NAMD on Windows 10 with huge performance drop after 39 CPUs

From: Maximilian Ebert (mebert_at_chemcomp.com)
Date: Thu Jun 20 2019 - 02:41:41 CDT

Hi there,

We have a 4 socket Intel Xeon E7-8890 v4 board with a total of 96 true and 192 logical cores. When I start NAMD 2.13 Win64 with 39 cores they are all used to 100%. When I switch to 40 they all idle at around 1-2% and the simulation starts being super slow. Any idea why? Do I need to have some sort of MPI because of the 4 sockets? But even then each socket has 24 true cores and 48 logical. Shouldn’t I be able to max ou the 48 (with hyper threading)? Please see attached two stdout. One for 39 cores the other for 40.

https://drive.google.com/file/d/1-6T4Va70h0sIbeZMycbZZ5MrRyPaeO_E
https://drive.google.com/file/d/1-7jq3_WNW-Ags1LofkWlVgOa509m6Owj

Thanks for any advice.

Best,
Max

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