Mouse acceleration settings typically can be configured using tools provided by your desktop environment. Alternatively, Xorg supplies similar methods more directly, using the xset command. Along with sensitivity, your mouse speed is controlled by acceleration and threshold levels. The command synopsis is
xset m acceleration threshold.
xset m 4 1
Acceleration defines how many times faster the cursor will move than the default speed, when the cursor moves more than threshold pixels in a short time. Acceleration can be a fraction, so if you want to slow down the mouse you can use 1/2, and if 3 is slightly too fast, but 2 is too slow, you can use 5/2. You effectively disable the threshold by setting it to 1, that way the cursor will always move the same speed. To get the default settings back, type
xset m default.
Disabling mouse acceleration
Mouse acceleration can be disabled using:
xset m 0 0
Query currently used settings
The current acceleration/threshold settings can be checked using:
xset q | grep -A 1 ^Pointer
Making changes permanent
You can add the xset command to your ~/.xinitrc to get the desired mouse speed every time X starts.
For more info see