[petsc-dev] PetscObjectViewFromOptions() pull request 1005 1006

[Lawrence Mitchell]

> On 28 Jun 2018, at 16:51, Smith, Barry F. <bsmith at mcs.anl.gov> wrote:
> 
> 
>   I am having trouble tracking the following issue (and people's opinion on it) in the pull requests so I am starting an email thread to discuss the issue.
> 
>   Currently - (this is my understanding)
> 
> 1)   PetscObjectViewFromOptions() is very slow
> 2)   Many calls are made to this routine directly from solvers (such as KSP)

It is particularly insidious in the PC under discussion in the PR#1005, because we have O(dofs) KSPs, not O(1).

>  because of this there is a configure option to turn off checking of PetscObjectViewFromOptions


> In pull request 1005 Matt moved the PetscObjectViewFromOptions() routines out of KSPSolve() and put them in KSPSetFromOptions(). 
> 
> In pull request 1006 Lisandro proposes moving the configure option to turn off checking of  a PetscObjectViewFromOptions() to a runtime option.

This uses the Push/Pop stuff that I added in PR#604, in response to noting (in PCPATCH runs) that 90% of the time was spent in XXXViewFromOptions.  After adding the push/pop pair, this dropped to basically 0%.  I didn't do further exhaustive benchmarking to check for further problems.

The PCPATCH code already uses push/pop, so I don't know where Matt saw all this slow options checking that kicked off this discussion.

Cheers,

Lawrence