Tuning Device Driver Options

Some device drivers support options. For instance, Figure 15.4 shows the SCSI Low-Level Drivers submenu of the SCSI Device Support menu, highlighting the SYM53C8XX SCSI Support option. When you activate this option, using either M or Y, the configuration tool presents a number of additional options that can fine-tune the driver's behavior.

Figure 15.4: Some kernel options provide associated sub-options that fine-tune the driver's behavior.

Precisely what these options do is highly device-specific. Some of the possibilities include:

Activating Advanced Features Some device features are on the cutting edge, as far as the Linux driver is concerned. Such features may enhance performance, but because they're so new, they may also cause system crashes or other problems. Such options are usually marked as being new or experimental. Other features may improve performance and be reliable with some hardware, but some specific models of devices may not support the option.

Adjusting Parameters for Specific Devices Some drivers support a wide array of devices, and the driver might work best with some tuning adjustments for specific devices. For instance, you might adjust the speed of the device or select an option that tunes assorted internal parameters based on the subclass of the device you're using.

Enabling Compatibility Modes Some hardware supports both device-specific and more generic methods of operation. Ordinarily, the device-specific modes work best, but these modes may cause problems for some specific devices. For this reason, some drivers give you the option of using an older mode that works with more devices, albeit with a drop in speed.

Enabling Debugging Features Some drivers support special debugging options. These may log extra information in the kernel message queue (accessible by typing dmesg) or in special files in the /proc filesystem, which can be useful if you're having problems. On the other hand, this activity is almost certain to degrade performance.

When you activate a driver, look for any driver-specific options that may be present. If it's not obvious what these options do, examine the help for each option. (If you use make xconfig for a 2.5.x or 2.6.x kernel, the help information appears in the lower-right pane. For 2.4.x or earlier kernels or if you use make menuconfig, you need to select the Help option.) In most cases, this description will provide guidance concerning how to pick the best option, although sometimes the descriptions can be confusing. If in doubt, leave the option set at its default value or pick what sounds like the more conservative option. Alternatively, you can experiment, selecting one option and using it and then trying the other option.

Team LIB

1 previous

0 0

Post a comment