[Bug 296481] [NEW] Video stutter / mouse jumps in Kubuntu Intrepid

[Jakob Petsovits]

Public bug reported:

Binary package hint: kubuntu-desktop

Since I updated to Kubuntu Intrepid (which was about a month before its
release or so), Kubuntu shows a two weird bugs, with a pretty clear sign
that those are related and probably stem from the same issue.

Symptom 1.
Video playback (with all kinds of different players, including Dragon, Kaffeine, VLC and Flash Player videos) stutters every few (5-8?) seconds or so, for a fraction of a second, plays back nicely otherwise. Sound works flawlessly. The issue also occurs when simply running glxgears, and brief testing on the desktop would suggest that this is not a video playback issue at all but that the whole display is on hold for that short time.

The forum thread at http://ubuntuforums.org/showthread.php?t=939027
found out that this does not happen in fluxbox, or in GNOME using
compiz. I can confirm that video playback does not stutter in fluxbox.
It still happens with compiz in a KDE session, and also with KWin trunk.
KWin is therefore innocent. I also noticed Symptom 2 very early in the
session startup, so it's definitely not caused by a normal application
but by some permanent ("startup") kded service or other fundamental
stuff like Plasma.

Furthermore, the reports in that thread indicate that this might be an
issue of the i945 graphics driver, and I've also got that piece of
hardware. Given that I haven't yet found a report of this issue
happening with other graphics cards, this issue should be assumed to be
specific to i945 cards.

Symptom 2.
When I leave the mouse pointer without moving, it jumps about 3-5 pixels to the right. When I move the cursor again, it starts from its original position further left, as if it had never jumped right. Steadily reproducible - I can somehow live with it, but it still gets on my nerves. No mouse events seem to be sent to the system for the mouse cursor jump. (I tried on the Krita canvas which has an associated X/Y pixel position display, and it does not change when the cursor jumps.) The jumps occurs after a similar timespan as the video stutter does (I watched it a few times, it goes around 4-7 seconds).

Now here comes the interesting part.

The thread http://ubuntuforums.org/showthread.php?t=953052 recognizes
that the mouse jump coincides with the video stutters. I can confirm
that too, easily reproducible with glxgears. Furthermore, I just
analyzed the mouse jump times a bit more, and the jump happens all 10
seconds (currently at 8, 18, 28, 38, 48 and 58 seconds in any given
minute, but I believe that depends on when the timer starts). So there
is good reason to believe that a timer triggers every 10 seconds, and
causes the delay by whatever action it executes.

I had been running the same version of KDE 4 on Hardy where both of
these issues did not show up, still they don't manifest outside of a KDE
session. Therefore, it seems probable to me that that some KDE component
interacts with the graphics subsystem (or whatever) in Intrepid, in a
different way than it did in Hardy. That makes the X update and KRandR
service a prime suspect, going to test that sucker right now. Could be
something else, though.

** Affects: kubuntu-meta (Ubuntu)
     Importance: Undecided
         Status: New

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Video stutter / mouse jumps in Kubuntu Intrepid
https://bugs.launchpad.net/bugs/296481
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