FS-UAE can be used with variable refresh rate hardware:
This allows for smooth and even rendering of the Amiga display, similar to classic v-sync, but with lower latency, and without the occasional hiccups due to missing a frame.
If you can afford it, I highly recommend getting a setup with G-SYNC or FreeSync for FS-UAE (and other emulators). This is definitively the best way to experience FS-UAE.
Due to the way variable refresh rate work and based on experience, you get most reliable results when your desktop refresh rate is higher than the refresh rate of the emulated system.
So for example, if you want to emulate both 50/60 Hz systems, your desktop refresh rate should be more than 60 Hz, for example 85 Hz. But you can also just go as high as your monitor allows, for example 144 Hz. The important thing is to use > 60 Hz (or > 50 Hz if you only want to emulate PAL systems).
Note, when you want to visually verify that G-SYNC / FreeSync is working (see the next section), any stuttering due to it not working will be more obvious with a lower refresh rate, so 85 Hz is a quite good one for this purpose.
The best way to see if G-SYNC / FreeSync is actually working is to use your eyes. Start the emulator with a game / program which scrolls with constant speed. For example:
War Zone (1991)(Core)[cr Flashtro][t +26 Flashtro]
This cracktro has a horizontally scrolling text with fixed speed. If you run in windowed mode, you should see micro-stuttering (uneven movement of the scrolling text). When you change to fullscreen, if G-SYNC / FreeSync is working properly, the scrolling should be perfectly smooth in comparison.
In general, variable refresh rate will only work in fullscreen (when FS-UAE covers the entire X display). This means that you must likely only have one monitor enabled in a multi-monitor setup, and you cannot have any overlapping windows (for example, desktop notifications appearing will temporarily disable variable refresh rate).
Use NVIDIA X Server Settings to enable "Allow G-SYNC/G-SYNC Compatible" under OpenGL Settings.
To verify that G-SYNC is working/enabled, you can also enable "Enable G-SYNC/G-SYNC Compatible Visual Indicator" which adds a green G-SYNC logo in the upper right corner of the screen when FS-UAE is running and G-SYNC is active.
Please note that G-SYNC will only work (at the time of this writing) of you have a single monitor enabled. If you have more than one monitor, disconnect the other one(s) before running FS-UAE. Just disabling the other monitors should also work, but the author has experienced stuttering every few seconds when other monitors are connected, even if they are disabled.
Please make sure you have Linux kernel 5.0 and greater. You need to modify
your Xorg configuration to enable freesync. Create a file called
(create /etc/X11/xorg.conf.d/ if needed) with the content:
Section "Device" Identifier "AMD" Driver "amdgpu" Option "DRI" "3" Option "VariableRefresh" "true" EndSection
To verify that variable refresh rate is enabled, you can check the output
xrandr --prop, you should see something like this:
... DisplayPort-1 connected primary 1920x1080+0+0 [...] ... vrr_capable: 1 range: (0, 1)
If your connected display supports FreeSync, you should see vrr_capable: 1.
Additionally, to check that variable refresh rate is enabled in the driver, you can check for the following line in $HOME/.local/share/xorg/Xorg.0.log:
AMDGPU(0): VariableRefresh: enabled
At the time of writing, the author is not aware of support for variable refresh rate in macOS.