[osg-users] how to interpret values shown by stats handler

[Werner Modenbach]

Hi all,

I'm trying to optimize the display speed of my application by testing
various techniques.

In order to do exact measures I implemented a mechanism where I can
trigger single frame() calls from my keyboard.

Curiously the GPU times shown by the stats handler are always drifting
somehow over significant ranges
before getting stable. Does anybody know if there is some averaging over
a couple of frames or is there any other effect
I don't see at the moment? Or is this a kind of caching effect?

It's difficult to judge the effects of techniques under those
circumstances if I don't have an idea what is causing the drifts.

Thanks for any hints.

- Werner -

[Robert Osfield]

Hi Werner,

The values are averaged as otherwise they'd jump around so much that
they would be un-readable blur.

The exact values are all collated in the the various osg::Stats
objects, so perhaps you can have a look at these.

As a general note, OpenGL timing data is not deterministic, this is
partly down to the OpenGL FIFO blocking at different points in the
frame, or sometimes the OS and the driver interacting in different
ways each frame. This effect gets worse the more overloaded your
system is.

This means you need to take the stats as hint to what is going on, but
it's not hard fast, to really understand you need to be aware of how
various things interact.

Robert.

Robert.
On Tue, 17 Jul 2018 at 10:43, Werner Modenbach

Post by Werner Modenbach
Hi all,
I'm trying to optimize the display speed of my application by testing
various techniques.
In order to do exact measures I implemented a mechanism where I can
trigger single frame() calls from my keyboard.
Curiously the GPU times shown by the stats handler are always drifting
somehow over significant ranges
before getting stable. Does anybody know if there is some averaging over
a couple of frames or is there any other effect
I don't see at the moment? Or is this a kind of caching effect?
It's difficult to judge the effects of techniques under those
circumstances if I don't have an idea what is causing the drifts.
Thanks for any hints.
- Werner -
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http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org

[Werner Modenbach]

OK, thanks Robert.

So I do a couple of frames until values stabilize. The shown average is
what I finally need.

- Werner -

Post by Robert Osfield
Hi Werner,
The values are averaged as otherwise they'd jump around so much that
they would be un-readable blur.
The exact values are all collated in the the various osg::Stats
objects, so perhaps you can have a look at these.
As a general note, OpenGL timing data is not deterministic, this is
partly down to the OpenGL FIFO blocking at different points in the
frame, or sometimes the OS and the driver interacting in different
ways each frame. This effect gets worse the more overloaded your
system is.
This means you need to take the stats as hint to what is going on, but
it's not hard fast, to really understand you need to be aware of how
various things interact.
Robert.
Robert.
On Tue, 17 Jul 2018 at 10:43, Werner Modenbach

Post by Werner Modenbach
Hi all,
I'm trying to optimize the display speed of my application by testing
various techniques.
In order to do exact measures I implemented a mechanism where I can
trigger single frame() calls from my keyboard.
Curiously the GPU times shown by the stats handler are always drifting
somehow over significant ranges
before getting stable. Does anybody know if there is some averaging over
a couple of frames or is there any other effect
I don't see at the moment? Or is this a kind of caching effect?
It's difficult to judge the effects of techniques under those
circumstances if I don't have an idea what is causing the drifts.
Thanks for any hints.
- Werner -
_______________________________________________
osg-users mailing list
http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org

_______________________________________________
osg-users mailing list
http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org