Gnome with 60hz display causes framerate issues

[solidv]

Is there an existing issue for this?

• I have searched the existing issues

Is your issue described in the documentation?

• I have read the documentation

Is your issue present in the latest beta/pre-release?

This issue is present in the latest pre-release

Describe the Bug

When using Gnome 50, if the display is set to 60hz i can't stream at stable 60fps. If i set the display to 120hz i can reach stable 60fps. This only happens with xdg portal, if i try 60hz display with KMS on gnome it works fine. Also in KDE i don't have this issue, i can reach stable 60fps even with display at 60hz. I'm streaming to a xbox series s.

Expected Behavior

No response

Additional Context

No response

Host Operating System

Linux

Operating System Version

Arch

Architecture

amd64/x86_64

Package

Linux - LizardByte/pacman-repo

GPU Type

AMD

GPU Model

9070XT

GPU Driver/Mesa Version

Mesa 26.0.4-arch2.2

Capture Method

XDG Portal Grab (Linux)

Apps

Log output

Online logs

No response

[psyke83]

I don't use GNOME daily, but I have done some testing related to this. I believe there are multiple issues at play here.

1. The kmsgrab capture method doesn't do any duplicate filtering. When you see a 60fps incoming rate, it doesn't reflect the active host framerate. The host could be running at a continuous 52fps, but the stream will always see 60fps due to the duplicates. One of the commits that currently part of fix: Resolve minimum_fps_target related issues on all platforms #4967 will introduce duplicate filtering to kmsgrab, but that commit may be split into another PR later.
2. GNOME 50's screencasting code doesn't support variable rate capture, so the maximum FPS it can send is currently limited to the host screen refresh rate. This may be part of the problem.
3. When the host framerate matches the stream framerate, mutter will not sustain the expected framerate when host-side vsync is disabled in games. In my testing, the portalgrab incoming rate would randomly degrade to ~52fps despite the on-screen FPS counter showing a solid 60fps. This actually applies to both kmsgrab and portalgrab capture, but because kmsgrab lies about the incoming framerate (point 1), you can only see this against stable/master by watching for stuttering rather than the reported framerate. Try enabling vsync and see if the issue improves.

[solidv]

i can't even get locked 60fps while in desktop. vsync didn't help, the framerate in moonlight xbox while gaming still flactuates between 57/58/59.