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Maniphest T93861

Mulitiple CPU thread rendering impossible
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Description

System Information
Operating system: Windows 11
Graphics card: RTX 3060 Ti FE
CPU: AMD Ryzen 5 2600 Six Core Processor

Blender Version
Broken: 3.0.0 all releases
Worked: none

Short description of error

CPU render multithreading is not possible.

Exact steps for others to reproduce the error

Activate Cycles render tab, choose CPU for rendering, activate "Use Tiling" under Performance, choose a tiny size e. g. 32 (px). Threads Mode Auto or Fixed acts equal. Press F12 or "Render". Only one thread is rendering. No similar thread is active.

Event Timeline

Bernd Mehrtens (Hero) created this task.Dec 8 2021, 12:55 PM
Bernd Mehrtens (Hero) updated the task description. (Show Details)
Bernd Mehrtens (Hero) updated the task description. (Show Details)Dec 8 2021, 1:03 PM
Effi (BlenderEffi) added a subscriber: Effi (BlenderEffi).Dec 8 2021, 4:18 PM
Thomas Dinges (dingto) added a subscriber: Thomas Dinges (dingto).Dec 8 2021, 4:33 PM

I cannot confirm that issue, it uses 100% CPU here for me. Both with 3.0 and latest master. Windows 10, AMD Ryzen 3700X.

Also note, that the tiling feature has changed. It is now used to save memory on large renders, not for performance tweaking any more. There is no real point setting it so low.

David Black (david_black) added a subscriber: David Black (david_black).Dec 8 2021, 7:25 PM

Hi,

Previously, it was 1 thread per tile. Blender 3.0 uses all threads on the same tile.

Thomas is correct. While testing Cycles X development, tried various tile size render tests. Generally the 2048 setting is optimal, and only needs to be reduced if there's a specific area that's difficult to render, which could slow down the whole render.

Richard Antalik (ISS) changed the task status from Needs Triage to Needs Information from User.Dec 9 2021, 12:38 AM
Richard Antalik (ISS) added a subscriber: Richard Antalik (ISS).

Also can't reproduce here. Can you upload .blend file and send screenshot what CPU utilization looks like in task manager?

Bernd Mehrtens (Hero) added a comment.Dec 9 2021, 8:59 AM

Previously, it was 1 thread per tile. Blender 3.0 uses all threads on the same tile.

This might be the answer, why Blender is rendering only one tile. I was confused, not seeing multiple tiles rendering.

Thomas Dinges (dingto) closed this task as Resolved.Dec 9 2021, 9:27 AM
Thomas Dinges (dingto) claimed this task.

I assume the issue is resolved then, thanks for getting back to us Bernd.