[PATCH] amdgcn, nvptx: Disable OMP barriers in nested teams

[Andrew Stubbs]

On 28/09/2020 15:02, Tom de Vries wrote:
>> This patch simply skips barriers when they would "wait" for only one
>> thread (the current thread). This means that teams nested inside other
>> teams now run independently, instead of strictly in lock-step, and is
>> only valid as long as inner teams are limited to one thread each
>> (currently the case).
> 
> Is this inner-team-one-thread-limit coded or documented somewhere?

In libgomp/parallel.c, gomp_resolve_num_threads we have:

   else if (thr->ts.active_level >= 1 && !icv->nest_var)
     return 1;

> If so, it might be good to add a comment there referring to the code
> this patch adds.

   /* Accelerators with fixed thread counts require this to return 1 for
      nested parallel regions.  */

WDYT?

Andrew