Re: [Starpu-devel] StarPU questions

[Samuel Thibault <samuel.thibault@ens-lyon.org>]

Please always keep the mailing list in Cc, so you optimize the chance of 
getting
a complete answer in a minimized time.  Otherwise, you run the risk of either
get a terse answer, or have to wait (possibly long) that I have time to 
provide
a lengthier answer (or simply that I come back from vacations...)

Vergel, Julio, le Tue 02 Sep 2014 14:59:20 +0000, a écrit :
> I would expect a correct output if I do not add any
> "starpu_data_set_sequential_consistency_flag" and
> "starpu_task_declare_deps_array" even if I submit the tasks out of
> order

If you submit the tasks out of order, you change the sequential
consistency semantic, and thus the result.

> In other word, If I submit the tasks out of order and I do not set 
> "starpu_data_set_sequential_consistency_flag" and 
> "starpu_task_declare_deps_array", StarPU should implement the implicit 
> dependencies.

If you don't specify dependencies but submit tasks out of order, there
is no way for StarPU to know in which order the tasks are supposed to
read & write values to the handles.

> should I rely on StarPU implicit dependencies or should I always create my 
> dependencies?

It is up to your liking. Implicit dependencies allows to just submit the
tasks in sequential order and let starpu execute in parallel what can
be. Creating your dependencies allows to avoid having to submit the
tasks in the sequential order, and submit them in the order you prefer.

Samuel