I am a Manjaro/Arch user who games frequently and I think I may have a possible solution for you! As my distro (Manjaro 17.1.1-KDE) doesn't have a sensitivity slider anywhere, I'm assuming this is a 1:1 input. It certainly feels like one to me. Anyways, read on.
You do not need to run these commands as root.
As with all versions of Linux, your mileage may vary. This was done using Manjaro/Arch 17.1.1 with KDE.
You will need to determine if you're using Wayland or X11 by running two commands. If you already know that you're using X11, you can skip these two commands.
The first command is:
loginctl
The second command is:
loginctl show-session <YOUR_NUMBER> -p Type
Replace <YOUR_NUMBER> with the number listed under "SESSION" that was given after running the first command. If you're running Wayland, this guide won't help you. But if you have X11, the fix is pretty simple. I borrowed this method from this website.
So now that we've determined you're on X11, here's how you do this:
Use the "xset" command to modify your system's mouse acceleration settings by running the following command:
xset m 0 0
If this messes everything up, don't panic! You can always replace the "0 0" with "default" to restore default settings.
A good way to apply this setting at login is to copy and paste the following code into a ".desktop" file and save that in your home folder's "./config/autostart/" folder:
[Desktop Entry]
Name=Disable mouse acceleration
Exec=xset m 0 0
Type=Application
All of this information came from the Arch wiki. They explain the commands in greater detail there. I recommend taking a look if you're interested in finding out specifically what the xset command does.
As far as setting mouse DPI goes, that will be handled through a driver. If you're like me and have a mouse that doesn't have a Linux driver, but does have on-board profile storage, you could try plugging the mouse into a Windows PC that has the driver, setting your mouse the way you'd like, then saving the settings to your mouse's on-board storage. That, or maybe having Windows in VirtualBox would work.
Hopefully this guide was easy enough to follow. When I was a Linux newbie, guides with awful formatting and guides that assumed I knew some basic things were the death of me, so I'm trying not to repeat those mistakes. My apologies if this is considered reviving a dead thread. I spent a long time trying to figure out how this is done to no avail, but now that I've figured it out I really want to share it so others don't have to spend as much time as I did.