Correct setting for an 8 Core system

[FoldMeBackwards]

Hi,

I'm still a beginner, so I hope this is the right forum and has not been answered anywhere before.

I'm running an 8 Core i7-9700K. Recently I found the following line in the logs:

Reducing thread count from 7 to 6 to avoid domain decomposition by a prime number > 3

Which surprised me a bit, as I was expecting 8 threads. So I manually adjusted the CPU slot to use 8 threads. Which made the message disappear.
I'm not seeing any performance increase/decreases in any of the configurations.

Can anyone shed some light into this or point me to a documentation ? I'm not understanding this correctly.
Shall I leave this to -1 ?

[Neil-B]

-1 is a default setting to allow one core to be reserved to support GPU folding slot … If you are not GPU folding then the change to all 8 is what I would do … but it won't take effect until the next WU

[FoldMeBackwards]

Thanks so if I'm GPU folding I'm actually only folding with 6 CPU's ? right ?

[Neil-B]

yup - and frees up a spare core for a 2nd GPU

[JimboPalmer]

Welcome to Folding@Home!

Yes there is a 'feature' of the GROMACS science code that hates 'large' primes.
7 is always large, 5 is sometimes large, and 3 is never large. Try to choose a number that is a multiple of 2 and/or 3.
2, 3, 4, 6, 8, 9, 12, 16, 18, 24, 27, etc. are good numbers of CPUs to choose.
5. 10. 15, 20 etc may work most of the time. Other numbers will bite you.

(There is another issue with over 32 threads, but you are safe from that)

[FoldMeBackwards]

Thanks, No, I'm not going for a 2nd GPU

So would it make sense to have 2 slots ? One slot with 4 and one with 3 ?
Or is the -1 the best I can do on a 8 Core System ?

[Neil-B]

A 6 would potentially do more for science and points as returning WUs as quickly as possible is desirable (the next gen of the WU depends on the result from the one finishing) but I have never done the math so could be wrong.

[FoldMeBackwards]

Ok thanks. Will stay on - 1 then