BMesh data copy with many layers is extremelly slow (100x slower) compared to blender 3.6 #115776

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Mykyta-Petrenko · 2023-12-05T00:53:02+01:00

Mykyta-Petrenko commented

2023-12-05 00:53:02 +01:00

System Information
Operating system: Windows-10-10.0.19045-SP0 64 Bits
Graphics card: Radeon RX 580 Series ATI Technologies Inc. 4.6.0 Core Profile Context 23.11.1.231017

Blender Version
Broken: version: 4.0.1, branch: blender-v4.0-release, commit date: 2023-11-16 16:40, hash: d0dd92834a08
Worked: (newest version of Blender that worked as expected)

Short description of error
Accessing bmesh.verts for meshes with huge amount of shape keys becomes extremelly slow in all blender 4.0 that I have tested.

Exact steps for others to reproduce the error
Here is a simple script to demonstrate the issue

import bpy
import time
import bmesh


# params to get a sphere with the poly count equivalent to high-res character
segments = 256
rign_count = 128
n_keys = 500


def benchmark():
    t1 = time.time()
    # Create a sphere with 
    bpy.ops.mesh.primitive_uv_sphere_add(segments=segments, ring_count=rign_count)

    # Set the created sphere as the active object
    obj = bpy.context.active_object
    
    # Add shape keys to the sphere
    for i in range(n_keys):
        obj.shape_key_add(name=f'Key{i}', from_mix=False)

    # Create a bmesh for the target object
    bm = bmesh.new()
    bm.from_mesh(obj.data)

    t2 = time.time()
    # ISSUE START
    # dummy loop accessing bmesh.verts
    for i, v in enumerate(bm.verts):
        v.co = v.co * 1.0
    # ISSUE END
    
    loop_time = time.time() - t2

    # Write back to the mesh
    bm.to_mesh(obj.data)
    bm.free()

    # Update the mesh
    obj.data.update()
    
    total_time = time.time() - t1
    
    print(f"Total time: {total_time}")
    print(f"Bmesh loop time: {loop_time}")


if __name__ == "__main__":
    benchmark()

**System Information** Operating system: Windows-10-10.0.19045-SP0 64 Bits Graphics card: Radeon RX 580 Series ATI Technologies Inc. 4.6.0 Core Profile Context 23.11.1.231017 **Blender Version** Broken: version: 4.0.1, branch: blender-v4.0-release, commit date: 2023-11-16 16:40, hash: `d0dd92834a08` Worked: (newest version of Blender that worked as expected) **Short description of error** Accessing bmesh.verts for meshes with huge amount of shape keys becomes extremelly slow in all blender 4.0 that I have tested. **Exact steps for others to reproduce the error** Here is a simple script to demonstrate the issue ```Py import bpy import time import bmesh # params to get a sphere with the poly count equivalent to high-res character segments = 256 rign_count = 128 n_keys = 500 def benchmark(): t1 = time.time() # Create a sphere with bpy.ops.mesh.primitive_uv_sphere_add(segments=segments, ring_count=rign_count) # Set the created sphere as the active object obj = bpy.context.active_object # Add shape keys to the sphere for i in range(n_keys): obj.shape_key_add(name=f'Key{i}', from_mix=False) # Create a bmesh for the target object bm = bmesh.new() bm.from_mesh(obj.data) t2 = time.time() # ISSUE START # dummy loop accessing bmesh.verts for i, v in enumerate(bm.verts): v.co = v.co * 1.0 # ISSUE END loop_time = time.time() - t2 # Write back to the mesh bm.to_mesh(obj.data) bm.free() # Update the mesh obj.data.update() total_time = time.time() - t1 print(f"Total time: {total_time}") print(f"Bmesh loop time: {loop_time}") if __name__ == "__main__": benchmark() ```

Mykyta-Petrenko added the

labels 2023-12-05 00:53:03 +01:00

Jesse Yurkovich added

and removed

labels 2023-12-05 01:02:39 +01:00

Jesse Yurkovich commented

2023-12-05 01:03:27 +01:00

Confirmed with a build as far back as August 15th (I have no older builds immediately available). I'll set to high due to the severity of the regression so we can investigate.

Blender 3.6.5
Bmesh loop time: 0.14097070693969727

4.0 Alpha 2023-08-15 5741a5d433
Bmesh loop time: 15.914452314376831

Confirmed with a build as far back as August 15th (I have no older builds immediately available). I'll set to high due to the severity of the regression so we can investigate. Blender 3.6.5 `Bmesh loop time: 0.14097070693969727` 4.0 Alpha 2023-08-15 5741a5d433cd `Bmesh loop time: 15.914452314376831`

👍 1

Jesse Yurkovich added

and removed

labels 2023-12-05 01:03:38 +01:00

Hans Goudey commented

2023-12-05 02:25:20 +01:00

Looks like CustomData_bmesh_copy_data_exclude_by_type has quadratic complexity after 9175d9b7c2.

Looks like `CustomData_bmesh_copy_data_exclude_by_type` has quadratic complexity after 9175d9b7c27b191ea94a41871a7049b068f77bd7.

Hans Goudey commented

2023-12-05 02:31:00 +01:00

Think it's best to first build a struct describing how the layer data should be copied, like MeshToBMeshLayerInfo, then iterate over all the BMesh elements and actually do the copy. That's a significant refactor, but otherwise everything involving CustomData_bmesh_copy_data_exclude_by_type will be slow.

Think it's best to first build a struct describing how the layer data should be copied, like `MeshToBMeshLayerInfo`, then iterate over all the BMesh elements and actually do the copy. That's a significant refactor, but otherwise everything involving `CustomData_bmesh_copy_data_exclude_by_type` will be slow.

Hans Goudey self-assigned this 2023-12-05 15:51:20 +01:00

Hans Goudey changed title from ~~bmesh becomes extremelly slow (x100) compared to blender 3.6~~ to BMesh data copy with many layers is extremelly slow (100x slower) compared to blender 3.6

2023-12-05 17:58:55 +01:00

Hans Goudey referenced this issue from a commit

2023-12-06 04:12:56 +01:00

BMesh: Improve performance when copying attributes in same mesh

Hans Goudey referenced this issue from a commit

2023-12-06 04:12:56 +01:00

BMesh: Use simpler element copy within the same mesh

Hans Goudey referenced a pull request that will close this issue

2023-12-06 04:36:08 +01:00

BMesh: Optimize copying attributes from many elements at once #115824

Hans Goudey referenced this issue from a commit

2023-12-09 05:37:47 +01:00