ANSYS Fluent number of cores
 

Hello,

I have new PC with 2x Intel Xeon CPU E5-2680 v2 (2,8 GHz) and 64 GB RAM. When I setup all cores for computing (40 cores), the PC computed only with 32 (as I could see it in Task manager). When I tried to use only 32 cores, surprisingly it was faster then with 40 cores.

Does anybody know where is the problem? Is there any limitation in number of cores? Or any special setup?

Thank you in advance!!!

This is a problem of the job scheduler. Since there is only 2x10 physical cores. The best solution is to not use hyperthreading and only run on 20 physical cores. W/ hyperthreading you are at the mercy of the job scheduler.

What does it mean the cpu is only computing with 32 cores? Do you mean that Fluent correctly launches 40 jobs but you only see 32 cores at 100% utilization and the remaining 8 not doing anything (e.g. stuckat 0%)?

Or is it something terrible where you tell Fluent to use launch 40 but it only launches 32?

Thank you very much for your response!

Yes, I meant that Fluent correctly launches 40 cores but only 32 cores work at 100%. The remaining 8 are doing nothing.

It is not terrible :) But strange, and I just wonder why the Fluent does not use every cores. And second strange thing is, that when I setup 32 cores for computing (when Fluent launching), the computation is much more quicker then if Fluent launches 40 cores.

I disabled the hyperthreading, so I used only 20 physical cores and the computing time was the shortest of all my simulations! So I think it is the best solution for me - using only the physical cores.

Thank you again for your help :D

Hello Jiffy

i am now struglling now with the same situation just like you !
because i ve noticed that my laptop I7 (4 cores ) does actually run the same simulation in twice the time of my workstation ( with 24 cores & 48threads ) .

At first i thought it's my licence that cant support the cores but i guess now that with your topic i can understand the problem .

Once You said that you deactivated the hyperthreasing Do you mean disable it from the BIOS or you just entred 20 cores instead of 40 ?

Many Thanks