[petsc-users] Overhead in snes function calls

[Adolfo Rodriguez]

Disregard this thread. I think the problem has to do with my data
structure.

Thanks!

On Thu, Sep 17, 2020 at 12:55 PM Adolfo Rodriguez <adantra at gmail.com> wrote:

> Sorry I was not clear before.
>
> I have to call some functions in order to assemble the Jacobian. I created
> a FormJacobian function according to the specifications and set this
> function using
>
> SNESSetJacobian <https://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/SNES/SNESSetJacobian.html#SNESSetJacobian>(snes,J,J,FormJacobian,&ctx);
>
> within FormJacobian I need to make some calls to some functions implemented in my code which is written in c++. These functions are passed through the context pointer (ctx)
>
> I noticed that when I call these functions within FormJacobian, there is an overhead which in my case is about 0.08 seconds per call and I need to make a few calls like this.
>
> I am measuring the time by doing
>
> clock_t t0;
>
> t0=clock();
>
> function call
>
> dtime = (double)(clock()-t0)/CLOCKS_PER_SEC;
>
>
> When I do this call and compute the time anywhere in y code I found dtime = x seconds, while if I make the same call inside FormJacobian I get dtime ~ x + 0.08 seconds.
>
>
> I hope the explanation is clear.
>
>
> Any clue?
>
>
> Adolfo
>
>
> On Thu, Sep 17, 2020 at 12:05 PM Matthew Knepley <knepley at gmail.com>
> wrote:
>
>> On Thu, Sep 17, 2020 at 12:00 PM Adolfo Rodriguez <adantra at gmail.com>
>> wrote:
>>
>>> I am porting a non-linear solution problem implemented explicitly to an
>>> snes implementation. Everything seems to be working fine, except for the
>>> fact that function calls done from snes to my jacobian and residual
>>> construction subroutines are slower than the regular direct call to the
>>> same subroutines (I hope this is clear). I wonder if somebody have observed
>>> this behavior and found a solution.
>>>
>>
>> It is not quite clear. I do not see a way that the calls themselves are
>> slower, but perhaps there are intervening computations? How are you timing
>> things.
>>
>>   Thanks,
>>
>>      Matt
>>
>>
>>> Regards,
>>>
>>> Adolfo
>>>
>>
>>
>> --
>> What most experimenters take for granted before they begin their
>> experiments is infinitely more interesting than any results to which their
>> experiments lead.
>> -- Norbert Wiener
>>
>> https://www.cse.buffalo.edu/~knepley/
>> <http://www.cse.buffalo.edu/~knepley/>
>>
>
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