How to determine the number of CPUs and amount of RAM should I use in Gaussian ?

Julien

Hi,
Recently, I started to run my first calculations using Gaussian on a workstation : Nb of core : 6, 12 threads, and 64 GB in memory.

Should I use blindly all the the 6 core and the full amount of memory every time i run a calculation in purpose to speed it up, or there is some rules to assign the number of CPUs and amount of memory necessary to fastly terminate a job.
I read in some web page : "The following formula can be used to estimate the memory requirement of various types of Gaussian jobs (in 8-byte words):  M + 2(NB)^2, where NB is the number of basis functions used in the calculation, and M is a minimum value that is usually generously covered by the default memory size."

sobereva

If you are using 32 bit Gaussian, you can at most use four CPU cores. If you are using 64bit Gaussian, you should set %nprocs=6 (number of CPU physical cores) to maximally use CPU resources.

If there is no other applications that take up a lot of memory, it is suggested to set %mem=55GB to maximally and safely use spare physical memory.

Julien

sobereva 发表于 2022-4-9 11:20
If you are using 32 bit Gaussian, you can at most use four CPU cores. If you are using 64bit Gaussia ...

Thank you very much for the clarifications.
I just want to understand two more things:
1-is it possible to use the number of logical cores (in my case : 12 logical core) ?
2-which keyword we use in Gaussian, %NProcShared, or %NProc ?

abin

Either %nproc or %nprocshared does the job.
For gaussian 16, use %cpu instead.
Check the manual for details.

Julien

abin 发表于 2022-4-9 17:52
Either %nproc or %nprocshared does the job.
For gaussian 16, use %cpu instead.
Check the manual f ...

Thank you very much abin,
Is it possible to use the number of logical cores (in my case : 12 logical core) ?

abin

Julien 发表于 2022-4-10 13:38
Thank you very much abin,
Is it possible to use the number of logical cores (in my case : 12 logi ...

g09, negative.
g16, %CPU=0-11/2.

Or, you can disable hyper threads.

snljty

abin 发表于 2022-4-10 14:00
g09, negative.
g16, %CPU=0-11/2.

按照卢老师的测试结果http://sobereva.com/392，这个不是物理核心间隔着使用，每个被用的物理核心两个逻辑核心都占满嘛？

abin

snljty 发表于 2022-4-11 18:29
按照卢老师的测试结果http://sobereva.com/392，这个不是物理核心间隔着使用，每个被用的物理核心两个逻 ...

高斯手册有提及，
仅限于机器所有资源你独占，仅用一半核心最佳。

如果还有别的事情在做，而且有没有资源绑定，当然慢的一塌糊涂了。

我所有的前提都是假定，干活的机器就是干活的，
干活的机器就只用来干活，不会跑什么浏览器呀，文档呀之类的。
而且也是资源独占型的。

当然，对于一边跑计算，还一边跑浏览器，看文献，
是不适用的。

你看我提供的公开的工作站初始配置脚本，
都是默认关闭图形界面的，
都是建议slurm+cgroup 限定的。
另外，在CPU密集型的生产环境，
超线程带来的性能提升有限。
而超线程导致用户的脚本数错资源，
可能造成性能下降，
或者计算等待等，
负面作用一堆……

性能提升有限，麻烦还不止一个的时候，当然是关闭了最佳……


要不，你去租用超算，
开超线程，标价为六分钱，
你喜不喜欢？