Add timers for matrix-free operators

[lpsaavedra]

Description of the problem

There were timers for the setup of the different components of multigrid, the application of the GMG preconditioner, but the operator timers were missing.

Description of the solution

As a follow up of #1112 , this PR adds timers for each operator and prints relevant information if set mg verbosity = extra verbose as follows:

----------------------
System operator times
----------------------
+------------------------------------------------+------------------+------------+------------------+
| Total wallclock time elapsed                   |     19.45s     3 |     19.47s |     19.48s     6 |
|                                                |                  |                               |
| Section                            | no. calls |   min time  rank |   avg time |   max time  rank |
+------------------------------------------------+------------------+------------+------------------+
| operator::evaluate_non_linear_term |         4 |   0.05946s     3 |   0.07027s |   0.07744s     0 |
| operator::evaluate_residual        |         5 |   0.08911s     0 |   0.09178s |   0.09308s     4 |
| operator::vmult                    |        53 |     1.004s     0 |     1.025s |     1.033s     6 |
+------------------------------------------------+------------------+------------+------------------+
-----------------------
Operator level 0 times
-----------------------

+------------------------------------------------+------------------+------------+------------------+
| Total wallclock time elapsed                   |      19.1s     1 |      19.1s |      19.1s     0 |
|                                                |                  |                               |
| Section                            | no. calls |   min time  rank |   avg time |   max time  rank |
+------------------------------------------------+------------------+------------+------------------+
| operator::compute_inverse_diagonal |         4 |   0.02723s     2 |   0.02774s |   0.02836s     7 |
| operator::evaluate_non_linear_term |         4 | 0.0003811s     3 | 0.0004285s | 0.0004796s     0 |
| operator::get_system_matrix        |         4 |   0.04298s     7 |   0.04391s |   0.04527s     0 |
| operator::vmult                    |       328 |   0.07959s     0 |   0.08443s |   0.08579s     6 |
+------------------------------------------------+------------------+------------+------------------+

Comments

• Useful to better understand bottlenecks and fix them.