[Starpu-devel] [subtasks++]

[Maxim Abalenkov <maxim.abalenkov@gmail.com>]

Dear all,

I would like to re-start the conversation about subtasks. By a subtask a mean a task submitted by one of the tasks from the initial level of the task hierarchy. Once submitted it may have a number of threads designated to work on it.

I encounter this problem in the context of LU-factorisation. My implementation is panel based, where a panel is a vertical stack of rectangular matrix blocks (tiles). Consider the panel factorisation stage, that is performed on one of the panels. All task dependencies are monitored at the level of the panel. From the main algorithm I would like to launch a task responsible for the panel factorisation, who will designate a subset of threads to perform the internal operations of the factorisation in parallel. At the moment the factorisation consists of seven stages. Some of them should be performed in parallel, some of them only by a single “master” thread. I would also like to have a mechanism to synchronise the threads manually during the panel factorisation.

It may sound as a perfect example for using the SPMD task of StarPU: http://starpu.gforge.inria.fr/doc/html/TasksInStarPU.html#SPMD-modeParallelTasks. But unfortunately my experience with it hasn’t been satisfactory. The performance results are low. Are there any others developments, concepts or tools in StarPU that might help in my case? Thank you!

—

Best wishes,

Maxim

Maxim Abalenkov \\ maxim.abalenkov@gmail.com
+44 7 486 486 505 \\ http://mabalenk.gitlab.io