topic Multicore performance drop under Windows x64 in Intel® oneAPI Math Kernel Library

Multicore performance drop under Windows x64

lajszlo — Mon, 24 Jan 2011 11:53:58 GMT

I'm using MKL for matrix multiplication (cblas_sgemm function) under 64-bit Windows. This far I'been using 32-bit code, and -- according to the Windows Task Manager -- my routine exploited both my cores to 100%. Now I compiled a 64-bit version from the code, and now Windows Task Manager shows only 50-60% processor use. interestingly, one of the cores is used at about 80%, and the other one about 20% (compared to the earlier 100%-100%). Is there anything I can do to have the same performance with the 64-bit version than with the 32-bit version?
Thanks a lot,

Multicore performance drop under Windows x64

TimP — Mon, 24 Jan 2011 14:25:29 GMT

It looks like you're getting just one thread. This would be expected MKL default behavior if you run on a single core HyperThreaded CPU. In case the OS is confusing MKL into thinking you have a single core when you have dual, does MKL_DYNAMIC help?
Windows 7 is said to have scheduling improvements over earlier versions of Windows X64.

Multicore performance drop under Windows x64

lajszlo — Mon, 24 Jan 2011 15:37:07 GMT

You are right, the 32-bit executable has 3 threads (according to Task Manager), while the 64-bit version has only 1 thread. I forgot to mention that I have Windows XP 64-bit version.
I'm absolutely not familiar with threading in MKL. I added the following two lines to my code:
mkl_set_dynamic(0);
mkl_set_num_threads(2, MKL_BLAS);
but nothing has changed, still there is only one thread. Do you mean this or something else by "does MKL_DYNAMIC help"?
Thanks

Multicore performance drop under Windows x64

Gennady_F_Intel — Tue, 25 Jan 2011 13:10:27 GMT

Which libraries do you use for linking application?

Multicore performance drop under Windows x64

lajszlo — Wed, 26 Jan 2011 08:38:24 GMT

I'm using MKL 10.1.1.022. For the 32-bit version (which works fine) I link mkl_c.lib, mkl_sequential.lib, libiomp5md.lib from the ia32\lib directory. For the x64 version there is no mkl_c.lib in the em64t\lib directory, so I link mkl_core.lib, mkl_intel_lp64.lib, mkl_sequential.lib, libiomp5md.lib. Is that OK? Thanks.

Multicore performance drop under Windows x64

Gennady_F_Intel — Wed, 26 Jan 2011 09:11:17 GMT

No, that not correct. You are using non-threaded libraries. Please try to use,

mkl_intel_lp64.lib mkl_intel_thread.lib mkl_core.liblibiomp5md.lib

as an examplefor static linking with supporting LP64 interface.

For more info, please refer to the Users Guide or see here the Linker Adviser.

Multicore performance drop under Windows x64

lajszlo — Wed, 26 Jan 2011 13:10:42 GMT

This solved the problem, thanks a lot!!