I feel that input latency should be as minimal as possible. Input latency affects the game feel and is especially important when the game requires fast reactions, such as fast-paced multiplayer FPS game or racing sim.
I’m currently working on a project with custom game engine where low input latency is important. I take input latency seriously and do my best to minimize it. One part of minimizing input latency is to make the frame rendering as fast as possible.
How to minimize input latency
In order to minimize input latency, the game needs to postpone the frame’s input processing as late as possible before frame present. Also the game should only have single buffered present.
Naively by default, games use triple buffering. Triple buffering is best choice when smoothness and larger frametime budget is required. For example, when using single buffered present with 60hz screen, both the CPU and GPU must have computed the frame under 16.6ms to be ready for the next vblank.
When using double or triple buffering, both GPU and CPU have 16.6ms of time to process the frame, giving the best throughput with cost of additional latency. Thus single buffered rendering reduces the system parallelization. CPU has to wait for GPU to complete the present and then GPU has to wait for CPU to start pushing rendering commands.
In my current project, I use single buffered rendering. The game waits for GPU to complete present before processing input for next frame. This achieves theoretical input latency between 16.6ms – 33.2ms on 60hz refresh rate.