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tweak: fix parallelism in squiggle.c

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NunoSempere 2023-11-27 14:16:38 +00:00
parent 06e78cb079
commit 825336ef0a
2 changed files with 26 additions and 7 deletions
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squiggle.c/samples
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squiggle.c/squiggle_c/squiggle_more.c
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@ -306,10 +306,25 @@ ci convert_lognormal_params_to_ci(lognormal_params y)
/* Parallel sampler */ /* Parallel sampler */
void parallel_sampler(double (*sampler)(uint64_t* seed), double* results, int n_threads, int n_samples){ void parallel_sampler(double (*sampler)(uint64_t* seed), double* results, int n_threads, int n_samples){
if((n_samples % n_threads) != 0){
fprintf(stderr, "Number of samples isn't divisible by number of threads, aborting\n"); // Division terminology:
exit(1); // a = b * quotient + reminder
} // a = (a/b)*b + (a%b)
// dividend: a
// divisor: b
// quotient = a / b
// reminder = a % b
// "divisor's multiple" := (a/b)*b
// now, we have n_samples and n_threads
// to make our life easy, each thread will have a number of samples of: a/b (quotient)
// and we'll compute the remainder of samples separately
// to possibly do by Jorge: improve so that the remainder is included in the threads
int quotient = n_samples / n_threads;
int remainder = n_samples % n_threads;
int divisor_multiple = quotient * n_threads;
uint64_t** seeds = malloc(n_threads * sizeof(uint64_t*)); uint64_t** seeds = malloc(n_threads * sizeof(uint64_t*));
for (uint64_t i = 0; i < n_threads; i++) { for (uint64_t i = 0; i < n_threads; i++) {
seeds[i] = malloc(sizeof(uint64_t)); seeds[i] = malloc(sizeof(uint64_t));
@ -321,14 +336,18 @@ void parallel_sampler(double (*sampler)(uint64_t* seed), double* results, int n_
{ {
#pragma omp for #pragma omp for
for (i = 0; i < n_threads; i++) { for (i = 0; i < n_threads; i++) {
int lower_bound = i * (n_samples / n_threads); int lower_bound_inclusive = i * quotient;
int upper_bound = ((i+1) * (n_samples / n_threads)) - 1; int upper_bound_not_inclusive = ((i+1) * quotient); // note the < in the for loop below,
// printf("Lower bound: %d, upper bound: %d\n", lower_bound, upper_bound); // printf("Lower bound: %d, upper bound: %d\n", lower_bound, upper_bound);
for (int j = lower_bound; j < upper_bound; j++) { for (int j = lower_bound_inclusive; j < upper_bound_not_inclusive; j++) {
results[j] = sampler(seeds[i]); results[j] = sampler(seeds[i]);
} }
} }
} }
for(int j=divisor_multiple; j<n_samples; j++){
results[j] = sampler(seeds[0]);
// we can just reuse a seed, this isn't problematic because we are not doing multithreading
}
for (uint64_t i = 0; i < n_threads; i++) { for (uint64_t i = 0; i < n_threads; i++) {
free(seeds[i]); free(seeds[i]);