Blender 4.2 Dyntopo sculpt fist stroke performance is very laggy #120593
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Reference: blender/blender#120593
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System Information
Operating system: Windows-10-10.0.22621-SP0 64 Bits
Graphics card: NVIDIA GeForce RTX 3090/PCIe/SSE2 NVIDIA Corporation 4.6.0 NVIDIA 552.12
Blender Version
Broken: version: 4.2.0 Alpha, branch: main, commit date: 2024-04-11 21:26, hash:
52cff75ce080Worked: (4.1)
Short description of error
When sculpting a mesh of 500.000 triangles in Dyntopo, the first stroke of any of the tools is very laggy, then on the second stroke it improves a lot. It was OK in 4.1
Exact steps for others to reproduce the error
In 4.2 is much more laggy than in 4.1 in the first stroke, at least in the file I'm working on.
I can't reproduce it on a default cube, but I can upload my file if needed
Blender 4.2 Dyntopo sculpt performance is much worse than 4.1to Blender 4.2 Dyntopo sculpt fist stroke performance is very laggyI can confirm that 4.2 is much slower than 4.0.
I attach the file I used for testing.
It may be a little difficult to bisect due to another regression in the area.
@HooglyBoogly, does this ring any bells?
Unfortunately nothing is standing out in performance profiles for me, and I'm not really noticing a noticeable performance difference between the first and second brush strokes.
do I upload the file to have a look at it?
I did a bit of timing with
SCOPED_TIMERover the weekend and noticed thatSCULPT_stroke_get_location_exinsidesculpt.ccis where the slowdown is happening; I haven't had the chance to dig much further into it though.I was able to repro even with a simple plane heavily subdivided. With an M1 MBA so is platform independent.
Performed several traces on Blender. The first stroke indeed takes longer (detected as hangs in red in XCode Instruments Profiler -> Time Profile)
The second stroke is a bit faster in this case so is not marked in red. By inspecting the call stack I could not find a standing difference, in fact the heaviest call stack is the same for the first and the second stroke:
Heaviest Call Stack Stroke 1 (Severe Hang)
Heaviest Call Stack Stroke 2
As for which commit may have caused the regression I can't tell exactly since trying to go back that far in time
gives me lots of libraries and dependency errors compiling Blender to effectively triage.
The most recent and significant commit in those files has been this refactor from @HooglyBoogly https://projects.blender.org/blender/blender/commit/488de130b39764b2d8564594fc720aa6159e3f39
If someone can test blender before and after that commit we could confirm or rule it out.
@HooglyBoogly could you double check that commit? maybe is a tiny change that caused the overhead and is buried in that refactor?
We agreed in the module meeting to use the "Normal" priority for this report, since it's just the first stroke with the issue, and because the issue isn't clear in the code, so it may be best handled as part of general optimization development.