performance.
Once a kernel patch and an associated support program, the hdparm program is now included with Fedora. You should experiment only with the drives mounted read-only because some settings can damage some file systems when used improperly. The hdparm command also works with CD-ROM drives and some SCSI drives.
The general format of the command is this:
# hdparm command device
This command runs a hard disk test:
# hdparm -tT /dev/sda
You need to replace /dev/sda with the location of your hard disk. hdparm then runs two tests: cached reads and buffered disk reads. A good IDE hard disk should be getting 400-500MB/sec for the first test, and 20-30MB/sec for the second. Note your scores, and then try this command:
# hdparm -m16 -d1 -u1 -c1 /dev/sda
That enables various performance-enhancing settings. Now try executing the original command again — if you see an increase, you should run this command:
$ hdparm -m16 -d1 -u1 -c1 -k1 /dev/sda
The extra parameter tells hdparm to write the settings to disk so that they will be used each time you boot up — ensuring optimal disk performance in the future.
The man entry for hdparm is extensive and contains useful detailed information, but because the kernel configuration selected by Fedora already attempts to optimize the drives, it might be that little can be gained through tweaking. Because not all hardware combinations can be anticipated by Fedora or by Linux and performance gains are always useful, you're encouraged to try.
You can use the hdparm command to produce a disk transfer speed result with the following:
# hdparm -tT device
Be aware, however, that although the resulting numbers appear quantitative, they are subject to several technical qualifications beyond the scope of what is discussed and explained in this chapter. Simply put, do not accept values generated by hdparm as absolute numbers, but as only a relative measure of performance.
Systemwide tweaks to hdparm are formally handled through the /etc/sysconfig/harddisks files, but this file's use is poorly documented and, therefore, of little use.
You might find that your system turns off DMA for any CD-RW drives detected via a shell script command in rc.sysinit. This might not be appropriate for your hardware, so you can turn it back on simply by adding the line options ide-cd dma=1 to /etc/modules.conf.