[Pw_forum] Questions about parallelization parameters

[Paolo Giannozzi]

1. Correct
2. There are some hints (calling them "guidelines" is an overstatement) in
the user guide. For most cases, you need only to consider parallelization
on k-points (-nk),
on bands using "task groups" (-ntg), on linear algebra (-nd).
3. The maximum number of processors for linear algebra parallelization is
the same as for PW parallelization,* before *subdivision into "task
groups". The latter are used only when computing V*psi_i and |psi_i|^2
(instead of parallelizing over PW using all processors, one parallelizes
over PW *and* band index i)

Paolo


On Sun, Aug 16, 2015 at 1:19 PM, mohammed shambakey <shambakey1 at gmail.com>
wrote:

> Hi
>
>
>    1. As I understood from user manual, the “world” of processors is
>    devided into number of “images”. Each “image” is devided into number of
>    “pools”. Each “pool” is devided into number of “bands”. “PW” level depends
>    on the least specified one of the previous four (i.e., if “band” is
>    specified, then “PW” is automatically distributed over all processor
>    available in each “band”. If “pool” is the least specified parameter, then
>    “PW” is automatically distributed over all processors available in each
>    “pool”, and so on). Prcoessors of each “PW” is devided into number of
>    “tasks” for 3D FFT. “Linear-algebra group” specifies number of processors
>    that should not exceed number of processors availabel for each “PW”, right?
>    2. Are there guidelines for the best values for the different
>    parameters (i.e., ni, nk, nb, ... etc), or I should test each problem
>    individually?
>    3. If my understanding is correct, the user manual says “nd is set to
>    1 if ScaLAPACK is not compiled, it is set to the square integer smaller
>    than or equal to half the number of processors of each pool”. But “nd”
>    should not exceed “PW”; and “PW” can be smaller than “half the number of
>    processors of each pool” using “nt”. If this case happens, will there be
>    error?
>
> Regards
>
> --
> Mohammed
>
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>



-- 
Paolo Giannozzi, Dept. Chemistry&Physics&Environment,
Univ. Udine, via delle Scienze 208, 33100 Udine, Italy
Phone +39-0432-558216, fax +39-0432-558222
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