[FLASH-USERS] Scaling problems

[Leland Ellison]

Hi Pedro,

I suspect your per-block zone counts are too low to see benefits of adding
more procs at this point. The details will depend on your specific problem
and hardware of course, but when I've done strong scaling studies I've
found (rapidly) diminishing returns to adding more procs once I fall below
about ~1000 zones per proc. I think this is what you're seeing in your
nxb=nxy=16 and nxb=nxy=28 cases. If your scaling study continues up to
several thousand zones per proc, I bet you'll see more of the expected
behavior.

Hope this helps!
Lee

 ________________
Leland Ellison PhD
Computational Physicist
https://www.linkedin.com/in/clelandellison/
https://scholar.google.com/citations?user=1rfcVWgAAAAJ

On Wed, Apr 5, 2023 at 6:46 AM pedro romero <
pedro.romero at greentownsbyfusion.com> wrote:

> Hi Paco,
>
>
>
> As far as I know, using uniform grid fixes the number of blocks as one per
> processor. Am I wrong? Do you mean to fix nxb and nyb while varying the
> cores?
>
>
>
> *De:* Francisco Holguin <opaco at umich.edu>
> *Enviado el:* miércoles, 5 de abril de 2023 15:17
> *Para:* pedro romero <pedro.romero at greentownsbyfusion.com>
> *CC:* flash-users at flash.rochester.edu
> *Asunto:* Re: [FLASH-USERS] Scaling problems
>
>
>
> Hi Pedro,
>
>
>
> What if you just fix the number of blocks, and vary the cores?
>
>
>
> -Paco
>
>
>
> On Wed, Apr 5, 2023 at 5:13 AM pedro romero <
> pedro.romero at greentownsbyfusion.com> wrote:
>
> Hi all,
>
>
>
> I am trying to scale up on computational resources and I came across a few
> issues. First of all, I am running the same +ug example (a modification of
> 2D Zpinch template) varying the number of cores, nxb and nyb but it shows
> no speed up as the number of cores increase (I am tuning Iprocs, Jprocs,
> nxb and nyb to always get an approximately equal grid).
>
>
>
> Furthermore, at a certain number of cores the program execution
> interrupts, and I get a SIGBUS error (which I attach to this message). Am I
> missing something? Is there any additional thing to consider?
>
>
>
> I will also attach the log file of one successful run using 36 cores and
> nxb=nyb=16 (which shows little or no speed up in comparison to a run on 12
> cores and nxb=nyb=28). Thank you in advance for any help.
>
>
>
> Pedro
>
>
>
>
>
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