X.Org/Modelines

From Gentoo Linux Wiki

Setting modelines can reduce blanking, that is, the blanking time between the transmission of two lines to the monitor will be reduced. For CRT, this time is necessary as the electron beam cannot move instantly back to the beginning for drawing the next line. The X-server might not always detect the monitor modelines via EDID that that are available. To generate the modelines we use the cvt program(part of x11-base/xorg-server).

Start with generating the modeline:

Replace X with the horizontal resolution (multiple of 8 required), Y with the vertical resolution, and refresh with the refresh rate.

A typical modeline for 1280x1024@60Hz looks like:

# 1280x1024 59.79 Hz (CVT 1.31M4-R) hsync: 63.02 kHz; pclk: 90.75 MHz
Modeline "1280x1024R"   90.75  1280 1328 1360 1440  1024 1027 1034 1054 +hsync -vsync

Now add to /etc/X11/xorg.conf:

...
Section "Monitor"
    ...
    Option         "ReducedBlanking" "True"
    # 1280x1024 59.79 Hz (CVT 1.31M4-R) hsync: 63.02 kHz; pclk: 90.75 MHz
    Modeline "1280x1024R"   90.75  1280 1328 1360 1440  1024 1027 1034 1054 +hsync -vsync
    ...
EndSection

Section "Screen"
    ...
    Subsection "Display"
        ...
        Modes "1280x1024R"
        ...
    EndSubsection
    ...
EndSection
....

Restart your X Server for the changes to take effect.