Bilateral filter performance issue

Hi, ExpertsI had test Bilateral filter in ipp with ippiFilterBilateralGauss and ippiFilterBilateralGaussFast option. But found the performance of ippiFilterBilateralGaussFast is slower than ippiFilterBilateralGauss.

For 1080p 3 channels image on i7-6700k CPU and the latest version of IPP, ippiFilterBilateralGauss cost 10ms to process 1 frame, but ippiFilterBilateralGaussFast cost  500ms to process 1 frame.

Why ippiFilterBilateralGaussFast is slower than ippiFilterBilateralGauss?

Code is as follows:

status = ippiFilterBilateralBorderGetBufferSize_L(filter, size, radius, dataType, channels, distMethod, &specSize, &tmpBufferSize);
status = ippiFilterBilateralBorderInit_L(filter, size, radius, dataType, channels, distMethod, valSquareSigma, posSquareSigma, pSpec);
status = ippiFilterBilateralBorder_8u_C3R_L((Ipp8u*)pSrc, srcStep, (Ipp8u*)pDst, dstStep, size, border, OWN_GET_BORDER_VALP(8u, 3), pSpec, pTmpBuffer);