[Bug 108917] gamma adjustments cause stuttering with amdgpu.dc=1, especially problematic with RedShift etc.

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=108917

            Bug ID: 108917
           Summary: gamma adjustments cause stuttering with amdgpu.dc=1,
                    especially problematic with RedShift etc.
           Product: DRI
           Version: DRI git
          Hardware: x86-64 (AMD64)
                OS: Linux (All)
            Status: NEW
          Severity: normal
          Priority: medium
         Component: DRM/AMDgpu
          Assignee: dri-devel at lists.freedesktop.org
          Reporter: tempel.julian at gmail.com

Created attachment 142685
  --> https://bugs.freedesktop.org/attachment.cgi?id=142685&action=edit
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

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