[FLASH-USERS] Details of speedup after restart

[Anshu Dubey]

If you don't really need AMR, you could use FLASH3 instead. It has a true
Uniform grid with significantly less housekeeping overhead. It also
initializes the domain in parallel, so the blocks will get distributed on
as many processors as there are blocks. Otherwise as
Artur pointed out, use lrefine_min/max to be greater than 1, because FLASH 2
puts all initial blocks on the master processor, it is only the process of
refinement which distributes them.

>
> You're using only base level of refinement (lrefine_max=1) which has a non
> obvious side effect: when you start from scratch, only master procesor
> gets
> the work and the other are just waiting. After a restart the blocks are
> distributed and then the run becomes truly parallel. I'd suggest you to
> decrease nblock[xy] and use lrefine_min=2 and lrefine_max=2 instead, then
> after refining to second level the blocks will be distributed.
>
> If you don't require extremely flexible AMR then you may also increase nxb
> and nyb from 8 to 16 or 32 (at compile time) which will reduce overhead
> due
> to communication.
>
> Your setup is also relatively small - it's just 32x128 cells, so probably
> it
> makes little sense to use more than 4 or 8 CPU for it.
>
> --
> Cheers,
>         Artur
>


Anshu Dubey
Code Group Leader
phone : 773.834.2999
fax: 773.834.3230