threads of mkl

[vadim_l]

Hello,
I have a question for the library mkl
I have intel core i3 with 4 logical cores, and was installed Parallel Studio 2011 and the intel composer XE 2011 with version mkl 10.3.1. When I create a project in visual studio I chose the menu option - 'parallel' mkl in composer ,but when the program was started, windows task manager show only 2 working cores, what's the problem?
I tried using the function mkl_set_num_threads(4),but nothing changed.

[barragan_villanueva_]

Hi,

Maybe it's because MKL recognizes HT and limits threads to 1 per core by default to get the best performance.

To allow using all logical cores please set environment MKL_DYNAMIC=false together with settting MKL_NUM_THREADS=4 or using the function mkl_set_num_threads(4).

[vadim_l]

Thanx, Victor,
the function mkl_set_num_threads(4) together with omp_set_dynamic(false) helped me. However, the performance is no much increased.
Tell me please on how many physical cores MKL shows significant performance?

[barragan_villanueva_]

Quoting vadim_l

Tell me please on how many physical cores MKL shows significant performance?

Hi,

In general it depends on MKL domain and tasks you are using. For BLAS for example the best performance will be when used 1-cpu for core (similar toHT is off).
But for other parts you can get some improvements in using HT.