Hi
v14 daily again ignores the corona threading settings in preferecnes (was same in eary v13 dailies)
i set it to 18 threads on a 56 core machine, but ipr uses 100%.
the PC is absolute unresposive dur8ing IPR usw
this is on a dual xeon.
i wil have to revert as atm this build is unusable that way, hope for a soon fix
thanks!
I am observing the same behavior here on V13 HF1 and the 05.08 V14 DailyPreview. Could you please compare the graphs showing CPU usage in the Windows Task Manager or some 3rd party app (I used Process Explorer) when running IR in V13 and V14? If you are getting different results, please let us know here.
as said i get very different results, i did chekc in task manager.
i have set ipr to use only 60& of the cores. in v23 this is reflected in the task managers cpu usage.
in v14 i get 100% usage
BTW, why use the 14 Preview, since that build is already out as the final build 13 Hotfix 1? The only published preview for C4D is older than the official release.
Same problem here, I tried different values on - Threads and still getting 100% of usage.
13 HF1
Win 11 - latest
C4d 2025 - latest
IPR will slowdown the system drastic making impossible to use. Therefore, production render will get to 100% of usage but doesn’t effect much on computer responsiveness.
Curious that it slows the machine responsiveness - I can have 0 in the IR thread restriction, it uses 100%, but the PC remains responsive. This is a 9950X on Win 11, C4D 2025, Corona 13 HF 1.
I do notice some interesting things about IR thread restrictions when I set them. First, which CPU is being used seems to keep changing, so the result is if I limit it to 10 threads say, I still see all CPUs in Resource Monitor as being busy, but only about 50 or 60% busy. Presumably it is constantly changing as to which are in use and which are free, which is also suggested by setting it to -31 - this should in theory just leave 1 in use, but instead I see 4 being in “partial use” (attached image). Seems to be acting in two pairs, and in each pair when one has a higher usage, the other has a lower usage.
Been a long time since I looked at these graphs, but this does seem like unusual scheduling 
I could be wrong though, and this could just be what is expected from Win 11 scheduling on modern CPUs, someone will have to comment! And it does seem to me this is more like having 2 or 4 threads in use, not 1.
I tried with various CPUs, with V13 HF1 and the V14 daily and I am getting the expected results. Can you try with a lower number of threads used? For example 50% only.
One thing to note here is that “16 out of 32 threads” here doesn’t mean that you will see only 16 logical CPUs working at 100% in the Windows Task Manager and the other 16 sitting idle. The work will be distributed between them in a more “random” way. But it should be 50% overall.
I did a couple more tests:
1 - Using 25% of the threads (-8) resulted the same 100% utilization on all threads ( some threds a bit reduced but very minimal. )
2 - Using 50% of the threads (-16) here was constant changing between 88% - 100%.
Note:
I did a test scene with just a cube and sky on it and it worked as expected reducing the utilization to 50-65%.
Second test with heavier scene it keeps at 100% no matter how many threads are set.
Did you try with a heavier scene?
Depends on what you mean by heavy, all my testing was done on a “real scene”, as attached.
So I
a) Do not see the machine become unresponsive no matter how many threads are used (including thread limit of 0, which is use all).
b) Do see a reduction in threads / CPU used, though maybe about half what I might have expected (so 80% CPU when I might have expected 50% CPU, 7% CPU when I might have expected 3%).
c) See a slight difference in Max, where it shows 60 to 70% usage when I’d expect 50%, so still not what I’d have imagined, but also still less than C4D does with the same thread restrictions.
Devs are still having a look into things
The issue was reproducible on my device. Configuration: Epyc 9654 96 cores (SMT disabled), DDR5 ECC 4800Mhz 128GB; Software Version: Version 13 (Hotfix 1) Build timestamp - Aug 13 2025 11:14:36 Cinema version 2025.3.2;
During my testing, the viewport frame rate was between 400-500 FPS with rendering disabled, and less than 50 FPS with rendering enabled. There was severe stuttering and frame drops, and I couldn’t even control my mouse. Mouse movement was so difficult to control that it felt like the entire PC was about to crash.
After I clicked “Start Render” and tried to drag the mouse, as you can see, it was extremely difficult to control and very jerky.
yes here too, on a dual yeon 56 cores and a 3970X.
one cant even move the mouse or do anything n the pc.it is even hard to stop the ipr sometimes. so the preview is quite unsuable here for us.
the same error was in an older previoew maybe v12 i think and then solved by Ales.
Also, I discovered an interesting phenomenon: when I selected post in the VFB tab, the entire system would become very slow, but when I selected lightmix, the performance miraculously recovered. XD
Thank you, I have modified the number of threads here and disabled half of the threads during debugging, but the problem still exists. Maybe it is not the problem of this setting.
Hey guys, could you please try the newest Preview? There are some improvements in it which hopefully fix issues such as the ones reported in this thread.
https://forum.corona-renderer.com/ Chaos Corona 14 for Cinema 4D Previews (daily builds) - Changelog #msg236181
