Re: [starpu-devel] Trouble getting performance from a simple program

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

Hello Troels,

How are you? I hope all is well with you. There is a section in StarPU handbook on investigating performance issues:

  https://files.inria.fr/starpu/doc/html/CheckListWhenPerformanceAreNotThere.html

It may give you a good start.

I’m looking at the Mandelbrot example from StarPU distribution 1.4.7 (./examples/mandelbrot/mandelbrot.c). It seems there is no need to take out the graphics commands. You may run the executable with -no-x11 option. This will omit all graphics-related processing. Otherwise, I believe this should be the efficient Mandelbrot program to study.

I hope this helps you. Thank you and have a great day ahead!

—

Best wishes,

Maxim

Maxim Abalenkov \\ maxim.abalenkov@gmail.com
+44 7 486 486 505 \\ www.maxim.abalenkov.uk

On 9 Sep 2024, at 10:55, Troels Henriksen <athas@sigkill.dk> wrote:

Hello starpu-devel, I am trying to understand how to write hybrid
applications. Specifically, I have adapted the mandelbrot example from
the STarPU distribution, taken out all the graphics stuff, and added
simplistic instrumentation. I want to start by understanding
partitioning of computation (with only trivial data).

This is my program so far:
https://github.com/diku-dk/hybrid-starpu/blob/main/mandelbrot/mandelbrot.c

However, I find that my program runs very slowly on a machine with
2xA100 GPUs and two 24-core CPUs. Specifically, using nvtop I see that
the program utilises both the CPUs and the GPUs, but that the GPUs
finish the work very quickly (as expected), and a lot of time is then
spent waiting on the CPUs. I have played around with increasing the
number of blocks (for overpartitioning), but it doesn't seem to make a
significant difference. So questions are:

1) Where can I read up on the basics of load balancing in StarPU?

2) Is there already an example of an efficient Mandelbrot program (or similar
  compute-bound program) I can study?