Re: [Starpu-devel] Could STARPU_COMMUTE change order with a single worker ?

[Samuel Thibault <samuel.thibault@inria.fr>]

Hello,

Jerome Robert, on jeu. 16 févr. 2017 12:04:11 +0100, wrote:
> With multiple worker, inserting T1 then T2, with both allowed to commute 
> (STARPU_COMMUTE flag), could lead to and execution order of T1-T2 or T2-T1. 
> But with only one worker (STARPU_NCPU=1), does the current implementation 
> will always execute T1-T2 (same as insertion order) or could they be 
> reordered ?

There is nothing that prevents a reordering, but in practice they
will probably be always in order: I guess in your case they are
immediately ready for execution?  In that case the dependency stages in
_starpu_enforce_deps_and_schedule() return immediately, and the task is
thus pushed to the scheduler from the starpu_task_submit() call, and
thus before starpu_task_submit returns. Then it's up to the scheduler of
course, but they usually keep the tasks in submission order. In the case
of prio, two tasks with the same priority seem to be kept in order.

Samuel