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cmpi
Noro96
Noro96

Reputation: 113

MPI Gatherv not working (message truncated)

Hello I have a problem with MPI_Gatherv, which is not able to 'gather' values, because it returns:

Fatal error in MPI_Gatherv: Message truncated, error stack: MPI_Gatherv failed(sbuf=0x000001E0AAE36920, scount=16, MPI_INT, rbuf=0x000001E0AAE367E0, rcnts=0x000001E0AAE18500, displs=0x0000005A09F6F9D8, MPI_INT, root=0, MPI_COMM_WORLD) failed Message truncated; 16 bytes received but buffer size is 16

Code is in language C. my code:

#include "stdio.h"
#include "mpi.h"
#include <stdlib.h>

int* multiply(int* x, int xLength, int* y, int yLength) {

    int* resultMatrix = (int *) malloc(xLength*yLength * sizeof(int));
    int r = 0;

    for (int i = 0; i < xLength; i++) {
        for (int j = 0; j < yLength; j++) {
            resultMatrix[r] = x[i] * y[j];
            printf("\nresult[%d]: %d", r, resultMatrix[r]);
            r++;
        }
    }
    return resultMatrix;
}

int* countOfValuesOfProcess(int matrixLength, int numOfProcesses) {
    int* countOfValuesOfProcess = (int*) malloc (numOfProcesses);
    for (int i = 0; i < numOfProcesses; i++) {
        if (i == numOfProcesses - 1) {
        countOfValuesOfProcess[i] = (matrixLength / numOfProcesses) + (matrixLength % numOfProcesses);
        }else countOfValuesOfProcess[i] = matrixLength / numOfProcesses;
    }
    return countOfValuesOfProcess;
}

int main(argc, argv)
int argc; char *argv[];
{
    int x[] = { 1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16};
    int y[] = { 2,3, -1, 4 };
    int* result;
    int size, rank;
    int* recieveInt;
    MPI_Status status;
    MPI_Init(NULL, NULL);
    MPI_Comm_size(MPI_COMM_WORLD, &size);
    int xSize = sizeof(x) / sizeof(x[0]);
    int ySize = sizeof(y) / sizeof(y[0]);


    result = (int *) malloc((xSize * ySize) * sizeof(int));

    MPI_Comm_rank(MPI_COMM_WORLD, &rank);
    int* numOfValuesPerProcess = countOfValuesOfProcess(xSize, size);
    int displs[4];

    recieveInt = (int *) malloc(numOfValuesPerProcess[rank] * sizeof(int));

int* resultPart = (int *) malloc((numOfValuesPerProcess[rank] * ySize) * sizeof(int));

//displs count
if (rank == 0) {
        displs[0] = 0;
        for (int i = 1; i < size; i++) {
            displs[i] = (displs[i - 1] + numOfValuesPerProcess[i - 1]);
        } 
    }

    MPI_Scatterv(x, numOfValuesPerProcess, displs, MPI_INT, recieveInt, numOfValuesPerProcess[rank], MPI_INT, 0, MPI_COMM_WORLD);

    resultPart = multiply(recieveInt, numOfValuesPerProcess[rank], y, ySize);

    MPI_Gatherv(resultPart, numOfValuesPerProcess[rank]*ySize, MPI_INT, result, numOfValuesPerProcess, displs, MPI_INT, 0, MPI_COMM_WORLD);

        free(resultPart);
        free(recieveInt);
    }
    MPI_Finalize();
    return(0);
}

When I replace in gatherv part: numOfValuesPerProcess[rank]*ySize to only numOfValuesPerProcess[rank] it will work but the result will be:

gathered matrix[0]: 2
gathered matrix[1]: 3
gathered matrix[2]: -1
gathered matrix[3]: 4
gathered matrix[4]: 10
gathered matrix[5]: 15
gathered matrix[6]: -5
gathered matrix[7]: 20
gathered matrix[8]: 18
gathered matrix[9]: 27
gathered matrix[10]: -9
gathered matrix[11]: 36
gathered matrix[12]: 26
gathered matrix[13]: 39
gathered matrix[14]: -13
gathered matrix[15]: 52
gathered matrix[16]: -842150451
gathered matrix[17]: -842150451
gathered matrix[18]: -842150451
gathered matrix[19]: -842150451
gathered matrix[20]: -842150451
gathered matrix[21]: -842150451
gathered matrix[22]: -842150451
gathered matrix[23]: -842150451
gathered matrix[24]: -842150451
gathered matrix[25]: -842150451
gathered matrix[26]: -842150451
gathered matrix[27]: -842150451
gathered matrix[28]: -842150451
gathered matrix[29]: -842150451
gathered matrix[30]: -842150451
gathered matrix[31]: -842150451
gathered matrix[32]: -842150451
gathered matrix[33]: -842150451
gathered matrix[34]: -842150451
gathered matrix[35]: -842150451
gathered matrix[36]: -842150451
gathered matrix[37]: -842150451
gathered matrix[38]: -842150451
gathered matrix[39]: -842150451
gathered matrix[40]: -842150451
gathered matrix[41]: -842150451
gathered matrix[42]: -842150451
gathered matrix[43]: -842150451
gathered matrix[44]: -842150451
gathered matrix[45]: -842150451
gathered matrix[46]: -842150451
gathered matrix[47]: -842150451
gathered matrix[48]: -842150451
gathered matrix[49]: -842150451
gathered matrix[50]: -842150451
gathered matrix[51]: -842150451
gathered matrix[52]: -842150451
gathered matrix[53]: -842150451
gathered matrix[54]: -842150451
gathered matrix[55]: -842150451
gathered matrix[56]: -842150451
gathered matrix[57]: -842150451
gathered matrix[58]: -842150451
gathered matrix[59]: -842150451
gathered matrix[60]: -842150451
gathered matrix[61]: -842150451
gathered matrix[62]: -842150451
gathered matrix[63]: -842150451

