I noticed that it appear only on multi-head configuration. Seems like randr is somehow involved in this issue. I switched monitors (left and right) and after I reconfigured X-window environment with xrandr the problem occured again on the right monitor. So the issue concerns right monitor after reconfiguring with randr.

For testing purposes I recompiled older kernel 4.8.0 and there is no such artifacts - everything is working fine. Additionally I have tested the newest kernel 4.13-rc2 - and here still the issue occurs.
So it seems like there is some kind of regression in kernel sources.

Ok, I did bisect on kernel and here below is what I found out. 


[root@localhost linux-git]# git bisect bad
e62929b3f628f4dd023b95bdf63d486d877b8e1e is the first bad commit
commit e62929b3f628f4dd023b95bdf63d486d877b8e1e
Author: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Date:   Tue Nov 8 13:55:33 2016 +0100

    drm/i915/gen9+: Program watermarks as a separate step during evasion, v3.

    The watermark updates for SKL style watermarks are no longer done
    in the plane callbacks, but are now called in a separate watermark
    update function that's called during the same vblank evasion,
    before the plane updates.

    This also gets rid of the global skl_results, which was required for
    keeping track of the current atomic commit.

    Changes since v1:
    - Move line unwrap to correct patch. (Lyude)
    - Make sure we don't regress ILK watermarks. (Matt)
    - Rephrase commit message. (Matt)
    Changes since v2:
    - Fix disable watermark check to use the correct way to determine single
      step watermark support.

    Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
    Reviewed-by: Lyude <cpaul@redhat.com>
    Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
    Link: http://patchwork.freedesktop.org/patch/msgid/1478609742-13603-3-git-send-email-maarten.lankhorst@linux.intel.com
    [mlankhorst: Small whitespace fix in skl_initial_wm]

:040000 040000 4abc0f4fff120402078594f21598019c8d342bbc 4dd296dd5a107668be34da73722d370438638a0a M      drivers




[root@localhost linux-git]# git bisect log
git bisect start '--' 'drivers/gpu/drm/i915'
# bad: [650fc870a2ef35b83397eebd35b8c8df211bff78] Merge tag 'docs-4.13' of git://git.lwn.net/linux
git bisect bad 650fc870a2ef35b83397eebd35b8c8df211bff78
# good: [c8d2bc9bc39ebea8437fd974fdbc21847bb897a3] Linux 4.8
git bisect good c8d2bc9bc39ebea8437fd974fdbc21847bb897a3
# bad: [a318b4c4ea9aa9ad6279286f7989ce4a75d5fd76] drm/i915: Intel panel downclock cleanup
git bisect bad a318b4c4ea9aa9ad6279286f7989ce4a75d5fd76
# good: [c0c8b9ed1b0c14d91ff73624df6d918bb47c8a5e] Merge tag 'drm-for-v4.9' into drm-intel-next-queued
git bisect good c0c8b9ed1b0c14d91ff73624df6d918bb47c8a5e
# good: [bae781b259269590109e8a4a8227331362b88212] drm: Nuke modifier[1-3]
git bisect good bae781b259269590109e8a4a8227331362b88212
# bad: [793b61ea9f9972be0836a9a15d0d6a520daaf124] drm/i915: i915_gem_alloc_context_obj can be static
git bisect bad 793b61ea9f9972be0836a9a15d0d6a520daaf124
# bad: [3975797f3e72bd115c6ba80210c5fe65ebd9e14e] Merge remote-tracking branch 'airlied/drm-next' into drm-intel-next-queued
git bisect bad 3975797f3e72bd115c6ba80210c5fe65ebd9e14e
# good: [2b3c83176e908401f31e26a4c0ba71f6248b11c1] drm/i915: Stop skipping the final clflush back to system pages
git bisect good 2b3c83176e908401f31e26a4c0ba71f6248b11c1
# good: [bb89485e999181a329cafa8e798b6bbf10c1a52a] drm/i915: Create distinct lockclasses for execution vs user timelines
git bisect good bb89485e999181a329cafa8e798b6bbf10c1a52a
# good: [ccf010fb943a649a3ca74bb5cd489a642afaa7ae] drm/i915: Add an atomic evasion step to watermark programming, v4.
git bisect good ccf010fb943a649a3ca74bb5cd489a642afaa7ae
# bad: [27745e829a5cb896249f355f5bdab3249c5455e2] drm/i915/execlists: Use a local lock for dfs_link access
git bisect bad 27745e829a5cb896249f355f5bdab3249c5455e2
# bad: [512b552798bfa3c4e665c34b9618d05c71b753ad] drm/i915/gen9+: Preserve old allocation from crtc_state.
git bisect bad 512b552798bfa3c4e665c34b9618d05c71b753ad
# bad: [e62929b3f628f4dd023b95bdf63d486d877b8e1e] drm/i915/gen9+: Program watermarks as a separate step during evasion, v3.
git bisect bad e62929b3f628f4dd023b95bdf63d486d877b8e1e
# first bad commit: [e62929b3f628f4dd023b95bdf63d486d877b8e1e] drm/i915/gen9+: Program watermarks as a separate step during evasion, v3.



I hope those information will be more helpful.

Is there anything in dmesg?

Created attachment 133065 [details]
dmesg from 4.9.0-rc2 with artifacts

This is the dmesg from first bad commit on 4.9.0-rc2 with artifacts.

Created attachment 133066 [details]
dmesg from 4.13.0-rc2 with artifacts

I attached 2 dmesg files from 2 bad kernels (with artifacts on screen): 
- 4.9.0-rc2
- 4.13.0-rc2

I see nothing wrong in any of those dmesg apart from warning in 4.9.0-rc2.

I forgot to write that those artifacts are quite different on both bad kernels. On 4.9.0-rc2 it looks like one line with artifacts, but on 4.13 it looks like multiple line artifacts - as it can be seen on attached screenshot.

So in other words - there are two artifacts. First one appeared in e62929b3f628f4dd023b95bdf63d486d877b8e1e and it was only one-line artifact (unfortunately no screenshot attached). Then somewhere between 4.9.0-rc2 and 4.13.0-rc2 another one (multi-line) artifacts appeared (in attached screenshot).

Any progress? I've tested newest kernel 4.15.0 and the problem still occurs. And it is even worse - because the artifacts appears on both screens.