[petsc-users] DMDA halo exchange

[Barry Smith]

  Dominic,

   I have turned the optimization on to skip the unneeded copy with the DMLocalToLocal in the branches barry/optimize-dmlocaltolocal_da and next. It passes all the PETSc tests; let me know if you see any problems.

   Barry

> On Mar 31, 2015, at 12:21 PM, Dominic Meiser <dmeiser at txcorp.com> wrote:
> 
> Great, thanks very much.
> Cheers,
> Dominic
> 
> On 03/31/2015 10:24 AM, Barry Smith wrote:
>>   Dominic,
>> 
>>     DMLocalToLocal is the intended usage. There is code inside the VecScatter to detect unneeded copies, which would result in only touching the ghost cells,  but for some reason that is not currently turned on, I'll take a look at fixing it in master.
>> 
>>   Barry
>> 
>>> On Mar 31, 2015, at 10:12 AM, Dominic Meiser <dmeiser at txcorp.com> wrote:
>>> 
>>> Hi,
>>> 
>>> I have a DMDA for a structured grid in a 3D FDTD calculation. What is the most efficient way to update the ghost regions after each time step? Currently I update a global vector and then I scatter to a local vector using DMGlobalToLocalBegin/End for the next time step. I also tried DMLocalToLocal with the same source and target vector and that appears to be slightly faster, perhaps due to better cache usage in the copy of the owned region. Ideally I would like to update just the ghost cells from the owned regions. Is there a good way to do that? Something similar to VecGhostUpdateBegin/End?
>>> 
>>> Thanks,
>>> Dominic
>>> 
>>> -- 
>>> Dominic Meiser
>>> Tech-X Corporation
>>> 5621 Arapahoe Avenue
>>> Boulder, CO 80303
>>> USA
>>> Telephone: 303-996-2036
>>> Fax: 303-448-7756
>>> www.txcorp.com
>>> 
>> 
>> 
> 
> 
> -- 
> Dominic Meiser
> Tech-X Corporation
> 5621 Arapahoe Avenue
> Boulder, CO 80303
> USA
> Telephone: 303-996-2036
> Fax: 303-448-7756
> www.txcorp.com
>