gamma adjustments cause stuttering with amdgpu.dc=1, especially problematic with RedShift etc.

Submitted by Xul Demonslayer @aufkrawall

Assigned to Default DRI bug account

Link to original bug (#108917)

Description

Created attachment 142685
xorg log

With amdgpu.dc=1, there is stuttering in the moment when gamma adjustments are getting applied. This is not the case with amdgpu.dc=0, it is entirely free of stutter.

Both RedShift and Gnome night light in Xorg session show the very same behavior:
When "nightmode" is getting turned on with a transition effect, there is severe stuttering going on. The same is the case in the opposite direction when turning nightmode off again.

It's also very problematic that the stutter is ongoing, as tools like RedShift in dynamic mode constantly adjust color temperature as the night progresses. There is stutter happening every few seconds because of that.

To reproduce, simply start e.g. RedShift in dynamic mode with "redshift -t 4500:4500 -l 1:1".
The stutter can be easily observed when looking at the animation of www.vsynctester.com in Chromium, which should be absolutely free of stutter without gamma adjustment (perhaps set CPU clock governor to performance). But you should already notice that even moving windows etc. is stuttery, especially during transition effect.

As a workaround, one might want to use "oneshot" mode of RedShift, e.g. "redshift -O 4500". This applies a gamma adjustment just once and thus prevents further stuttering. But that's not how the usage of such tools usually is intended.

linux-drm-next-4.21-wip-6b456d7e60007022d91c701c00c76cdfa8774eaf
xorg-server 1.20.3
gnome 3.30.1
both modesetting and xf86-video-amdgpu-git 18.1.0.20 DDX driver

Attachment 142685, "xorg log":
Xorg.0.log