My opencl test does not run much faster than CPU

Question

I am trying to measure the execution time of GPU and compare it with CPU. I wrote a simple_add function to add all elements of a short int vector. The Kernel code is:

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Answer 1

I did some extra tests and realized that the GPU is optimized for floating point operations. I changed the the test code as below:

void kernel simple_add(global const int * A, global const uint * B, global int* C)
    {
        ///------------------------------------------------
        /// Add 16 bits of each
        int AA=A[get_global_id(0)];
        int BB=B[get_global_id(0)];
        float AH=0xFFFF0000 & AA;
        float AL=0x0000FFFF & AA;
        float BH=0xFFFF0000 & BB;
        float BL=0x0000FFFF & BB;
        int CL=(int)(AL*cos(AL)+BL*sin(BL))&0x0000FFFF;
        int CH=(int)(AH*cos(AH)+BH*sin(BL))&0xFFFF0000;
           C[get_global_id(0)]=CH|CL;               
     }

and got the result that I expected (about 10 time faster):

                CPU time:      741046.665  micro-sec
                GPU time:       54618.889  micro-sec
                ----------------------------------------------------
                CPU time:      741788.112  micro-sec
                GPU time:       54875.666  micro-sec
                ----------------------------------------------------
                CPU time:      739975.979  micro-sec
                GPU time:       54560.445  micro-sec
                ----------------------------------------------------
                CPU time:      755848.937  micro-sec
                GPU time:       54582.111  micro-sec
                ----------------------------------------------------
                CPU time:      724100.716  micro-sec
                GPU time:       56893.445  micro-sec
                ----------------------------------------------------
                CPU time:      744476.351  micro-sec
                GPU time:       54596.778  micro-sec
                ----------------------------------------------------
                CPU time:      727787.538  micro-sec
                GPU time:       54602.445  micro-sec
                ----------------------------------------------------
                CPU time:      731132.939  micro-sec
                GPU time:       54710.000  micro-sec
                ----------------------------------------------------
                CPU time:      727899.150  micro-sec
                GPU time:       54583.444  micro-sec
                ----------------------------------------------------
                CPU time:      727089.880  micro-sec
                GPU time:       54594.778  micro-sec
                ----------------------------------------------------

for a bit heavier floating point operations like below:

        void kernel simple_add(global const int * A, global const uint * B, global int* C)
            {
                ///------------------------------------------------
                /// Add 16 bits of each
                int AA=A[get_global_id(0)];
                int BB=B[get_global_id(0)];
                float AH=0xFFFF0000 & AA;
                float AL=0x0000FFFF & AA;
                float BH=0xFFFF0000 & BB;
                float BL=0x0000FFFF & BB;
                int CL=(int)(AL*(cos(AL)+sin(2*AL)+cos(3*AL)+sin(4*AL)+cos(5*AL)+sin(6*AL))+
                        BL*(cos(BL)+sin(2*BL)+cos(3*BL)+sin(4*BL)+cos(5*BL)+sin(6*BL)))&0x0000FFFF;
                int CH=(int)(AH*(cos(AH)+sin(2*AH)+cos(3*AH)+sin(4*AH)+cos(5*AH)+sin(6*AH))+
                        BH*(cos(BH)+sin(2*BH)+cos(3*BH)+sin(4*BH)+cos(5*BH)+sin(6*BH)))&0xFFFF0000;
                        C[get_global_id(0)]=CH|CL;

             }

The result was more or less the same:

                CPU time:     3905725.933  micro-sec
                GPU time:      354543.111  micro-sec
                -----------------------------------------
                CPU time:     3698211.308  micro-sec
                GPU time:      354850.333  micro-sec
                -----------------------------------------
                CPU time:     3696179.243  micro-sec
                GPU time:      354302.667  micro-sec
                -----------------------------------------
                CPU time:     3692988.914  micro-sec
                GPU time:      354764.111  micro-sec
                -----------------------------------------
                CPU time:     3699645.146  micro-sec
                GPU time:      354287.666  micro-sec
                -----------------------------------------
                CPU time:     3681591.964  micro-sec
                GPU time:      357071.889  micro-sec
                -----------------------------------------
                CPU time:     3744179.707  micro-sec
                GPU time:      354249.444  micro-sec
                -----------------------------------------
                CPU time:     3704143.214  micro-sec
                GPU time:      354934.111  micro-sec
                -----------------------------------------
                CPU time:     3667518.628  micro-sec
                GPU time:      354809.222  micro-sec
                -----------------------------------------
                CPU time:     3714312.759  micro-sec
                GPU time:      354883.888  micro-sec
                -----------------------------------------