| 9:52:54 AM PDT - Thu, Aug 2nd 2012 |
|
I am running NWChem 6.1 on my personal workstation under Ubuntu 12.04. NWChem was built on my machine with openMPI 1.6 . I have an i7-2600K (4 cores, 8 MB cache) and 16 GB of RAM.
I have noticed that when I set the number of processors to 8 NWChem jobs runs slower than when I set the number of processors to 4. For example for an EOM-CCSDT calculation on a water molecule I get the following:
-np 8 : Wall time = 216 s
-np 4 : Wall time = 156 s
-np 1 : Wall time = 359 s
On the other hand when I parallelize a custom C code for numerical analysis using OpenMP, the wall time is faster when np is set to 8.
Intel claim that multithreading could sometimes lead to a decrease of up to 40% in performance, is this what is happening in this case?
|