Hangouts in ChromeOS pegs the GPU at max frequency

Submitted by Nathan Ciobanu

Assigned to Intel GFX Bugs mailing list

Link to original bug (#110750)

Description

Running Hangouts on ChromeOS pegs the GPU at max frequency while the camera is enabled.

A quicker way to reproduce this issue is to access this URL in the Chrome browser: https://appr.tc/?debug=loopback&vsc=vp8&vrc=vp8

A bisect of the ChromeOS kernel releases has pointed to this patch as the point when this issue started occurring:
"7b92c1bd0540 - drm/i915: Avoid keeping waitboost active for signaling threads" which has been backported to chromeos-4.4 and later kernels.

It is quite evident what the patch and the subsequent work intended to do but a user space client like Hangouts seems to increase power consumption with no benefit from the increased performance - IIUC. The GPU utilization is between 30 to 40% while the frequency is max at 1050MHz (on my i7 KBL-Y Pixelbook).

As an experiment we capped the max GT frequency to 500MHz and saw a drop of about 2W with no hit to performance.

Question is: how can we improve the power consumption given the above patch in the Hangouts case?

Note;
On Ubuntu running Hangouts in the Chrome browser we see more GPU frequency scaling but power consumption is still really high.

Since this is more of a question I haven't included logs yet but let me know if you want to see something and I will upload.