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OpenACC Tutorial - Profiling: Difference between revisions
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What is so important about the hotspots of the code ? | What is so important about the hotspots of the code ? | ||
The Amdahl's law says that "Parallelizing the most time-consuming (i.e. the hotspots) routines will have the most impact". | The Amdahl's law says that "Parallelizing the most time-consuming (i.e. the hotspots) routines will have the most impact". | ||
== Build the Sample Code ? == | |||
For this example we will use a code from the [https://github.com/calculquebec/cq-formation-openacc repositories]. Download the package and change to the '''cpp''' or '''f90''' directory. The point of this exercise is to compile&link the code, obtain executable, and then profile them. | |||
{{Callout | |||
|title=<translate>Which compiler ?</translate> | |||
|content= | |||
<translate> | |||
As of May 2016, compiler support for OpenACC is still relatively scarce. Being pushed by [http://www.nvidia.com/content/global/global.php NVidia], through its [http://www.pgroup.com/ Portland Group] division, as well as by [http://www.cray.com/ Cray], these two lines of compilers offer the most advanced OpenACC support. [https://gcc.gnu.org/wiki/OpenACC GNU Compiler] support for OpenACC exists, but is considered experimental in version 5. It is expected to be officially supported in version 6 of the compiler. | |||
For the purpose of this tutorial, we use version 16.3 of the Portland Group compilers. We note that [http://www.pgroup.com/support/download_pgi2016.php?view=current Portland Group compilers] are free for academic usage. | |||
</translate> | |||
}} | |||
{{Command | |||
|make | |||
|result= | |||
pgc++ -fast -c -o main.o main.cpp | |||
"vector.h", line 30: warning: variable "vcoefs" was declared but never | |||
referenced | |||
double *vcoefs=v.coefs; | |||
^ | |||
pgc++ main.o -o cg.x -fast | |||
}} | |||