[Nek5000-users] question about efficient running nek5000

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

Hi Ami,

Could you try your 12 core-per-node case running with only 11 cores per 
node (and increasing the total number of nodes to keep the number of CPU 
fixed)?

Aleks

On Wed, 4 Feb 2015, 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> 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>
>>  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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>>
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>