Re: [Starpu-devel] Nested codelets?

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

Sidelnik, Albert, le Wed 18 Apr 2012 08:31:18 +0200, a écrit :
> I'm working on a compiler to generate StarPU code directly from a 
> high-level parallel language. In trying to support nested parallelism from 
> this language, I'm wondering whether StarPU supports the ability to spawn 
> new codelets directly from within a currently executing codelet (assume 
> execution is only on a CPU).

Yes, you can spawn codelets. Even for the GPU case, since you have a
host part where you can run things on the CPU.

> If so, what are the main restrictions on which routines can or cannot be 
> called?

They have to be non-blocking. You can not wait for a task for instance:
it might have been assigned to the very CPU you are making wait, and
thus never complete.

> For example, can I invoke starpu_tag_notify_from_apps() from a codelet in 
> order to control the execution a successor codelet? I have not seen any 
> examples in the StarPU release that show how to do this.

Yes, you can. Simply call it.

> Also, maybe I might have missed this in the StarPU manual, but is there a 
> specific ordering on when callback functions are called for a completed 
> codelet? Can I assume that the callback will be invoked before it's 
> dependences are resolved?

No, we notify dependencies before calling the callback (and that was
missing in the doc indeed, thanks). That was made to be able to e.g.
free a dependency tag between them.

Samuel