Commit 4e1b470d authored by William Gropp's avatar William Gropp
Browse files

Fix bogus datatype perf test

The test in test/mpi/perf/twovec made invalid assumptions about the
performance of two MPI datatype creation routines.  This is a hard test to
get right, but this version is more likely to avoid falsely signalling
an error.
parent cf551af4
......@@ -9,11 +9,20 @@
#include <math.h>
#include "mpi.h"
/* Make sure datatype creation is independent of data size */
/* Make sure datatype creation is independent of data size
Note, however, that there is no guarantee or expectation
that the time would be constant. In particular, some
optimizations might take more time than others.
The real goal of this is to ensure that the time to create
a datatype doesn't increase strongly with the number of elements
within the datatype, particularly for these datatypes that are
quite simple patterns.
#define SKIP 4
#define NUM_SIZES 16
#define FRACTION 0.2
#define FRACTION 1.0
/* Don't make the number of loops too high; we create so many
* datatypes before trying to free them */
......@@ -23,14 +32,15 @@ int main(int argc, char *argv[])
MPI_Datatype column[LOOPS], xpose[LOOPS];
double t[NUM_SIZES], ttmp, tmin, tmax, tmean, tdiff;
double tMeanLower, tMeanHigher;
int size;
int i, j, isMonotone, errs = 0, nrows, ncols, isvalid;
int i, j, errs = 0, nrows, ncols;
MPI_Init(&argc, &argv);
tmean = 0;
size = 1;
for (i = 0; i < NUM_SIZES + SKIP; i++) {
size = 1;
for (i = -SKIP; i < NUM_SIZES; i++) {
nrows = ncols = size;
ttmp = MPI_Wtime();
......@@ -41,9 +51,15 @@ int main(int argc, char *argv[])
if (i >= SKIP) {
t[i - SKIP] = MPI_Wtime() - ttmp;
tmean += t[i - SKIP];
if (i >= 0) {
t[i] = MPI_Wtime() - ttmp;
if (t[i] < 100 * MPI_Wtick()) {
/* Time is too inaccurate to use. Set to zero.
Consider increasing the LOOPS value to make this
time large enough */
t[i] = 0;
tmean += t[i];
for (j = 0; j < LOOPS; j++) {
......@@ -51,19 +67,37 @@ int main(int argc, char *argv[])
if (i >= SKIP)
if (i >= 0)
size *= 2;
tmean /= NUM_SIZES;
/* Now, analyze the times to see that they are nearly independent
* of size */
for (i = 0; i < NUM_SIZES; i++) {
/* The difference between the value and the mean is more than
* a "FRACTION" of mean. */
if (fabs(t[i] - tmean) > (FRACTION * tmean))
/* Now, analyze the times to see that they do not grow too fast
as a function of size. As that is a vague criteria, we do the
following as a simple test:
Compute the mean of the first half and the second half of the
Compare the two means
If the mean of the second half is more than FRACTION times the
mean of the first half, then the time may be growing too fast.
tMeanLower = tMeanHigher = 0;
for (i=0; i<NUM_SIZES/2; i++)
tMeanLower += t[i];
tMeanLower /= (NUM_SIZES/2);
for (i=NUM_SIZES/2; i<NUM_SIZES; i++)
tMeanHigher += t[i];
tMeanHigher /= (NUM_SIZES - NUM_SIZES/2);
/* A large value (even 1 or greater) is a good choice for
FRACTION here - the goal is to detect significant growth in
execution time as the size increases, and there is no MPI
standard requirement here to meet.
If the times were too small, then the test also passes - the
goal is to find implementation problems that lead to excessive
time in these routines.
if (tMeanLower > 0 && tMeanHigher > (1 + FRACTION) * tMeanLower) errs++;
if (errs) {
fprintf(stderr, "too much difference in performance: ");
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