CODEWITHSUNDEEP
cuda
Emad R
Emad R

Reputation: 21

CUDA is accumulating results from previous run

i am facing weird case that local arrays in the kernel are keeping their values from the previous run, and new values are accumulative results of all runs. i delete the array which were defined dynamically. however the keep accumulating the results. here is an example and code below: the first run results were:

Before: 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 
After: 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 ,

then the next run results were:

Before: 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 
After: 2 , 4 , 6 , 8 , 10 , 12 , 14 , 16 , 18 ,

an so on, the previous run values are not cleared. the question where is glitch? and how can i fix it.

my environment is :

OS: Linux SL7

GPU: Tesla K20m (SM_35)

CUDA version: 8.0

here is my code:

#include <iostream>
#include <numeric>
#include <stdlib.h>
#include <stdio.h>

__global__ void myKernel(int *data, int vectorSize)
{

    int const size = vectorSize;
    int *countArray = new int[size];
    /*Print array values before modifications*/
    printf("\nBefore: ");
    for (int i = 0; i < vectorSize; ++i)
    {
        printf("%d , ", countArray[i]);
    }

    /*Modifying array values*/
    for (int i = 0; i < vectorSize; ++i)
    {
        countArray[i] += data[i];
    }
    printf("\nAfter: ");
    /*Print array values after modifications*/
    for (int i = 0; i < vectorSize; ++i)
    {
         printf("%d , ", countArray[i]);
    }
    printf("\n");
    delete[] countArray;
}
int main(void)
{
     const int size = 9;
     int array[size] ={1, 2, 3, 4, 5, 6, 7, 8, 9};
     int *dev_array;
     cudaMalloc((void**) &dev_array, size * sizeof(int));
     cudaMemcpy(dev_array, array, size * sizeof(int), cudaMemcpyHostToDevice);

     myKernel<<<1, 1>>>(dev_array, size);
     cudaFree(dev_array);
     return 0;
}

Upvotes: 0

Views: 74

Answers (1)

phg1024
phg1024

Reputation: 179

I think you need to explicitly initialize countArray to zeros before using it. Uninitialized array could have any value in it. Just do

  for (int i = 0; i < vectorSize; ++i)
  {
    countArray[i] = 0;
  }

before using countArray.

Upvotes: 3

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