Accel structs using huge amount of VRAM

[am_wilkins]

Good day,

I'm currently doing some render testing between Arnold CPU and GPU. On this particular scene I'm getting vastly longer render times on the GPU which isn't consistent with other tests I've done.

Checking the logs I noticed that there is a massive amount of VRAM supposedly being used by "accel structs" which I've never seen happen before.

What is "accel structs" and why is the usage so high? (16,297?)

In addition to that, if I manually add the categories together, I would get above the total reported VRAM usuage of 24015.

26,809 + 13,494 (unaccounted) = around 40,303 which is way higher that the 24gb VRAM the RTX 4090 can support.

I know Arnold doesn't support "out of core rendering" yet but this feels like the card is actually ramming out even though the render was success but super slow.

R409| 00:19:41 23849MB         | peak GPU memory consumed 24015.44MB   
R410| 00:19:41 23849MB         |  CUDA context             383.93MB   
R411| 00:19:41 23849MB         |  OptiX context             20.00MB   
R412| 00:19:41 23849MB         |  framebuffers             251.87MB   
R413| 00:19:41 23849MB         |  node overhead             52.25MB   
R414| 00:19:41 23849MB         |  geometry                5707.09MB   
R415| 00:19:41 23849MB         |   polymesh                824.13MB   
R416| 00:19:41 23849MB         |    vertices              1423.75MB   
R417| 00:19:41 23849MB         |    vertex indices        1400.13MB   
R418| 00:19:41 23849MB         |    normals                474.06MB   
R419| 00:19:41 23849MB         |    normal indices         167.65MB   
R420| 00:19:41 23849MB         |    uv coords              246.93MB   
R421| 00:19:41 23849MB         |    uv coords idxs        1276.47MB   
R422| 00:19:41 23849MB         |    P reference (autobump)  276.82MB   
R423| 00:19:41 23849MB         |    N reference (autobump)   92.27MB   
R424| 00:19:41 23849MB         |    uniform indices        349.00MB   
R425| 00:19:41 23849MB         |    other                    0.00MB   
R426| 00:19:41 23849MB         |   subdivs                4882.96MB   
R427| 00:19:41 23849MB         |  accel structs           16297.37MB   
R428| 00:19:41 23849MB         |  skydome importance map     7.80MB   
R429| 00:19:41 23849MB         |  texture cache           4092.87MB   
R430| 00:19:41 23849MB         |  unaccounted             13494.85MB 

all the best,
amwilkins

--

Houdini Core Version 20.5.410
Arnold Core: 7.3.6.0

HotA: 6.3.6.0

CPU: AMD Ryzen TR 3990x / 3970x

RAM: 128GB
GPU: NVIDIA RTX 4090 / RTX A4000
OS: Windows/Linux