loop unrolling for matrix multiplication

Question

I need to make a good implementation for matrix multiplication better than the naive method here is the methods i used : 1- removed false dependencies which made the performance a lot better 2- used a recursive approach and then there is something i need to try loop unrolling. The thing is each time i used it , it makes the performance worst i can't find an explanation for it i need help here is the code

 for (i = 0; i < M; i++)
    for (j = 0; j < N; j++) {
    double sum = 0;
        #pragma unroll(5)
          for (k = 0; k < K; k++)
        {
        sum +=  A[i + k*LDA] * B[k + j*LDB];
        }
        C[i + j*LDC] = sum ;
    }