[FLASH-USERS] Details of speedup after restart

[Sanjib Gupta]

Hi Artur,Anshu,Nathan,

Many thanks for the helpful suggestions - I will implement them later this
week when I get back to coding.......and I will be sure to share any
interesting observations with the mailing list.
But more than that, thanks enormously for taking the time to educate me
about some of the "underthe-hood" nitty-gritty of FLASH, that helps me to
understand how the code is structured and to make intelligent decisions in
future runs.
Regards,
Sanjib.


> Hi,
>
> On ¶roda, 6 czerwca 2007, sanjib gupta wrote:
>> I am attaching 2 log files - the initial run on 128 processors, then
>> immediately killing the job and restarting from the first checkpoint
>> file "hc-rt-hdf5_chk_0000"
>> notice about 4 timesteps per second initially, then ~30 timesteps/sec
>> after restart.
>
> 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
>