Previously, this happened when the "node task" first runs, which might
not actually execute the node if there are missing inputs. Deferring the
allocation of storage and default inputs allows for better memory reuse
later (currently the memory is not reused).
This was an oversight in rBdba2d828462ae22de5.
The evaluator uses multiple threads to initialize node states
but it is still in single threaded mode.
`get_main_or_local_allocator` did not return the right allocator
in this case.
The geometry nodes evaluator supports "lazy threading", i.e. it starts out
single-threaded. But when it determines that multi-threading can be
benefitial, it switches to multi-threaded mode.
Now it only creates an enumerable-thread-specific if it is actually using
multiple threads. This results in a 6% speedup in my test file with many
node groups and math nodes.
Lazy-function graphs are now evaluated properly even if they contain
cycles. Note that cycles are only ok if there is no data dependency cycle.
For example, a node might output something that is fed back into itself.
As long as the output can be computed without the input that it feeds into,
everything is ok.
The code that builds the graph is responsible for making sure that there
are no actual data dependencies.
Nodes that were not connected to any output could still impact performance.
While they were never executed, sometimes their inputs could keep references
to geometries that other nodes want to modify. That caused unnecessary geometry
copies, because a geometry can only be modified if it is not shared.
Now, inputs that will never be used are tagged accordingly and they will never
have references to geometries that others might want to modify.
In large node setup the threading overhead was sometimes very significant.
That's especially true when most nodes do very little work.
This commit improves the scheduling by not using multi-threading in many
cases unless it's likely that it will be worth it. For more details see the comments
in `BLI_lazy_threading.hh`.
Differential Revision: https://developer.blender.org/D15976
This refactors the geometry nodes evaluation system. No changes for the
user are expected. At a high level the goals are:
* Support using geometry nodes outside of the geometry nodes modifier.
* Support using the evaluator infrastructure for other purposes like field evaluation.
* Support more nodes, especially when many of them are disabled behind switch nodes.
* Support doing preprocessing on node groups.
For more details see T98492.
There are fairly detailed comments in the code, but here is a high level overview
for how it works now:
* There is a new "lazy-function" system. It is similar in spirit to the multi-function
system but with different goals. Instead of optimizing throughput for highly
parallelizable work, this system is designed to compute only the data that is actually
necessary. What data is necessary can be determined dynamically during evaluation.
Many lazy-functions can be composed in a graph to form a new lazy-function, which can
again be used in a graph etc.
* Each geometry node group is converted into a lazy-function graph prior to evaluation.
To evaluate geometry nodes, one then just has to evaluate that graph. Node groups are
no longer inlined into their parents.
Next steps for the evaluation system is to reduce the use of threads in some situations
to avoid overhead. Many small node groups don't benefit from multi-threading at all.
This is much easier to do now because not everything has to be inlined in one huge
node tree anymore.
Differential Revision: https://developer.blender.org/D15914