As we can see the first 16 numbers are gathered but the rest is missing (because we wanted only part of full result) I don't know where is problem I tried to set bigger memory allocation for variable int* result, but not worked.

Where could be a problem ? Thanks for all advices

Upvotes: 0

Views: 2291

Answers (1)

Savithru
Savithru

Reputation: 755

In your MPI_Gatherv call, you send numOfValuesPerProcess[rank]*ySize elements from each rank, but only reserve space for numOfValuesPerProcess[rank] elements on the receiving side. After you do the multiplication, you are sending/receiving ySize times more data, so the recvcounts and displs arguments for the MPI_Gatherv call need to account for that ySize factor.

As an aside, you also seem to have many memory leaks, with not enough frees for the number of mallocs. Learn to use a tool like valgrind to help find and fix these.

Updated code:

#include "stdio.h"
#include "mpi.h"
#include <stdlib.h>

int* multiply(int* x, int xLength, int* y, int yLength) {

    int* resultMatrix = malloc(xLength*yLength * sizeof(int));
    int r = 0;

    for (int i = 0; i < xLength; i++) {
        for (int j = 0; j < yLength; j++) {
            resultMatrix[r] = x[i] * y[j];
            //printf("\nresult[%d]: %d", r, resultMatrix[r]);
            r++;
        }
    }
    return resultMatrix;
}

int* countOfValuesOfProcess(int matrixLength, int numOfProcesses) {
    int* countOfValuesOfProcess = malloc(numOfProcesses * sizeof(int));
    for (int i = 0; i < numOfProcesses; i++) 
    {
        if (i == numOfProcesses - 1) {
        countOfValuesOfProcess[i] = (matrixLength / numOfProcesses) + (matrixLength % numOfProcesses);
        }
        else
        {
         countOfValuesOfProcess[i] = matrixLength / numOfProcesses;
        }
    }
    return countOfValuesOfProcess;
}

int main(int argc, char *argv[])
{
    int x[] = { 1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16};
    int y[] = { 2, 3, -1, 4 };
    int* result;
    int size, rank;
    int* recieveInt;
    MPI_Status status;
    MPI_Init(NULL, NULL);
    MPI_Comm_size(MPI_COMM_WORLD, &size);
    int xSize = sizeof(x) / sizeof(x[0]);
    int ySize = sizeof(y) / sizeof(y[0]);

    MPI_Comm_rank(MPI_COMM_WORLD, &rank);
    int* numOfValuesPerProcess = countOfValuesOfProcess(xSize, size);

    int displs[size];
    //displs count
    if (rank == 0) {
      displs[0] = 0;
      for (int i = 1; i < size; i++) {
        displs[i] = (displs[i - 1] + numOfValuesPerProcess[i - 1]);
      } 
    }

    recieveInt = malloc(numOfValuesPerProcess[rank] * sizeof(int));

    MPI_Scatterv(x, numOfValuesPerProcess, displs, MPI_INT, recieveInt, numOfValuesPerProcess[rank], MPI_INT, 0, MPI_COMM_WORLD);

    int* resultPart = multiply(recieveInt, numOfValuesPerProcess[rank], y, ySize);

    for (int i = 0; i < size; i++)
    {
      numOfValuesPerProcess[i] *= ySize;
      displs[i] *= ySize;
    }

    result = (int *) malloc((xSize * ySize) * sizeof(int));
    MPI_Gatherv(resultPart, numOfValuesPerProcess[rank], MPI_INT, result, numOfValuesPerProcess, displs, MPI_INT, 0, MPI_COMM_WORLD);

    if (rank == 0)
    {
      for (int i = 0; i < xSize*ySize; i++)
        printf("result[%d]: %d\n", i, result[i]);
    }

    free(resultPart);
    free(recieveInt);
    free(numOfValuesPerProcess);
    free(result);

    MPI_Finalize();
    return(0);
}

Upvotes: 1

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