[Pw_forum] Low speed

[mohsen modaresi]

Dear Baris
Thanks a lot for your answer.
 how many scf steps
"do you perform in these 3 hours? Does your system have some
convergence problems?", It take 12 iteration to perform, And there is
no convergence problem
"This is especially important if you are using a low memory
bandwidth architecture.", I can not understand your hint, We use a P4
machine with 8 core, I think you say we must use Half of them, Is it
true?
And finally thanks for your answer
Moshen Modaresi


On 5/20/10, O. Baris Malcioglu <baris.malcioglu at gmail.com> wrote:
> Dear Mohsen,
> Please notice that you have asked a rather vague question regarding
> performance,
>
> First of all, please notice that since PW is a plane wave code, it is
> not just the number of atoms that determine the "size" of the system.
> You have to take into account the number of plane waves you are using.
> This depends on your cutoffs and simulation supercell. Exaggerating
> the situation unnecessarily, for example putting only an ethane
> molecule in a 500x500x500 Bohr box (even with modest cutoff) will
> result in a system size that will certainly give a hard time to the
> computer you are describing. In the same sense, using very high
> cutoffs will lead to same problem.
>
> Secondly, "3 hours" is not a good enough criteria, how many scf steps
> do you perform in these 3 hours? Does your system have some
> convergence problems?
>
> Finally, 8 cpu is not a good enough identification nowadays, if the
> "cpu" you are mentioning is due to hyper-threading, it is usually
> better if you use only 4, since you waste your precious memory
> bandwidth. This is especially important if you are using a low memory
> bandwidth architecture.
>
> Some general guidelines :
>
> -Make sure that your computer is not using swap,
> -Use architecture dependent acceleration libraries such as MKL. For
> example you can setup fftw 3.x to utilize instruction sets such as
> sse2.
> -If this is a parallel compiler check wall times, how much do you
> loose communicating?
>
> Best,
> Baris
>
> 2010/5/20 Phillip Nyawere <pnyawere at gmail.com>:
>> You need high speed computer. I tried with 96 atoms and it was taking even
>> longer.
>> Success.
>>
>> On Wed, May 12, 2010 at 10:07 PM, mohsen modaresi
>> <modaresi.mohsen at gmail.com> wrote:
>>>
>>> Dear Developers and users,
>>> I run a SCF calculation with 71 atoms on a camputer with 8 cpu and 8GB
>>> RAM, i expect it run in some minutes, But it take 3 hours to run.
>>> Is it regular?
>>>
>>>
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>>
>>
>>
>> --
>> Phillip W. Otieno Nyawere,
>> Kabarak University,
>> Dept of Physics & Mathematics,
>> P.O Box Private Bag - 20157,
>> Kabarak, Kenya.
>> Tel +254728342054
>> pnyawere at gmail.com, potieno at kabarak.ac.ke
>>
>> The battle belongs to the Lord.
>>
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>>
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