Different results from run to run

OpenCL
1

Calculations on the GPU and CPU coincide only if one thread processes the entire batch of data.

Working version of the code:

      if (tid == 0)
      {
        pCurrCostMin[pix] = AggrCostBad;
        for (int d = 0; d < dCurCount; ++d)
        {
          ushort Cost = pCurrCosts[d];
          pCurrAggrCosts[d] = Cost;
          pCurrCostMin[pix] = min(Cost, pCurrCostMin[pix]);
        }
      }

Not a working option:

  int threadCount = get_local_size(0);

  if (tid == 0)
    pCurrCostMin[pix] = AggrCostBad;

  int iterCount = (dCurCount + threadCount - 1) / threadCount;

  for (int iIter = 0; iIter < iterCount; iIter++)
  {
    int minIdx = iIter * threadCount;
    int maxIdx = minIdx + threadCount;

    if (maxIdx > dCurCount)
      threadCount = dCurCount - minIdx;

    if (tid < threadCount)
    {
      pCurrAggrCosts[minIdx + tid] = pCurrCosts[minIdx + tid];
    }

    if (tid == 0)
    {
      for (int d = 0; d < threadCount; ++d)
      {
        pCurrCostMin[pix] = min(pCurrCosts[minIdx + d], pCurrCostMin[pix]);
      }
    }
    barrier(CLK_LOCAL_MEM_FENCE);
  }
  barrier(CLK_LOCAL_MEM_FENCE);

Tell me, please, what is my mistake

2

due to branching if else, not all threads reach the barriers, the problem is solved

3

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