Regression in 3.8.28: GPU usage hits ~100% in 4K video playback and ~30W draw at idle on AMD desktops (RX 9070 XT, similar on Vega 8)

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issue の種類
バグ
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おおむね明確
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活発
技術スタック
linux
領域
performance

調査の方向性

The payload names no source files, tests or entry points, and this repository is a community tracker without code. The work is to reproduce the regression on an AMD GPU under SteamOS 3.8.28 and compare the performance overlay readings (GPU usage, clock, power) with the previous release, then identify whether the driver stack or Gamescope changed. Done means a reproducible diagnosis that points to a specific component, which needs hardware access and maintainer input.

索引モデルが issue の本文から書いたものです。

説明

systems information
Steam Forge: Ryzen 7 9800X3D, ASUS Prime RX 9070 XT 16GB, MSI MAG X870 Tomahawk WiFi, 32GB DDR5-5600, 4TB NVMe. SteamOS is the primary OS, with a separate 128GB NVMe holding EndeavourOS. (Gaming pc)

Steam Kettle: Ryzen 7 5700G with integrated Vega 8 graphics, MSI B550M PRO-VDH WiFi, 16GB DDR4, 512GB NVMe, 4GB UMA frame buffer, Secure Boot disabled. (Media pc)

•	Steam client version: Build date Tue, October 13, 2026 1:44pm
•	SteamOS version: 3.8.28 (Stable)
•	Opted into Steam client beta?: [No]
•	Have you checked for updates in Settings > System?: Yes

Please describe your issue in as much detail as possible:

Expected: 4K video playback should use mostly the hardware decoder with low GPU load, and idle power should stay low, as it did before the update.

What happened: After updating to SteamOS 3.8.28, two separate desktop PCs show high GPU usage during video playback. One has a Ryzen 7 9800X3D with an RX 9070 XT 16GB, and the other has a Ryzen 7 5700G with its Vega 8 iGPU. 4K video in VacuumTube worked fine the day before the update. (4k playback for 9070, 1080 playback for vega8)

After the update I had to set the display to 1080p, and with Gamescope upscaling to a 4K display, the performance overlay showed about 75% GPU usage, roughly 1600MHz core clock, and about 43W during video playback with FSR and Sharp active. Changing the scaling filter lowered it to about 36% usage, around 900MHz, and roughly 20W.

Setting the display back to 4K, VacuumTube video ran at about 7fps with roughly 90% GPU usage on my first test. Later tests showed about 24fps, which is why I lowered the resolution to 1080p. Firefox also failed to load video, and the system drew about 30W while it tried. Because both machines behave similarly, I suspect a change in the graphics driver stack or Gamescope instead of a hardware problem.

Idle baseline (no video playing, RX 9070 XT machine): The performance overlay in Game Mode shows about 15% GPU usage, roughly 715MHz core clock, 26°C, and about 30W power draw, with VRAM at about 1.4GB and the memory clock at about 772MHz. CPU usage is about 16%, and Gamescope reports a steady 60fps. A card at this load and clock should draw far less than 30W.

(Edit: I get similar results in other Flatpaks)

Steps for reproducing this issue:

1.	Update a desktop SteamOS install with an AMD GPU to the newest release (3.8.28).
2.	Set the display to 4K and open a 4K video in VacuumTube in Game Mode.
3.	Watch the performance overlay at level 4. GPU usage runs very high, framerate drops to single digits, and power draw stays around 30W or higher.

Screenshot attached: first one is idle, second video playback at 1080p and third is video playback at 4k:

Image Image Image
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