Mouse polling rate
If you have invested in a high resolution mouse, adjusting the USB polling rate is a common trick to utilise the added precision it brings. The polling rate (or report rate) determines how often the mouse sends information to your computer. Measured in Hz, this setting equates to lag time (in ms).
By default, the USB polling rate is set at 125hz. The table below represents combinations of Hz values and their corresponding delay time:
If the polling rate is set at 125 Hz, the mouse cursor can only be updated every 8 milliseconds. In situations where lag is critical (for example games), it is useful to decrease this value to as little as possible. Increasing the polling interval will improve precision at the tradeoff of using more CPU resources, therefore care should be taken when adjusting this value.
Setting the polling rate
Here we are using the USBHID module of the kernel to set a custom "mousepoll" rate. Simply add the following line to your /etc/modprobe.conf file:
options usbhid mousepoll=[polling interval]
(where [polling interval] is a number in ms from the table above. For example, to set a polling rate of 500Hz:
options usbhid mousepoll=2
Now, to ensure the USBHID module loads upon boot add the following to your /etc/rc.conf file, within the MODULES list:
Displaying current mouse rate
A tool exists (named evhz) that can display the current mouse refresh rate -- useful when checking that your customised polling settings have been applied.
Compile it with:
gcc -o evhz evhz.c
Then execute in root:
Alternatively, Windows tools such as DirectX mouserate checker can be run using WINE.
CS:S Mouse Optimization Guide -- largely aimed at Windows users, though the same principles apply for Linux.
HOWTO Customize Mouse Polling Rate -- from Gentoo wiki