Time for MatAssembly

[tribur at vision.ee.ethz.ch]

Distinguished PETSc experts,

Assuming processor k has defined N entries of a parallel matrix using  
MatSetValues. The half of the entries are in matrix rows belonging to  
this processor, but the other half are situated in rows of other  
processors.

My question:

When does MatAssemblyBegin+MatAssemblyEnd take longer, if the rows  
where the second half of the entries are situated belong all to one  
single other processor, e.g. processor k+1, or if these rows are  
distributed across several, let's say 4, other processors? Is there a  
significant difference?

Thanks in advance for your answer,
Trini