Arch Linux

Description:
Since Kernel 4.14 I only get a refresh rate of 40hz on my internel Monitor (eDP-1). Refreshrate is normal on external VGA or HDMI Monitors. I use a Intel HD 4000 Chip.
The Refreshrate is shown as 60 hz in xrandr but is only 40 hz when I test it.
Workaround:
When I manually set the refreshrate to a higher Refreshrate it is show as 70hz,120hz etc. but only is 60 hz.

Here is the output od xrandr with 72hz-Workaround:
Screen 0: minimum 320 x 200, current 1920 x 1080, maximum 8192 x 8192
eDP-1 connected primary 1920x1080+0+0 (normal left inverted right x axis y axis) 344mm x 193mm
1920x1080 60.06 + 40.04
1400x1050 59.98
1280x1024 60.02
1280x960 60.00
1024x768 60.04 60.00
960x720 60.00
928x696 60.05
896x672 60.01
800x600 60.00 60.32 56.25
700x525 59.98
640x512 60.02
640x480 60.00 59.94
512x384 60.00
400x300 60.32 56.34
320x240 60.05
1920x1080_72.00_rb 72.00*
HDMI-1 disconnected (normal left inverted right x axis y axis)
DP-1 disconnected (normal left inverted right x axis y axis)
HDMI-2 disconnected (normal left inverted right x axis y axis)

glxgears show me 60fps on 72 hz and 40fps on 60hz.

The problem only apears with Kernel 4.14 (I also tested newest 4.14.5-1 Kernel). On 4.13 or 4.9 lts its fine.

There are 2 Threads about this Problem in Arch and in the Manjaro Fourum:
https://bbs.archlinux.org/viewtopic.php?id=232354
https://forum.manjaro.org/t/poor-opengl-performance-on-linux-4-14/35453/67