chundoong-lab-ta/SamsungDS22/submissions/HW5/jongho62.kim/kernel.cl

// super super slow sgemm kernel by heehoon


#define TS 32                        // The square-root of the 2D tile-size (== work-group dims)
#define WPT 8                        // The amount of work-per-thread, i.e. the thread-coarsening factor
#define RTS (TS/WPT)                 // The reduced tile-size in one dimension


__kernel void sgemm(__global float *A, __global float *B, __global float *C, int M, int N, int K) {

/*
  const int row = get_local_id(0); // Local row ID (max: TS)
  const int col = get_local_id(1); // Local col ID (max: TS/WPT == RTS)
  
   const int globalRow = TS*get_group_id(0) + row; // Row ID of C (0..M)
   const int globalCol = TS*get_group_id(1) + col; // Col ID of C (0..N)
    
    // Local memory to fit a tile of TS*TS elements of A and B
    __local float Asub[TS][TS];
    __local float Bsub[TS][TS];
    
    float acc = 0.0f;
    const int numTiles = (K-1) / TS + 1;
    
    for(int t=0; t<numTiles; t++)
    {
    const int t_row = 32*t+row;
    const int t_col = 32*t+col;
    
    if(t_col < K && globalRow < M) Asub[row][col] = A[globalRow * K + t_col];
    else
    Asub[row][col] = 0;
    
    if(t_row < K && globalCol < N ) Bsub[row][col] = B[t_row * N + globalCol];
    else
    Bsub[row][col] = 0;
    
    // Synchronise to make sure the tile is loaded
    barrier(CLK_LOCAL_MEM_FENCE);
        
    for(int k=0; k<32; k++)
    {
      acc += Asub[row][k] * Bsub[k][col];
    }
    
    // Synchronise to make sure the tile is loaded
        barrier(CLK_LOCAL_MEM_FENCE);
     }
     if (globalRow < M && globalCol < N) {    
    C[globalRow*N + globalCol] = acc;
    }
   }
*/

      // Thread identifiers
    const int row = get_local_id(0); // Local row ID (max: TS)
    const int col = get_local_id(1); // Local col ID (max: TS/WPT == RTS)
    const int globalRow = TS*get_group_id(0) + row; // Row ID of C (0..M)
    const int globalCol = TS*get_group_id(1) + col; // Col ID of C (0..N)
 
    // Local memory to fit a tile of TS*TS elements of A and B
    __local float Asub[TS][TS];
    __local float Bsub[TS][TS];
 
    // Initialise the accumulation registers
    float acc[WPT];
    for (int w=0; w<WPT; w++) {
        acc[w] = 0.0f;
    }
    
    // Loop over all tiles
    const int numTiles = (K+ TS -1) / TS;
    for (int t=0; t<numTiles; t++) {
 
        // Load one tile of A and B into local memory
        for (int w=0; w<WPT; w++) {
            const int tiledRow = TS*t + row;
            const int tiledCol = TS*t + col;
            
            if(globalRow + w*RTS >= M || tiledCol >=K)
            {
              Asub[row + w*RTS][col] = 0.0f;
            }
            else
            {
              Asub[row + w*RTS][col] = A[(globalRow + w*RTS)*K + tiledCol];
            }
            
            if(tiledRow + w*RTS >= K || globalCol >= N) 
            {
             Bsub[row + w*RTS][col] = 0.0f;  
            }
            else
            {
              Bsub[row + w*RTS][col] = B[(tiledRow + w*RTS)*N + globalCol];
            }
        }
        
        // Synchronise to make sure the tile is loaded
        barrier(CLK_LOCAL_MEM_FENCE);
 
        // Perform the computation for a single tile
        for (int k=0; k<TS; k++) {
            for (int w=0; w<WPT; w++) {
                acc[w] += Asub[row + w*RTS][k] * Bsub[k][col];
            }
        }
 
        // Synchronise before loading the next tile
        barrier(CLK_LOCAL_MEM_FENCE);
    }
 
    // Store the final results in C
    for (int w=0; w<WPT; w++) {
        if (globalRow + w*RTS >= M || globalCol >= N) continue;
        C[(globalRow + w*RTS)*N + globalCol] = acc[w];
    }
  
}