[petsc-users] Function evaluation slowness ?

Jed Brown jed at jedbrown.org
Tue Aug 25 22:18:03 CDT 2015

Timothée Nicolas <timothee.nicolas at gmail.com> writes:
> 2. The actual problem was a very stupid one on my side. At some point I
> print small diagnostics at every time step to a text file with standard
> Fortran write statement rather than a viewer to a binary file. I had simply
> forgotten to put the statement between an if statement on the rank
> if (rank.eq.0) then
>     write(50) ....
> end if
> So all the processors were trying to write together to the file, which, I
> suppose, somehow caused all the Scatters. 

It doesn't create Scatters, but it likely creates load imbalance that
will be paid for in the subsequent VecScatter.
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