[Mesa-dev] [PATCH 3/3] dri3: Add a synchronisation point for texture-from-pixmap

[Chris Wilson]

On Wed, Nov 02, 2016 at 10:09:26AM +0900, Michel Dänzer wrote:
> On 22/10/16 07:00 PM, Chris Wilson wrote:
> > This applies a synchronisation point to GetBuffers() such that binding a
> > texture-from-pixmap its rendering is serialised with X. This matches the
> > synchronisation point inside DRI2, but it is also arguable that implied
> > sync should be explicitly handled by the client by calling glXWaitX()
> > following the binding of all textures. However, currently glXWaitX()
> > only operates on the bound drawable and does not actually flush all
> > Pixmaps associated with the bound context.
> > 
> > This fixes an issue (output lag) where the compositor calls glXWaitX()
> > prior to acquiring the damage region from X and binding the
> > texture-from-pixmap.
> 
> The X server / driver is responsible for flushing the GPU rendering
> corresponding to damage events before they are sent to clients. The
> modesetting driver is known broken in this regard; are there any other
> setups where this is not happening?

The issue here is that the serialisation is happening outside of damage
event. Rough timeline:

client				X

setup report-on-non-zero damage
				flush + send damage event 
throttle
start preparing frame		more rendering
query damage region
				reply with region (no damage event, no flush)
bind texture_from_pixmap

Here the damage region is not flushed and so the compositor cancels the
dirty region for unflushed pixels.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre