[FLASH-USERS] Scaling problems

[Ryan Farber]

Hi Pedro,

One point of follow-up regarding your sigbus error - it looks like this is
a memory access error. I'm wondering if you're requesting more logical
cores than physical cores exist on the machine. I've found that to be
problematic in the past.

It sounds like Lee might have the answer to your issue regarding too few
zones per proc. One point I'm confused about though is whether you're
studying strong or weak scaling. Based on your response to Paco and I
checked the FLASH users guide, for uniform grid mode there's one block per
processor -- and the number of zones per block are fixed at compile time
(usually) so doesn't that mean you're increasing the amount of work
proportional to the number of processors you use? In that case, seeing a
constant "speedup" suggests good weak scaling.

Best,
--------
Ryan


On Wed, Apr 5, 2023 at 4:17 PM Leland Ellison <c.leland.ellison at gmail.com>
wrote:

> 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
>>
>>
>>
>>
>>
>> _______________________________________________
>> flash-users mailing list
>> flash-users at flash.rochester.edu
>>
>> For list info, including unsubscribe:
>> https://flash.rochester.edu/mailman/listinfo/flash-users
>>
>> _______________________________________________
>> flash-users mailing list
>> flash-users at flash.rochester.edu
>>
>> For list info, including unsubscribe:
>> https://flash.rochester.edu/mailman/listinfo/flash-users
>>
> _______________________________________________
> flash-users mailing list
> flash-users at flash.rochester.edu
>
> For list info, including unsubscribe:
> https://flash.rochester.edu/mailman/listinfo/flash-users
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://flash.rochester.edu/pipermail/flash-users/attachments/20230405/076e5b22/attachment.htm>