A few options may increase performance by up to 30 percent (or more) over the default. Set them in /etc/X11/xorg.conf. However, you will first need to check that your motherboard and video card support these options.

First, let's see if your video card can support fast writes. We'll do this by closely inspecting the output from lspci. Specifically, we are looking at the "VGA compatible controller" information.

Code Listing 6.1: Video card check

# lspci -vv

01:00.0 VGA compatible controller: ATI Technologies Inc Radeon Mobility M6 LY (prog-if 00 [VGA])

. . .

Capabilities: [58] AGP version 2.0

    Status: RQ=48 Iso- ArqSz=0 Cal=0 SBA+ ITACoh- GART64- HTrans- 64bit- FW+ AGP3- Rate=x1,x2,x4

While quite a lot of information is produced, we are looking for FW in the "Status" subsection of the AGP "Capabilities" section. If FW+ is present in the "Status" line, it means the card supports fast writes. We can now check if the motherboard supports fast writes.

Important: If you do not see FW+, but instead see FW-, you cannot enable fast writes in xorg.conf. Your card does not support fast writes.

Now let's make sure the motherboard supports fast writes as well. This time, look at the "Host bridge" section of your lspci output.

Code Listing 6.2: Motherboard check

# lspci -vv

00:00.0 Host bridge: Intel Corporation 82830 830 Chipset Host Bridge (rev 02)

. . .

Capabilities: [a0] AGP version 2.0

    Status: RQ=32 Iso- ArqSz=0 Cal=0 SBA+ ITACoh- GART64- HTrans- 64bit- FW+ AGP3- Rate=x1,x2,x4

Again, examine the "Status" subsection of your AGP "Capabilities" section. Look for FW. If you see FW+, your motherboard supports fast writes.

Important: Remember, both your video card information and your motherboard information must show the same FW capability. If either device shows FW- in "Status", you cannot enable fast writes in xorg.conf.

Assuming that all has gone well and both your motherboard and video card support fast writes, let's enable this option in /etc/X11/xorg.conf and get the best performance out of your hardware.

Code Listing 6.3: xorg.conf

Section "Device"

  Option     "AGPMode" "4"

  (This increased FPS from 609 to 618.)

  Option     "AGPFastWrite" "True"

  (This had no measurable effect, but it may increase instability of your computer.)

  (You may also need to set it in your BIOS.)

  Option     "EnablePageFlip" "True"

  (This improved FPS from 618 to 702. It also is "risky" but few people have reported problems.)

  ...

EndSection

Warning: Enabling AGPFastWrite on a VIA chipset will very likely cause your machine to lock up. VIA chipsets do not play nicely with fast writes, so use this setting at your own risk.

Note: Remember, if you want fast writes to work properly, you will have to first enable the appropriate option in your BIOS.

If you want to set even more features, check out the feature matrix on the DRI web site or the features listing on Sourceforge.