[Pw_forum] PW taskgroups and a large run on a BG/P

[Nichols A. Romero]

David,

You should really start by making estimates of how much memory your
calculation needs. To
do that you will really need to understand the algorithm otherwise you will
just end up playing with
parameters forever.

ntg is for band parallelization. You have 2560 electrons.

ntg = 32 is probably too large.

Maybe somebody on this list can make a suggestion? My experience with a
real-space code is
the more bands per processor the better. You will probably want at least
250-500 bands per processor.

On Wed, Jan 28, 2009 at 4:20 PM, Nichols A. Romero <naromero at gmail.com>wrote:

> David,
>
> You have the:
> ortho sub group set to 32*32
>
> Paolo can correct me if I am wrong. This is the Scalapack blacs grid for
> the
> cholesky decomposition. It basically takes the overlap matrix whose
> dimensions
> are (number of states) by (number of states) and divides into 32-by-32
> pieces
> according to a 2D block cyclic algorithm. You are using 32*32=1024
> processors
> to do the cholesky decomposition of a 2560-by-2560.
>
> I would recommend using something like 8*8.
>
> On Wed, Jan 28, 2009 at 4:08 PM, <giannozz at democritos.it> wrote:
>
>> Quoting David Farrell <davidfarrell2008 at u.northwestern.edu>:
>>
>> > I am trying to run a 1152 atom, 2560 electron pw MD system on a BG/P,
>> >  and I believe I am running up against memory issues
>>
>> set nbnd, diago_david_ndim, mixing_ndim to the smallest possible
>> values to save memory. Use the CVS version and try to compile scalapack
>> (instructions in the wiki) if you have trouble with subspace
>> diagonalization, or else use a smaller set of processors in the "ortho
>> group": 1024 seems to me a lot for a system with O(1000) states.
>>
>> Paolo
>>
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>
>
>
> --
> Nichols A. Romero, Ph.D.
> Argonne Leadership Computing Facility
> Argonne, IL 60490
> (630) 252-3441 (O)
> (630) 470-0462 (C)
>
>


-- 
Nichols A. Romero, Ph.D.
Argonne Leadership Computing Facility
Argonne, IL 60490
(630) 252-3441 (O)
(630) 470-0462 (C)
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