I forgot to tell you these code block is inside a parallel OpenMP region. This is the complete code:
#pragma omp parallel num_threads(6)
{
int tid = omp_get_thread_num();
hwloc_obj_t core = hwloc_get_obj_by_type(topology, HWLOC_OBJ_CORE, tid);
hwloc_cpuset_t set = hwloc_bitmap_dup(core->cpuset);
hwloc_bitmap_singlify(set);
hwloc_set_cpubind(topology, set, HWLOC_CPUBIND_THREAD);
hwloc_bitmap_free(set);
}
and other code block is:
#pragma omp parallel num_threads(6)
{
int tid = omp_get_thread_num();
hwloc_obj_t core = hwloc_get_obj_by_type(topology, HWLOC_OBJ_PU, tid);
hwloc_cpuset_t set = hwloc_bitmap_dup(core->cpuset);
hwloc_bitmap_singlify(set);
hwloc_set_cpubind(topology, set, HWLOC_CPUBIND_THREAD);
hwloc_bitmap_free(set);
}
The goal is physically bind threads as near as possible, one thread per core. Since core ids reported on hwloc-hello.c are not consecutive and not exclusive, I suppose is better and more sure to use PU id. Or not?
2011/7/29 Samuel Thibault
<samuel.thibault@inria.fr>
Gabriele Fatigati, le Fri 29 Jul 2011 13:24:17 +0200, a écrit :
> yhanks for yout quick reply!
>
> But i have a litte doubt. in a non SMT machine, Is it better use this:
>
> hwloc_obj_t core = hwloc_get_obj_by_type(topology, HWLOC_OBJ_CORE, tid);
> hwloc_cpuset_t set = hwloc_bitmap_dup(core->cpuset);
> hwloc_bitmap_singlify(set);
> hwloc_set_cpubind(topology, set, HWLOC_CPUBIND_THREAD);
>
> or:
>
> hwloc_obj_t core = hwloc_get_obj_by_type(topology, HWLOC_OBJ_PU, tid);
> hwloc_cpuset_t set = hwloc_bitmap_dup(core->cpuset);
> hwloc_bitmap_singlify(set);
> hwloc_set_cpubind(topology, set, HWLOC_CPUBIND_THREAD);
>
> because work in the same way( i suppose).
They'll both work about the same way on SMT too, since in the end it'll
pick up only one thread. Whether you want to assign threads to cores or
threads then depends on your application: do you want to let its threads
share a core or not.
--
Ing. Gabriele Fatigati
Parallel programmer
CINECA Systems & Tecnologies Department
Supercomputing Group
Via Magnanelli 6/3, Casalecchio di Reno (BO) Italy
www.cineca.it Tel: +39 051 6171722
g.fatigati [AT]
cineca.it