multithreading in IPP?

[grabner]

Hi!

According to

http://software.intel.com/en-us/articles/intel-integrated-performance-primitives-intel-ipp-threading-openmp-faq

and the file "ThreadedFunctionsList.txt" included in IPP-5.3, IPP should support multithreading for the FFT functions on 32bit float arrays. On an Intel Core i7 CPU, I call "ippSetNumThreads(8)", and the function returns successfully (and "ippGetNumThreads" confirms that the number of threads has been set to 8). However, it takes exactly the same time to execute the transform with "ippSetNumThreads(1)" and "ippSetNumThreads(8)", and the Windows task manager constantly displays a CPU usage of 13% (i.e., one core). I tested with different array sizes between 2^8 and 2^24.

Are there additional restrictions for the use of multithreading with IPP, or is it expected to work "out of the box"?

Thanks & kind regards,
Markus

[TimP]

Questions specific to IPP would be more likely to get answers on th IPP forum.
In general, applications which use floating point intensively can't be expected to gain by multiple threads per core.