Runtime Efficiency of colorSpace conversion from BGR

edit

I was profiling cvtColor (opencv 3.2) for runtime efficiency.
For an image of size 960x960, i got following results (in ms), for converting from BGR colorspace

On PC (corei5 2.4 Ghz)

Gray(1.47668)<YUV(2.17967)<HLS(2.78009)<Lab(4.44801)<HSV_Full(5.02791)<Luv(5.27403)<HSV(5.54197)

On Raspi 3

Gray(6.04175)<Lab(13.3423)<YUV(16.6426)<HSV_Full(19.5293)<HSV(21.5772)<HLS(32.6913)<Luv(63.4961)

Two things to know:
1) Why BGR2Luv conversion performace is so much different on PC and Raspi3 ?
2) Can we use LUT to improve the runtime Efficiency for colorSpace conversion ?