test i there might be some "false sharing" going on with openmp

This commit is contained in:
NunoSempere 2024-01-12 00:11:01 +01:00
parent 95e4532c2c
commit 73ea6f32c2
16 changed files with 14 additions and 7 deletions

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@ -9,6 +9,12 @@
#include <string.h> // memcpy
/* Parallel sampler */
#define CACHE_LINE_SIZE 64
typedef struct padded_seed_t {
uint64_t* seed;
char padding[CACHE_LINE_SIZE - sizeof(uint64_t*)];
} padded_seed;
void sampler_parallel(double (*sampler)(uint64_t* seed), double* results, int n_threads, int n_samples)
{
@ -29,14 +35,15 @@ void sampler_parallel(double (*sampler)(uint64_t* seed), double* results, int n_
int quotient = n_samples / n_threads;
int divisor_multiple = quotient * n_threads;
uint64_t** seeds = malloc((size_t)n_threads * sizeof(uint64_t*));
// uint64_t** seeds = malloc((size_t)n_threads * sizeof(uint64_t*));
padded_seed* seeds = (padded_seed*) malloc(sizeof(padded_seed) * (size_t)n_threads);
srand(1);
for (int i = 0; i < n_threads; i++) {
seeds[i] = malloc(sizeof(uint64_t));
seeds[i].seed = malloc(sizeof(uint64_t*));
// Constraints:
// - xorshift can't start with 0
// - the seeds should be reasonably separated and not correlated
*seeds[i] = (uint64_t)rand() * (UINT64_MAX / RAND_MAX);
*(seeds[i].seed) = (uint64_t)rand() * (UINT64_MAX / RAND_MAX);
// printf("#%ld: %lu\n",i, *seeds[i]);
// Other initializations tried:
@ -53,17 +60,17 @@ void sampler_parallel(double (*sampler)(uint64_t* seed), double* results, int n_
int lower_bound_inclusive = i * quotient;
int upper_bound_not_inclusive = ((i + 1) * quotient); // note the < in the for loop below,
for (int j = lower_bound_inclusive; j < upper_bound_not_inclusive; j++) {
results[j] = sampler(seeds[i]);
results[j] = sampler(seeds[i].seed);
}
}
}
for (int j = divisor_multiple; j < n_samples; j++) {
results[j] = sampler(seeds[0]);
results[j] = sampler(seeds[0].seed);
// we can just reuse a seed, this isn't problematic because we are not doing multithreading
}
for (int i = 0; i < n_threads; i++) {
free(seeds[i]);
free(seeds[i].seed);
}
free(seeds);
}
@ -109,7 +116,7 @@ static double quickselect(int k, double xs[], int n)
double *ys = malloc((size_t)n * sizeof(double));
memcpy(ys, xs, (size_t)n * sizeof(double));
// ^: don't make this operation "destructive"
// ^: don't rearrange item order in the original array
int low = 0;
int high = n - 1;