I have identified an issue with jobs that use multiple cpu cores. I do like to use Milkyway@home, using the nbody application which uses multiple cores. I would set in preferences to use 70% of the CPU, and request nbody applications. At 70% of CPU with 12 cores, I would obtain tasks that use 8 cores. I would like to use the the reaming cores on other applications. So I would set Milkyway to no new tasks, reset the CPU preferences back to say 95%. Other apps like world community grid or Rosetta would run in these additional CPU cores - and then stop - go into "waiting to run". If I suspend the milkyway 8 core nbody job, the cores will become active again. When I restart the milkyway nbody task, tasks will continue to run in the remaining available CPU cores - for some period of time. I do have 2 GPU cards. It appears to me that whenever a condition arises that causes BOINC to recalcuate the availabe CPU's, that tasks such as nbody using multicore CPU's will somehow "assume" that they will use 100% of the cores (except for GPU tasks)..

Bottom line, if I set my CPU available to 100% - 12 cores, and have an nbody task running identified at 8 CPU cores, after a short time, only the 8 CPU core nbody task ( and GPU tasks) are running, all other tasks are waiting to run mode.

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Which version of BOINC are you using? There was a change between v7.14 and v7.16 which may address this.

I would extend the amount of work downloaded, and add some projects that use only 1 CPU core.
The benefit is only minor, running 8 core WUs, vs 8 separate threads. Especially if half of the WUs are being processed on another CPU die (dual socket systems, or chipsets like the Ryzen 9 3000 series that have 2 or 4 separate CPUs built under the lid).
Might be better if you could limit the amount of cores per WU to 4. That way there's more flexibility.

I am running version 7.16.5

And new information:

I noticed that boinc CPU execution became "hung". noticecd by viewing task manage, and not seeing any percent increase in task progress. I suspended all tasks, then shut down boinc, restarted, and the tasks that were identified previously as 8 core cpu's including the task in progress, changed to 12 core CPU (as settings were 100% on this 12 core system. I released the in progress task, now labeled as 12 core, and all appears well, running at 95+/-% system capacity essentially using all cores.,

I appear to not have an issue or problem. Very interesting to see that multi core tasks - at least nbody tasks - can have their multi cores usage adjusted during the boinc start process.

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