FPS halves in FIFO/Immediate modes when moving cursor with direct scanout & CPU cursors

[Kam1k4dze]

systeminfo.txt

When I move the cursor in a Vulkan application running in FIFO or Immediate present mode—with both CPU-buffered hardware cursors and direct scanout enabled—the FPS drops to half the monitor's refresh rate. This doesn’t happen in Mailbox present mode.

Stationary cursor

Moving cursor

[vaxerski]

what if you disable DS?

[Kam1k4dze]

With DS disabled, the FPS is normal.

[fxzzi]

dyu have tearing enabled?

[Kam1k4dze]

Nope

[fxzzi]

Mind trying with tearing enabled? I think I'm having this issue too however it seems to fix itself with tearing enabled. Tested on Minecraft native wayland

[Kam1k4dze]

With tearing enabled:

• FIFO: FPS drops to roughly one-third of the monitor's refresh rate.
• Immediate: FPS drops to the monitor's refresh rate.
• Mailbox: FPS is four times lower when the cursor is moving (about 400 -> 100).

[Kam1k4dze]

Repro Case

Happens only on Nvidia

Prerequisites

• clang
• libc++
• ninja
• mangohud (optional for monitoring)

In your Hyprland config, enable direct scanout and hardware cursors. You can enable or disable tearing as you wish; the value to which your FPS drops when you move the cursor will differ, but the fact that you still experience an FPS drop remains.

cursor {
    no_hardware_cursors = false
    use_cpu_buffer = true
}
render {
    direct_scanout = true
    cm_enabled = false
}

Steps

1. Clone the repo

   git clone https://github.com/Kam1k4dze/dawn
   cd dawn

2. Configure with CMake

   cmake -S . -B out/Release \
     -G Ninja \
     -DCMAKE_BUILD_TYPE=Release \
     -DDAWN_FETCH_DEPENDENCIES=ON \
     -DBUILD_SAMPLES=ON \
     -DDAWN_USE_WAYLAND=ON \
     -DDAWN_USE_X11=OFF \
     -DCMAKE_C_COMPILER=clang \
     -DCMAKE_CXX_COMPILER=clang++ \
     -DCMAKE_CXX_FLAGS="-stdlib=libc++"

3. Build

   cmake --build out/Release

4. Run with MangoHud

   mangohud ./out/Release/Animometer --backend vulkan --present-mode fifo

[Kam1k4dze]

With

render {
    new_render_scheduling = true
}

FPS drops to 1/3 of the monitor refresh rate in FIFO mode