Clutter FPS report with hardware video decoding (VAAPI)

[Jonathan Phénix <greaterd gmail com>]

Hi,

I currently attempt to determine if my Clutter application currently
redraws too often, causing excess resource use that could be best used
by other applications on the machine. I use the "--clutter-show-fps"
command line parameter to get the FPS information, I get a count
higher than the monitor vertical refresh rate. For example, the
vertical refresh of the monitor is set to 60Hz while Clutter can go up
to 80 FPS. ClutterTimeline::new-frame gives similar results.

Here's an idea of my current setup:

* Software stack very close to what is proposed at
http://intellinuxgraphics.org/2012.07.html
* CPU/GPU: Intel(R) Core(TM) i3-2105
* OpenGL renderer string: Mesa DRI Intel(R) Sandybridge Desktop
* Running Xorg without a window manager
* The application is full screen (1366x768)
* Clutter 1.10.6
* Clutter-Gst 1.5.6

Additionally, the problem only happen with specific setups, it will
only manifest itself with some monitors and if I use the ClutterMedia
actor created by the clutter-gst library for hardware video decoding.
When I don't get the problem, Clutter is capped at 60 FPS which is the
vertical refresh rate of the monitor. I was also able to workaround
the problem by using
"CLUTTER_PAINT=disable-clipped-redraws:disable-culling" which can
bring other performance problems as well.

Is my application redrawing too often, or is the FPS output generated
by "--clutter-show-fps" misleading/inappropriate for counting actual
FPS when hardware video decoding is being used?

Regards,

- Jonathan Phénix