Linux Performance Tuning for the Faint of Heart

Recompiling your Linux kernel might not be as scary as you think. Clarence Smith gives us a good step-by-step process for building your own customized kernel.
Configuring the Kernel

Now, from within /usr/src/linux, type make config. You are now prompted to answer many questions about your system. If you say you don't have hardware that you do have, that particular hardware will not be supported by the new kernel. Likewise, if you say you have hardware that you don't have, you will waste memory. Also, you want to enable only the software features that you are going to use.

I will attempt to point out some of the most significant configuration questions. One of the first questions is:

'Kernel math emulation' CONFIG_MATH_EMULATION ?

If you don't have a math co-processor, you should answer this question YES. Those who do have a math co-processor chould answer NO. A kernel with math-emulation compiled in it will still use the processor if one is present. The math-emulation simply won't get used in that instance. This will result however in a somewhat larger kernel and a waste of memory.

There are a couple of questions about hard disk support. One in particular can cause a bit of confusion:

'XT harddisk support' CONFIG_BLK_DEV_XD

I answer this question NO. This really doesn't have to do with hard disks—it has to do with your controller card. AT controller cards are 16-bit cards supported by the standard hard disk driver. XT controller cards are 8-bit cards that are very rare in 386-class machines.

'TCP/IP networking' CONFIG_INET :

Answer YES if you plan to have your system interactive on the net. This includes SLIP and PPP connections. Answer NO if you aren't going to connect to the net right now; you can always compile another kernel later.

'System V IPC' CONFIG_SYSVIPC :

This isn't used for many things, but doesn't use much memory. YES is recommended.

'Use -m486 flag for 486-specific optimizations' CONFIG_M486 :

If you have an i386 system, answer NO. Otherwise you should select YES. This uses a little bit of memory. Adding this flag will not slow a 386 down, other than using extra memory, but will speed up a 486 quite a bit.

Types of Devices

There are a series of questions which have to do with different types of SCSI drivers and interfaces. If you have a SCSI controller, then you would want to enable the drivers via the configuration process. For those who don't have a SCSI controller, select NO, and move on to the next step in the configuration. If you don't select SCSI support, you won't be asked whether or not to include SCSI devices.

Network device support mainly has to do with selecting the proper Ethernet device or other network connection. PPP and SLIP are used to connect to TCP/IP networks over the serial port; PLIP is used to connect TCP/IP networks over the parallel port, and the rest are ethernet controllers. Do not select drivers of devices you do not have. This can sometimes cause conflict later when you are booting.

Another important section in the kernel config process has to do with the different filesystems. There is an advantage to compiling the kernel to have only the filesystems you need. There are several different filesystems supported by Linux:

'Standard (minix) fs support' CONFIG_MINIX_FS :

This is the original Linux filesystem. It is considered to be one of the more stable filesystems, and is still widely used. You probably want this unless you are really desperate for space or will really never use it.

'Extended fs support' CONFIG_EXT_FS :

Only select this if you still have filesystems from the 'old days' that will use this precursor of the second extended filesystem. This filesystem is slow and no longer actively maintained. It is there only for backwards compatibility. NO.

'Second extended fs support' CONFIG_EXT2_FS :

The ext2 filesystem is the most 'full-featured' of the filesystems. It is a super rewrite of the original extended filesystem, with improved speed as well. This is by far the most popular filesystem. A filesystem debugging package is available for this filesystem that can help you recover from fairly bad filesystem crashes. YES.

'xiafs filesystem support' CONFIG_XIA_FS :

This is a modification of the Minix filesystem (allowing for such things as longer filenames). If you plan to use it (YES), otherwise (NO).

'msdos fs support' CONFIG_MSDOS_FS :

This filesystem allows for access to the FAT filesystem used by MS-DOS. It is a great advantage for those who need to access floppies or hard disk partitions that use that filesystem. In addition, if you use the UMSDOS filesystem (usually because you installed Linux on an MSDOS partition), you need to include MSDOS filesystem support.

'/proc filesystem support' CONFIG_PROC_FS :

The PROC filesystem does not touch your disk. It is used by the kernel to provide data kept within the kernel itself to system programs that need that information. Many standard utilities will not function without this filesystem. YES.

'NFS filesystem support' CONFIG_NFS_FS :

The NFS filesystem is necessary for those who have a physical network and need to mount NFS filesystems from other computers. If you are on a TCP/IP network, you probably want this option. Otherwise, you don't.

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