[petsc-dev] making DA more light weight

[Barry Smith]

On May 15, 2014, at 5:42 PM, Jed Brown <jed at jedbrown.org> wrote:

> Barry Smith <bsmith at mcs.anl.gov> writes:
> 
>>  I suggest the following:  
>> 
>>    ISLocalToGlobalCreate() takes a block size. 
>> 
>>    ISLocalToGlobalApply() will then do the integer arithmetic if bs > 1
>> 
>>    ISLocalToGlobalApplyBlock() will just use the given indices 
>> 
>>   Then Mat/VecSetLocalToGlobal() will only have one mapping and DMDACreate() will only create the block version 
> 
> That's what I meant in my other mail (rationalizing that integer
> division should not ruin performance; needs to be tested).

    Yes I know it is what you said, I was just laying out in more detail the API changes.

>  I think this
> is worthwhile and not hard, but it's small fish compared to VecScatter,
> which requires several times as much memory.  

    Not true

> See my other mail with
> full stack traces for each large allocation.

    See my other email where I explained that since you ran in the debugger on one process you got very different results then you would get on two processes.

   Barry