topic Re: MKL Parallelism problem in Intel® oneAPI Math Kernel Library

MKL Parallelism problem

sspine — Thu, 13 Nov 2008 07:51:10 GMT

I'm trying MKL10 with OpenMP on dual-core linux machine.

The MKL user's guide told me:

In Intel MKL 10.0, the OpenMP* software determines the default
number of threads. The default number of threads is equal to the number
of logical processors in your system for Intel OpenMP* libraries.

But this is not the truth for me. I have tried cblas_dgemm function (matrix multiply) using the default settings, MKL only uses one core for the calculation. But after I set the environment variable MKL_NUM_THREADS to 2, the MKL can utilize both cores, and the calculation time is about 1/2 of the first case.

The following are my settings:

MKL: 10.0.4.023 with customized shared library

OS: SuSE Linux 10.2, 32-bit

CPU: Intel Core2 Duo

Can someone tell me what on earth the default behaviour of MKL as for MKL_NUM_THREADS?

Thanks!

Re: MKL Parallelism problem

sspine — Wed, 19 Nov 2008 03:30:53 GMT

No one can answer this question?

MKL user manual tells me that the default value of OMP_NUM_THREADS=2. But the user manul does not tell me the default value of MKL_NUM_THREADS. I guess MKL_NUM_THREADS=1 by default. Since MKL_NUM_THREADS takes precesence over OMP_NUM_THREADS, the multi-core support is disabled by default. If this is the truth, it can be approved by my experiment.

Another question is function set_mkl_num_threads() will depend on what libraries? Linux always tell me that some functions unavailable, but I do not know where can I find them.

Re: MKL Parallelism problem

Vladimir_Lunev — Tue, 02 Dec 2008 16:01:43 GMT

Quoting - sspine

No one can answer this question?

MKL user manual tells me that the default value of OMP_NUM_THREADS=2. But the user manul does not tell me the default value of MKL_NUM_THREADS. I guess MKL_NUM_THREADS=1 by default. Since MKL_NUM_THREADS takes precesence over OMP_NUM_THREADS, the multi-core support is disabled by default. If this is the truth, it can be approved by my experiment.

Another question is function set_mkl_num_threads() will depend on what libraries? Linux always tell me that some functions unavailable, but I do not know where can I find them.

Hi,

MKL uses "Number of physical cores" threads by the default. If you has set MKL_NUM_THREADS or OMP_NUM_THREADS to the positive value then this value is used instead of the default.

Please, how did you link MKL?

Thanks,
-Vladimir