Higher Helldivers 2 FPS on external monitor than internal display

Framework Laptop 16 Linux
2

I’ve done a lot of testing on this and I think I can provide some insights.

  1. Displaying at a lower resolution yields better performance, even if the game’s render resolution is the same. The simple act of sending more pixels over the display connection, regardless of what resolution the game is rendering at, has an impact on memory bandwidth that is wildly underrepresented in gaming benchmarks. This is much easier to detect on a hardware limited device like the Steam Deck, but I’ve also checked and seen this behavior on the Framework 16. When you say “both 2560x1600 and 1920x1200” are you changing the display’s resolution or the game’s render resolution? If it’s the game render resolution, then you are not eliminating this factor. For example: let’s say your playing a game and the game’s resolution is set to 720p. You have two monitors to choose from, one that outputs at 4k and one that outputs at 1080p. Outputting to the 4k will likely have lower fps than the 1080p display even though the game’s render resolution hasn’t changed. There also seems to be a slight impact based on the dock in use, as I can see slightly different frame rates when I switch docks in testing.
  2. If you connect to one of the expansion cards for video out rather than the dGPU directly, video has to be piped through the iGPU and this has a performane impact like you say. Personally, I prefer to use the expansion cards anyways, as the dGPU port seems to have it’s own issues as well.

On some devices, these fps differences can be quite drastic.

Also, by allowing the monitor itself to upscale from display resolution to the monitor’s maximum hardware supported resolution, there’s technically some processing taken off of the device. On something like the steam deck, this can be a significant performance increase depending on the amount of scaling needed.

Using Fullscreen instead of borderless can help avoid some of this by skipping the compositor and displaying direct to display, but idk if fps overlays and such will negate that.

Side note: I’ve got a similar thread here: FPS loss when gaming on external monitor - Framework Laptop 16 - Framework Community

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