Arch Linux

Celsiuss

Member

Registered: 2020-11-05

Posts: 17

Stuttering/uneven framerate on external monitor with ThinkPad T16

My external monitor (Dell U4924DW) is set to 60 Hz refresh rate. However, the entire DE is stuttering slightly every half a second or so. This is noticeable by just moving the mouse. glxgears reports an average framerate of 54 FPS.
I tried decreasing the refresh rate from 60 to 30, but the same issue is still present, instead of a solid 30 FPS I get 27-28.
Decreasing the resolution does not help.

The monitor is connected through USB type C (DP), however, switching to HDMI did not help at all.
The eDP display is running stable.

The laptop is a ThinkPad T16 gen 2 with an AMD 7840U CPU with integrated Radeon 780M Graphics.
Running latest KDE Plasma 6.2.4 under Wayland.
linux 6.12.3

Some inxi info:

System:
  Kernel: 6.12.3-arch1-1 arch: x86_64 bits: 64 compiler: gcc v: 14.2.1
    clocksource: tsc
  Desktop: KDE Plasma v: 6.2.4 tk: Qt v: N/A wm: kwin_wayland vt: 2 dm: SDDM
    Distro: Arch Linux
Machine:
  Type: Laptop System: LENOVO product: 21K7CTO1WW v: ThinkPad T16 Gen 2
    serial: <superuser required> Chassis: type: 10 serial: <superuser required>
  Mobo: LENOVO model: 21K7CTO1WW serial: <superuser required>
    part-nu: LENOVO_MT_21K7_BU_Think_FM_ThinkPad T16 Gen 2
    uuid: <superuser required> UEFI: LENOVO v: R2FET58W (1.38 )
    date: 07/19/2024
Battery:
  ID-1: BAT0 charge: 85.5 Wh (98.4%) condition: 86.9/86.0 Wh (101.0%)
    volts: 17.5 min: 15.5 model: Sunwoda 5B11M90039 type: Li-poly
    serial: <filter> status: not charging cycles: 11
CPU:
  Info: 8-core model: AMD Ryzen 7 PRO 7840U w/ Radeon 780M Graphics bits: 64
    type: MT MCP smt: enabled arch: Zen 4 rev: 1 cache: L1: 512 KiB L2: 8 MiB
    L3: 16 MiB
  Speed (MHz): avg: 400 min/max: 400/5132 boost: enabled cores: 1: 400
    2: 400 3: 400 4: 400 5: 400 6: 400 7: 400 8: 400 9: 400 10: 400 11: 400
    12: 400 13: 400 14: 400 15: 400 16: 400 bogomips: 105436
  Flags: avx avx2 ht lm nx pae sse sse2 sse3 sse4_1 sse4_2 sse4a ssse3
Graphics:
  Device-1: Advanced Micro Devices [AMD/ATI] Phoenix1 vendor: Lenovo
    driver: amdgpu v: kernel arch: RDNA-3 pcie: speed: 16 GT/s lanes: 16 ports:
    active: DP-1,eDP-1 empty: DP-2, DP-3, DP-4, DP-5, DP-6, HDMI-A-1,
    Writeback-1 bus-ID: 64:00.0 chip-ID: 1002:15bf class-ID: 0300 temp: 49.0 C
  Device-2: Syntek Integrated Camera driver: uvcvideo type: USB rev: 2.0
    speed: 480 Mb/s lanes: 1 bus-ID: 3-1:2 chip-ID: 174f:11a8 class-ID: fe01
    serial: <filter>
  Display: wayland server: X.org v: 1.21.1.14 with: Xwayland v: 24.1.4
    compositor: kwin_wayland driver: X: loaded: modesetting
    alternate: fbdev,vesa dri: radeonsi gpu: amdgpu d-rect: 7040x2640
    display-ID: 0
  Monitor-1: DP-1 pos: primary,top-left res: 5120x1440 size: N/A modes: N/A
  Monitor-2: eDP-1 pos: bottom-r res: 1920x1200 size: N/A modes: N/A
  API: EGL v: 1.5 hw: drv: amd radeonsi platforms: device: 0 drv: radeonsi
    device: 1 drv: swrast gbm: drv: kms_swrast surfaceless: drv: radeonsi
    wayland: drv: radeonsi x11: drv: radeonsi
  API: OpenGL v: 4.6 compat-v: 4.5 vendor: amd mesa v: 24.3.1-arch1.2
    glx-v: 1.4 direct-render: yes renderer: AMD Radeon 780M (radeonsi
    gfx1103_r1 LLVM 18.1.8 DRM 3.59 6.12.3-arch1-1) device-ID: 1002:15bf
    display-ID: :0.0
  API: Vulkan v: 1.4.303 layers: 4 surfaces: xcb,xlib,wayland device: 0
    type: integrated-gpu driver: N/A device-ID: 1002:15bf
Info:
  Memory: total: 32 GiB note: est. available: 29.02 GiB used: 8.8 GiB (30.3%)
  Processes: 410 Power: uptime: 40m states: freeze,mem,disk suspend: s2idle
    wakeups: 0 hibernate: platform Init: systemd v: 256 default: graphical
  Compilers: gcc: 14.2.1 Shell: Zsh v: 5.9 running-in: alacritty
    inxi: 3.3.36

Update:
Disabling the built-in screen makes the external monitor perform as expected, so it seem the issue is caused by having two displays active at once. Not sure what the cause of this is, but would appreciate any pointers here.

Last edited by Celsiuss (2024-12-09 14:08:39)