OpenMP: conditional use of #pragma
I'm using OpenMP to improve my program efficiency on loops.
But r开发者_开发百科ecently I discovered that on small loops the use of this library decreased performances and that using the normal way was better.
In fact, I'd like to use openMP only if a condition is satisfied, my code is
#pragma omp parallel for
for (unsigned i = 0; i < size; ++i)
do_some_stuff ();
But what I want to do is to disable the #pragma if size is small enough i.e.:
if (size > OMP_MIN_VALUE)
#pragma omp parallel for
for (unsigned i = 0; i < size; ++i)
do_some_stuff ();
But does not work, the better way is to write the loop twice but I don't want to do that way...
if (size > OMP_MIN_VALUE)
{
#pragma omp parallel for
for (unsigned i = 0; i < size; ++i)
do_some_stuff ();
}
else
{
for (unsigned i = 0; i < size; ++i)
do_some_stuff ();
}
What is the better way to do that?
I think you should be able to achieve the effect you're looking for by using the optional schedule
clause on your parallel for
directive:
#pragma omp parallel for schedule(static, OMP_MIN_VALUE)
for (unsigned i = 0; i < size; ++i)
do_some_stuff ();
You might want to play around with different kinds of scheduling though and different chunk sizes to see what suits your library routines best.
精彩评论