Intel i915GM (xf86-video-intel modesetting) Tearing during playback with XV

Keith Packard keithp at
Thu Feb 22 11:07:44 PST 2007

On Thu, 2007-02-22 at 07:56 +0100, Michel Dänzer wrote:

> I wonder if the support I added to the DRM recently for scheduling DRI
> buffer swaps couldn't be used for this. Things might be more complicated
> with a compositing manager though. Do we know whether the tearing is due
> to the colourspace conversion blit or the compositing manager's reaction
> to the damage event, or possibly even both?

Tearing can only occur when the copy to screen is interrupted by the
retrace, so in a composited environment, you only get a tear when the
screen is updated, and in a non-composited environment you get a tear
when the color space conversion blt to the screen occurs.

Off the top of my head, we want a way to block requests to a particular
drawable until it would be a 'good time' to update that drawable. For
pixmaps, that would be 'right now' while for windows, that would be 'at

We could expose the blocking ability to clients, and then also make Xv
requests automatically block.

The compositing manager wants to update only at vsync anyway, so it
makes sense to have it block; of course, you want to capture as much
damage as possible to avoid waiting an extra retrace for updated
content, right now that would entail blocking *before* responding to the
damage, which seems like a risky move if the goal is to complete the
update before the retrace line hits the in-progress update.

keith.packard at
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