[Bug libgomp/108494] Slow thread creation with nested loops in GFortran

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108494

--- Comment #3 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Yeah, we only cache threads at the outermost parallelism level, for nested
parallelism threads are created and destructed as needed.
I know libomp basically never destroys threads (except for
omp_pause_resource{,_all}?), but am not convinced that is a good idea
resource-wise, while it makes pointless benchmarks faster, whenever some
program uses nested parallelism for a short time say from some library once and
then doesn't need it anymore, it will just waste resources.
Most programs don't use omp_pause_resource{,_all} and especially in libraries
it is pretty impossible because the library doesn't know if some other part of
the program doesn't actually use OpenMP.