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radeonsi on 7840U Phoenix: high power use when decoding H264 & vp09 with vaapi (software decoding is more efficient)

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The title should effectively distinguish this bug report from others and be specific to issue you encounter. When writing the title of the bug report, include a short description of the issue, the hardware/driver(s) affected and application(s) affected.

System information

Please post inxi -GSC -xx output (fenced with triple backticks) OR fill information below manually

  • OS: (cat /etc/os-release | grep "NAME") Ubuntu 23.10

  • GPU: (lspci -nn | grep VGA or lshw -C display -numeric) AMD Phoenix1 [1002:15bf] (rev dd)

  • Kernel version: (run uname -a) reproducible on ubuntu 6.5, mainline 6.6.2, 6.6.3 and 6.7RC2 and RC3

  • Mesa version: (glxinfo -B | grep "OpenGL version string")

24.0_git2311290600

and also 23.1.1 as shipped in Ubuntu 23.10

  • Desktop manager and compositor: KDE Plasma, kwin in wayland. Also seen on gnome in wayland

Describe the issue

On Ubuntu 6.5 and mainline kernels, and in fact on all kernels I have tried, I observe the following on my Thinkpad P14S AMD7840U. Observations are unchanged after yesterday's 1.16 BIOS update. Results are the same in kde wayland session and gnome wayland session, latest versions of both.

Idle power use in my standard controlled environment wifi on, screen at 30% Power use is measured by battery firmware discharge reporting using the powerstat script on linux, and batteryinfoview logging on Window

This issue is the same even with kernel 6.7RC3 and mesa 24.0+git2311290600 from an Ubuntu PPA (oibaf)

The firmware supports three different power profiles, but it makes no difference for these results in either Windows or Linux.

Idle power (baseline) Linux: 3.4W (best., 3.7 more typical, Windows (3.4W) best, 3.7 more typical

Margin of error in these figures is 0.2W at most, I would say.

Playback of FullHD 30 fps VP09 test video, ten minutes duration.

Power use Windows: 4.4W with hardware decoding active

Cost of video playback with respect to idle is between 0.7W and 1.0W

Linux (all tested kernels)

With hardware decoding on, vaapi via mpv, decoding status confirmed by nvtop and also by changes in power consumption when vaapi decoding in turned on and off during playback via ctrl H.

Vaapi on power use: 7.7W. Cost of decoding about 3.3 W

Vaapi off (CPU usage jumps by about 0.4%): power user 6.4W, cost of decoding 2.3W.

Yes, it uses less power when hardware decoding is off. I can reproduce this result every time.I observe a small but measurable and consistent increase in CPU load when hardware decoding is disabled, but apparently this is a lower power cost than the hardware decoding

Similar results with 30 fps full hd H264 test video (Simpson's movie trailer).

Edited by Tim Richardson
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