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/*
* Copyright (C) by Argonne National Laboratory
* See COPYRIGHT in top-level directory
*/
#include "mpitest.h"
#include <stdio.h>
#include <stdlib.h>
/* MPI_Allreduce need produce identical results on all ranks. This is
* particular challenging for floating point datatypes since computer
* floating point arithmetic do not follow associative law. This means
* certain algorithms that works for integers need to be excluded for
* floating point.
*
* This test checks when an inapproprate algorithms is used for floating
* point reduction.
*/
/* single-precision float has roughly a precision of 7 decimal digits */
#define BIG 1e6
#define TINY 1e-2
#define N 8
float buf[N];
static void init_buf(int rank, int pos1, int pos2)
{
/* Mix a pair of (BIG, -BIG) and TINY, the sum of array will be the sum of
* all TINYs if we add (BIG, -BIG) first, but different results following
* different associativity. A valid algorithm need to produce consistent
* results on all ranks.
*/
for (int i = 0; i < N; i++) {
if (rank == pos1) {
buf[i] = BIG;
} else if (rank == pos2) {
buf[i] = -BIG;
} else {
buf[i] = TINY;
}
}
}
int main(int argc, char **argv)
{
int errs = 0;
MTest_Init(&argc, &argv);
int rank, size;
MPI_Comm_rank(MPI_COMM_WORLD, &rank);
MPI_Comm_size(MPI_COMM_WORLD, &size);
if (size < 3) {
printf("At least 3 processes required. More (e.g. 10) is recommended.\n");
MPI_Abort(MPI_COMM_WORLD, 1);
}
for (int pos1 = 0; pos1 < size; pos1++) {
for (int pos2 = pos1 + 1; pos2 < size; pos2++) {
init_buf(rank, pos1, pos2);
MPI_Allreduce(MPI_IN_PLACE, buf, N, MPI_FLOAT, MPI_SUM, MPI_COMM_WORLD);
float *check_buf;
if (rank == 0) {
check_buf = malloc(N * size * sizeof(float));
}
MPI_Gather(buf, N, MPI_FLOAT, check_buf, N, MPI_FLOAT, 0, MPI_COMM_WORLD);
if (rank == 0) {
MTestPrintfMsg(1, "BIG positions = (%d, %d), result = [", pos1, pos2);
for (int j = 0; j < N; j++) {
MTestPrintfMsg(1, "%f ", buf[j]);
}
MTestPrintfMsg(1, "]\n");
for (int i = 0; i < size; i++) {
for (int j = 0; j < N; j++) {
if (memcmp(&check_buf[i * N + j], &buf[j], sizeof(float)) != 0) {
if (errs < 10) {
printf("(%d - %d) Result [%d] from rank %d mismatch: %f != %f\n",
pos1, pos2, j, i, check_buf[i * N + j], buf[j]);
}
errs++;
}
}
}
free(check_buf);
}
}
}
MTest_Finalize(errs);
return MTestReturnValue(errs);
}
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