GCC OpenAcc executables problems

[Alexander Monakov]

On Thu, 14 Jan 2016, Esteban Hernández wrote:

> On Thu, Jan 14, 2016 at 4:35 PM, Esteban Hernández <eshernan@gmail.com> wrote:
> > Dear alexander,
> >
> > I review the code of pi implementation  and the pi value is copyout
> >
> >
> >         #pragma acc data copyout (pi)
> >         #pragma acc parallel vector_length (vl)  reduction (+:pi)
> >         for (i=0; i<N; i++) {
> >             double t= (double)((i+0.5)/N);
> >             pi +=4.0/(1.0+t*t);
> >          }
> >         printf("pi=%11.10f\n",pi/N);
> >
> > But when  i run the program with strace the result is wattling forever,

It's probably just takes a lot of time (it's running only with 1 worker&gang),
try decreasing N or add num_workers/num_gangs clauses in addition to
vector_length.

(I'm not sure if OpenACC requires running with 1 worker and gang in your
example, or GCC is behaving suboptimally -- please wait for comment from
OpenACC implementors in GCC)

Alexander