[Development] Scenegraph Triple Buffering

[gunnar.sletta at nokia.com]

QML_RENDERER_TIMING shows you the breakdown of of the renderer per frame. They seem to take about 0-1ms each so your problem is not there.

If you try QML_CANVAS_TIMING instead, you will get the sync (copy of QML state to the scene graph), render and swap times. You could also try to time the time spent in the animationDriver->advance() in the qquickwindowmanager.cpp (which is responsible for executing all the animations and JS bindings attached to it). If neither of these show up as obvious bottlenecks, then I suggest running your app through a profiler :)

cheers,
Gunnar


________________________________
From: ext Dietrich.Gossen at conti-engineering.com [Dietrich.Gossen at conti-engineering.com]
Sent: Tuesday, July 03, 2012 6:12 PM
To: Sletta Gunnar (Nokia-MP/Oslo)
Cc: development at qt-project.org
Subject: Re: [Development] Scenegraph Triple Buffering

Hi,

I set the Samples to 1.
format.setSamples(1);

The rotation looks better now, but still not perfect.
I am not sure how to interpret the output of QML_RENDER_TIMING=1

This is how the output looks like (during rotation):



Do you know any other performance improvements, regarding QML?

Thanks.
Dietrich



Von:        <gunnar.sletta at nokia.com>
An:        <Dietrich.Gossen at conti-engineering.com>
Kopie:        <development at qt-project.org>
Datum:        28.06.2012 13:49
Betreff:        Re: [Development] Scenegraph Triple Buffering
________________________________




On Jun 28, 2012, at 12:57 PM, ext Dietrich.Gossen at conti-engineering.com wrote:

> The used hardware is: i.MX6 Sabrelite (with powerful gpu from vivante)
> Used Qt-Version: 5.0.0 Alpha with eglfs plugin
>
> The Qt Application contains scaling, rotations and moving of images. The application is a comination of QML and C++.
> I am searching for the bottleneck.
>
> The hellogl_es2 example is running with 75 fps (with vsync on). But hellogl_es2 is not using QML.

It also doesn't try to enable multisampling, QQuickView does. Depending on the hardware this can have significant impact on performance. The way to change it right now would be to change the requested format we return in src/quick/scenegraph/qsgcontext.cpp in the function QSGContext::defaultSurfaceFormat().

If you do not want to change the source code, of Qt it is possible to write an adaptation plugin for the scene graph to request (among other things) a different surface format, but to just check the impact, it is not worth it :)

> My first idea was to enable triple buffering, and compare the result to double buffering with vsync.

The threaded renderer, which you should already hit by using the EGLFS plugin, does animations and rendering/swap in different threads, so the overall hit of doublebuffering with a potential wait-for-swap is already greatly reduced as the next frame can be prepared while the render thread is waiting for swap.

You can try the environment variable QML_CANVAS_TIMING=1 which prints out which part of the render loop is taking up time.

cheers,
Gunnar

> Best regards
>
> Dietrich
>
>
>
> Von:        <gunnar.sletta at nokia.com>
> An:        <Dietrich.Gossen at conti-engineering.com>
> Kopie:        <development at qt-project.org>
> Datum:        28.06.2012 11:39
> Betreff:        Re: [Development] Scenegraph Triple Buffering
>
>
>
>
> On Jun 28, 2012, at 10:58 AM, ext Dietrich.Gossen at conti-engineering.com wrote:
>
> > Hi,
> >
> > There is some Qt 5.0 documentation available about QSurfaceFormat::SwapBehavior. There is a constant called QSurfaceFormat::TripleBuffer .
> > Is this feature already implemented and tested in Qt 5 Alpha?
>
> This parameter is picked up by the platform's OpenGL implementation if anything, but none of our desktop backends currently make use of this as the buffering policy is typically decided for us by the system. This is mostly a hint to be picked up by EGL implementations where applicable.
>
> > The reason I am asking, is because we are facing the typical issues with Double buffering and vsync turned on.
> > The fps drops to 30.
>
> What system / setup is this and what are you trying to draw? There is no reason why double buffering combined with vsync should result in 30FPS, unless each frame takes in the range 17-33ms to draw. Does this happen also for a very simple scene?
>
> cheers,
> Gunnar
>
>
> > Thanks
> >
> > Best regards
> >
> > Dietrich Gossen
> > _______________________________________________
> > Development mailing list
> > Development at qt-project.org
> > http://lists.qt-project.org/mailman/listinfo/development
>
>


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