Comment 22 for bug 578342

The test setup I use to quickly reproduce and verify that the problem is there:

1) Play a pure sound which easily revelase playback glitches:
$ gst-launch-0.10 audiotestsrc ! pulsesink

2) Play some video (doesn't matter what) with MPlayer, using plain x11 output and no sound:
$ mplayer /path/to/some/movie.avi -vo x11 -zoom -nosound

3) Test audio starts glitching and the glitching becomes worse if I put the video in fullscreen.

And some observations about test:

1) There is not much load on system during test (MPlayer uses around 40% CPU, Xorg floats under 12% CPU, for a 1024x576 video with no sound).

2) There is a lot less audio glitching if I run things in a completely composited environment (e.g. Compiz with no unredirection for fullscreen windows). If I *do* unredirect fullscreen windows with Compiz the glitching becomes worse in fullscreen.

3) There is alomst no glitching at all if using XV for video playback in the test, instead of plain old x11. Obviously that's not going to help for apps that don't use XV, like fullscreen Flash video streaming or any affected non-video app.

4) The glitching is worse when video window is full screen.

5) HDA intel driver typically always reports that IRQ timing work-around has been activated. This doesn't happen in UMS-mode.

And some observations not just related to the specific test setup:
1) Flash fullscreen video playback causes more severe audio glitches if *not* running composited in fullscreen, for instance under Compiz with "Unredirect fullscreen windows" enabled. This is what typically also takes down wireless (just happened now with current setup, as I was testing Flash and writing this).

2) Flash fullscreen video causes glitches even when redirected in composited env.

3) Flash doesn't use XV, seems to correspond well with MPlayer -vo x11 being much worse than when using -vo xv.

4) There are no playback issues with video during any of these tests, the video is smooth, system not overloaded. And besides, the test sound generator requires almost no resources at all.

5) [ 1535.437114] CE: hpet increased min_delta_ns to 7500 nsec
Don't really know the meaning of this one, but it typically appears during problems with wireless and/or audio when running under KMS. Kernel compensating for what is seen as accuracy issues with system timing ?

6) It doesn't have to be MPlayer-vo-x11 or Flash that triggers problem, I just use them because they so easily reproduce it. I have heard audio popping when scrolling Firefox pages or moving windows around, and I've managed to take down wireless when launching Neverball (OpenGL-game).

7) No matter what IRQ config or snd-hda-intel options I test, the problems are always there with KMS and disappear with UMS.