Cycles CPU 25% load only during rendering #59874

Closed
opened 2018-12-26 17:57:25 +01:00 by filip zelenka · 11 comments

System Information
Operating system: Windows 10 pro
Graphics card: 1080ti
PC: AMD 2990WX, 4x16GB ram

Blender Version
Broken: 2.8 date: 2018-12-24 14:03
Hash: 6d89337257

the rendering uses 25% CPU load
auto-detect 64threads, or fixed 64, both same issue,
render output image size 19201028, tile size 1616, progresive rendering does not work - shows tile rendering
the problem does not occur in blender 2.79 - the load is close to 100% there.

many thanks,
Filip{F6078572}

**System Information** Operating system: Windows 10 pro Graphics card: 1080ti PC: AMD 2990WX, 4x16GB ram **Blender Version** Broken: 2.8 date: 2018-12-24 14:03 Hash: 6d89337257b6 the rendering uses 25% CPU load auto-detect 64threads, or fixed 64, both same issue, render output image size 1920*1028, tile size 16*16, progresive rendering does not work - shows tile rendering the problem does not occur in blender 2.79 - the load is close to 100% there. many thanks, Filip{[F6078572](https://archive.blender.org/developer/F6078572/Untitled-1.jpg)}
Author

Added subscriber: @filanek

Added subscriber: @filanek

Added subscriber: @JasonClarke

Added subscriber: @JasonClarke
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Added subscriber: @gsrb3d

Added subscriber: @gsrb3d
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https:*www.anandtech.com/show/13124/the-amd-threadripper-2990wx-and-2950x-review/2 says 2 dies have direct access, 2 do not. But all of them have caches (L3 being 8MB per CCX, 2 CCX per die) so while they will get a performance hit with the extra hop, they should not be 100% useless. https:*www.guru3d.com/articles-pages/amd-ryzen-threadripper-2990wx-review,4.html gives less than double time for the double hop case, noticeable but caches could hide part of the issue.

ce927e15e0 has special code for 2990WX and while comments talk about nodes 0 and 2 , function calls only use 0 (!?). Suspicously matches that you see 25% used, with 1 & 3 ignored on purpose, 2 not called.

Maybe reverting that commit and testing could show if that is the culprit, and if running with all cores is worse than with half them. In that respect, you probably can try using OS tools to limit 2.79 to different dies (1 without direct RAM, 2 dies but one with the other without, etc) and compare the effects of RAM hops. The important will be seeing the variation in render times between only 2 dies with direct RAM to also using one or both of the indirect RAM dies.

https:*www.anandtech.com/show/13124/the-amd-threadripper-2990wx-and-2950x-review/2 says 2 dies have direct access, 2 do not. But all of them have caches (L3 being 8MB per CCX, 2 CCX per die) so while they will get a performance hit with the extra hop, they should not be 100% useless. https:*www.guru3d.com/articles-pages/amd-ryzen-threadripper-2990wx-review,4.html gives less than double time for the double hop case, noticeable but caches could hide part of the issue. ce927e15e0 has special code for 2990WX and while comments talk about nodes 0 and 2 , function calls only use 0 (!?). Suspicously matches that you see 25% used, with 1 & 3 ignored on purpose, 2 not called. Maybe reverting that commit and testing could show if that is the culprit, and if running with all cores is worse than with half them. In that respect, you probably can try using OS tools to limit 2.79 to different dies (1 without direct RAM, 2 dies but one with the other without, etc) and compare the effects of RAM hops. The important will be seeing the variation in render times between only 2 dies with direct RAM to also using one or both of the indirect RAM dies.

Added subscribers: @Sergey, @ZedDB

Added subscribers: @Sergey, @ZedDB

@Sergey any input on this?

@Sergey any input on this?

This is expected that only node 0 is used. This is explicitly mentioned in the comment in the code itself. This way job thread is likely to be on a node where .blend file data was read.

The commit referenced here is only affecting render preparation step (when data is being converted from Blender structures to Cycles). Path tracing is not affected by this (well, it is not supposed to anyway). Also, from my tests on Threadripper2 i had all cores occupied.

Does it happen with any file? Can it be seen, with, say, classroom or vector scenes from benchmark bundle?

This is expected that only node 0 is used. This is explicitly mentioned in the comment in the code itself. This way job thread is likely to be on a node where .blend file data was read. The commit referenced here is only affecting render preparation step (when data is being converted from Blender structures to Cycles). Path tracing is not affected by this (well, it is not supposed to anyway). Also, from my tests on Threadripper2 i had all cores occupied. Does it happen with any file? Can it be seen, with, say, classroom or vector scenes from benchmark bundle?
Sergey Sharybin was assigned by Sebastian Parborg 2018-12-27 13:46:58 +01:00
Author

just tested, see the attachment please{F6085707}

just tested, see the attachment please{[F6085707](https://archive.blender.org/developer/F6085707/classroom-25_-cpu-load.jpg)}

This issue was referenced by blender/cycles@e6901aaab0

This issue was referenced by blender/cycles@e6901aaab0a187a50dc5873929c046de72afa892

This issue was referenced by 826d7adde7

This issue was referenced by 826d7adde79216d271b78059c05abd10b7559899

Changed status from 'Open' to: 'Resolved'

Changed status from 'Open' to: 'Resolved'
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Reference: blender/blender#59874
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