Created attachment 128485 [details]
dmesg output and xorg.0.log
When playing back video files with vlc or mplayer or in browser the playback is not smooth and instead has severe jerkiness. The same issue affects also opengl.
For video playback the issue is 80% reproducible meaning roughly one time out of five video playback will be smooth with mplayer.
This issue has effected this skylake machine for a year with several different kernel, driver and distro versions. In windows or with sandy bridge linux machine playback is smooth.
General performance statistics don't show the effect? E.g. glxgears is steady (that's framerate over 5s so not particular sensitive) Nothing shows up in top/perf for consuming CPU?
glxgears has the jerkiness too with similar reproducibility but it is not good benchmark to look for this issue as the gears move so fast. There are no cpu intensive programs running in the background.
Also, other people seem to have the same issue with skylake linux:
Does it occur also with modesetting driver or Wayland?
Yes, it also occurs with the modesetting Xorg driver.
Created attachment 130065 [details]
Yes, it occurs also with the modesetting driver.
On 03/04/17 20:53, firstname.lastname@example.org wrote:
> *Comment # 4 <https://bugs.freedesktop.org/show_bug.cgi?id=99096#c4>
> on bug 99096 <https://bugs.freedesktop.org/show_bug.cgi?id=99096> from
> email@example.com <mailto:firstname.lastname@example.org> *
> Does it occur also with modesetting driver or Wayland?
> You are receiving this mail because:
> * You reported the bug.
Which video output mplayer is using? Is there difference between -vo xv and -vo gl?
I can see jerkiness with 60 fps video also on sandy bridge with -vo xv. Pause and unpause is fixing it. There are many dropped frames with -vo gl although there is no jerkiness.
Are there dropped frames (is third number from right increasing in mplayer status line)?
What is desktop environment? Some desktop environment like Xfce can run without compositor. Does enabled/disabled compositor make any difference?
The issue occurs with both xv and gl but I use xv by default.
I don't have the issue with a sandy bridge machine at all, only with
skylake. I see the issue in 30fps content too. Pause and unpause does
not fix here. Frame dropping is disabled in mplayer.
This is KDE desktop environment on all test machines, including the
sandy bridge one.
I tried running X directly from console with 'startx' on the problem
skylake machine and now the jerkiness is gone with mplayer. Instead,
sometimes xv playback has constant horizontal tear which goes away with
pause / unpause. With gl there is no tear.
Although there is no major jerkiness anymore without KDE I think
playback is still not quite as smooth as with Windows but it is usable.