[Bug 97139] [IVB][REGRESSION] i915: Intermittent short system stutter / lag affecting graphics output; bisected to commit f8d03ea

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=97139

--- Comment #1 from Yorick Peterse <yorickpeterse at gmail.com> ---
I recently got myself a 4K display (Dell 2715Q) and ran into this
problem as well. I never noticed it on my laptop's display (X1 Carbon
3rd generation using a WQHD display). Measuring frame rates using
glxgears would occassionally show a drop from 59.9 frames to around 56
frames per second.

Based on the notes left by the reporter I hacked together the patch
named "drm_msleep_470.patch". This patch basically changes the sleep
time from 10 milliseconds to just 1 millisecond. After compiling the drm
module with this patch and rebooting it appears the problem has been
"solved", though this probably won't work for other setups. I tested
this by again running glxgears for a while and noticed no drops in frame
rate.

The patch is based on Linux 4.7.0, it _may_ work with different versions
but I have not tested this. The patch was generated using "git diff".

Yorick

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