[Nek5000-users] question about efficient running nek5000

[nek5000-users at lists.mcs.anl.gov]

Ok, that gives 31k and 27k.  Those numbers are in a questionable region; you can see some scaling results for channel flow here:
http://www.mcs.anl.gov/~fischer/nek5000/sprague_nek5000_dec2010.pdf

We found great scaling for 50k or greater gridpoints per core.

I would be interested to know if the power-of-two issue is at fault here.

Mike



On Feb 4, 2015, at 12:26 PM, <nek5000-users at lists.mcs.anl.gov<mailto:nek5000-users at lists.mcs.anl.gov>>
 <nek5000-users at lists.mcs.anl.gov<mailto:nek5000-users at lists.mcs.anl.gov>> wrote:

Mike,

Thanks for your answer!, Total grid points is 32499936, which I believe it is greater than 20k for both cases!

Ami

On Wed, Feb 4, 2015 at 2:17 PM, <nek5000-users at lists.mcs.anl.gov<mailto:nek5000-users at lists.mcs.anl.gov>> wrote:
Hi Ami,

How many nodes were in your simulation? Nek scales well if your number of gridpoints per core is large enough, e.g., greater than 20K or so in my experience.

It's not clear to me if the power-of-two issue would be the cause here; perhaps Paul could comment.

Mike

On Feb 4, 2015, at 12:09 PM, <nek5000-users at lists.mcs.anl.gov<mailto:nek5000-users at lists.mcs.anl.gov>>
 wrote:

> Hi,
>
> I ran nek5000 on 1024 CPUs which is divided to 128 nodes and 8 cores per node, and the same problem on 1200 CPUs with 100 nodes and 12 cores per node, however in second case I got lower efficiency, simulation goes slower about 5~8 percent!! I ran both cases on the same cluster!! Does anyone have any idea why I do not get higher efficiency with the higher number of CPUs but less nodes involved!? Could memory be a limitation here or since numbers in first case are power of 2, it is more efficient!?
>
> Thanks,
> Ami
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