Hi,
Some more results from my investigations:
Back in February, the MergeGeometryVisitor was changed to be applied on
Group instead of Geode by Jannik Heller (in CC). This has resulted in
substantially longer optimization time of my loaded OpenFlight files
with a large number of polygons. I assume it's a general performance
problem with many geodes/geometries.
The removeChild call from MergeGeometryVisitor ::mergeGroup is the main
culprit and takes about 87% of the time:
group.removeChild(*ditr);
Does Robert or Jannik have any idea about this? I don't feel comfortable
enough with the code to make any changes, but this prevents me from
upgrading my software to the latest OSG version, while I can't go back
either since I need other fixes in 3.5.8. So I'm a bit stuck and would
appreciate any help!
Regards,
Andreas
On 2017-11-19 17:13, Andreas Ekstrand wrote:
Hi Robert,
Yes, the model is ineffective in the sense that it has 150 000
separate triangles on the same level in the scene graph, that's the
nature of basic usage of OpenFlight and I guess that's why the plugin
applies an optimization of its own. But this could be optimized and
merged much faster before and I'm just looking for a way to get it to
behave like that again, to keep my software from being slower in a new
version.
Some results from VTune, where I have manually filtered and presented
the top two culprits in 3.5.1 compared to 3.5.8 (where I gave up after
2 minutes):
3.5.8: TOTAL: 121.4s
* Registry::read -> Optimizer::optimize ->
MergeGeometryVisitor::mergeGroup -> Group::removeChildren ->
OpenThreads::Atomic::operator++ (78.5s)
* Registry::read -> Optimizer::optimize ->
MergeGeometryVisitor::mergeGroup -> Group::removeChildren ->
OpenThreads::Atomic::operator-- (27.4s)
3.5.1: TOTAL: 12.7s
* Registry::read -> Optimizer::optimize ->
Optimizer::StateVisitor::optimize -> Node::setStateSet ->
StateSet::~StateSet -> StateSet::clear ->
StateAttribute::removeParent (2.4s)
* Registry::read -> Optimizer::optimize ->
Optimizer::MergeGeodesVisitor::mergeGeodes -> Node::~Node ->
Node::setStateSet -> StateAttribute::removeParent (2.2s)
The MergeGeometryVisitor was applied in 3.5.1 as well but didn't take
more than about 0.06s. I guess the 3.5.1 results are generally less
interesting but at least they show that MergeGeometryVisitor was not a
problem there.
I don't know if this gives you some ideas directly or if we need to
keep digging. I will have another look shortly either way, but of
course hoping for you or someone else to come up with some bright
ideas to shorten the time to fixing this problem.
Regards,
Andreas
On 2017-11-19 16:28, Robert Osfield wrote:
HI Andreas,
I haven't had a chance to dig further.
One curious thing I noticed is that when I enabled verbose debug
output there was lots of buffer objects being created and destroyed
during the optimisation step. osg::Drawable now assigns
VetextArrayState and VBO's by default for osg::Geometry - this is
required to make VAO support possible. The large number of these
operations suggest lots of creation and merging of osg::Geometry for
this dataset. There is chance tthat this change alone may be causing
a performance slow down.
However, I don't think creation/deletion of osg::Geometry is the crux
of the problem, and may not even be the optimization step - it could
well be down to the nature of the scene graph being created by the
OpenFlight plugin for this dataset. I suspect the source data is
stored in a way that is really inefficient to handle for real-time.
It might be that the OpenFlight plugin just isn't handling the data
well.
As a general rule, running the Optimizer is a last resort for fixing
really bad datasets, ideally datasets should be created in a form that
is appropriate for decent performance right from the start.
Robert.
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