forked from OSchip/llvm-project
2df65f87c1
It is reported that after enabling hidden helper thread, the program
can hit the assertion `new_gtid < __kmp_threads_capacity` sometimes. The root
cause is explained as follows. Let's say the default `__kmp_threads_capacity` is
`N`. If hidden helper thread is enabled, `__kmp_threads_capacity` will be offset
to `N+8` by default. If the number of threads we need exceeds `N+8`, e.g. via
`num_threads` clause, we need to expand `__kmp_threads`. In
`__kmp_expand_threads`, the expansion starts from `__kmp_threads_capacity`, and
repeatedly doubling it until the new capacity meets the requirement. Let's
assume the new requirement is `Y`. If `Y` happens to meet the constraint
`(N+8)*2^X=Y` where `X` is the number of iterations, the new capacity is not
enough because we have 8 slots for hidden helper threads.
Here is an example.
```
#include <vector>
int main(int argc, char *argv[]) {
constexpr const size_t N = 1344;
std::vector<int> data(N);
#pragma omp parallel for
for (unsigned i = 0; i < N; ++i) {
data[i] = i;
}
#pragma omp parallel for num_threads(N)
for (unsigned i = 0; i < N; ++i) {
data[i] += i;
}
return 0;
}
```
My CPU is 20C40T, then `__kmp_threads_capacity` is 160. After offset,
`__kmp_threads_capacity` becomes 168. `1344 = (160+8)*2^3`, then the assertions
hit.
Reviewed By: protze.joachim
Differential Revision: https://reviews.llvm.org/D98838
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| .. | ||
| hidden_helper_task | ||
| bug_36720.c | ||
| bug_nested_proxy_task.c | ||
| bug_proxy_task_dep_waiting.c | ||
| bug_serial_taskgroup.c | ||
| bug_taskwait_detach.cpp | ||
| kmp_detach_tasks_t1.c | ||
| kmp_detach_tasks_t2.c | ||
| kmp_detach_tasks_t3.c | ||
| kmp_task_modifier_simple_par_new.cpp | ||
| kmp_task_modifier_simple_par_old.cpp | ||
| kmp_task_modifier_simple_ws_new.cpp | ||
| kmp_task_modifier_simple_ws_old.cpp | ||
| kmp_task_reduction_nest.cpp | ||
| kmp_taskloop.c | ||
| kmp_taskloop_5.c | ||
| nested_parallel_tasking.c | ||
| nested_task_creation.c | ||
| omp50_task_depend_mtx.c | ||
| omp50_task_depend_mtx2.c | ||
| omp50_task_depend_mtx3.c | ||
| omp50_taskwait_depend.c | ||
| omp_detach_taskwait.c | ||
| omp_fill_taskqueue.c | ||
| omp_task.c | ||
| omp_task_depend_resize_hashmap.c | ||
| omp_task_final.c | ||
| omp_task_firstprivate.c | ||
| omp_task_if.c | ||
| omp_task_imp_firstprivate.c | ||
| omp_task_priority.c | ||
| omp_task_private.c | ||
| omp_task_red_taskloop.c | ||
| omp_task_shared.c | ||
| omp_taskloop_grainsize.c | ||
| omp_taskloop_num_tasks.c | ||
| omp_taskloop_taskwait.c | ||
| omp_taskwait.c | ||
| omp_taskyield.c | ||
| taskdep_if0.c | ||
| taskdep_if0_2.c | ||