Significant slow down of Intel IPP

Hi Experts:

    I think it should a very tough question here. I list the code below, where chunks=94 and fftLen=8192.

for(Int i=0; i<chunks; i++)
{ ......
ippsAdd_32f(data2, data3+i*fftLen, data2, fftLen);
}

This piece of code exists in two projects, but have quite different behavior. In first project, it only cost about 0.2ms, but in second project it cost about 1ms.

I try to changed the code in second project as: 

for(Int i=0; i<chunks; i++)
{ .......
ippsAdd_32f(data2, data3, data2, fftLen);
}

Then the time elapsed of the second project changed from 1ms to 0.2ms.

I can understand moving the data needs time. But I feel confused that why in first project everthing is fine?

I appreciate your expert view on that.

Best Regards,

Sun Cao