Allow the user to tweak the maximal depth of gravity tasks.

examples/parameter_example.yml

@@ -55,6 +55,7 @@ Scheduler:
   cell_sub_size_pair_grav:   256000000 # (Optional) Maximal number of interactions per sub-pair gravity task  (this is the default value).
   cell_sub_size_self_grav:   32000     # (Optional) Maximal number of interactions per sub-self gravity task  (this is the default value).
   cell_split_size:           400       # (Optional) Maximal number of particles per cell (this is the default value).
+  cell_subdepth_grav:        2         # (Optional) Maximal depth the gravity tasks can be pushed down (this is the default value).
   max_top_level_cells:       12        # (Optional) Maximal number of top-level cells in any dimension. The number of top-level cells will be the cube of this (this is the default value).
   tasks_per_cell:            0         # (Optional) The average number of tasks per cell. If not large enough the simulation will fail (means guess...).
   mpi_message_limit:         4096      # (Optional) Maximum MPI task message size to send non-buffered, KB.

src/space.c

@@ -2758,10 +2758,13 @@ void space_init(struct space *s, struct swift_params *params,
                                space_subsize_self_grav_default);
   space_splitsize = parser_get_opt_param_int(
       params, "Scheduler:cell_split_size", space_splitsize_default);
+  space_subdepth_grav = parser_get_opt_param_int(
+      params, "Scheduler:cell_subdepth_grav", space_subdepth_grav_default);
 
   if (verbose) {
     message("max_size set to %d split_size set to %d", space_maxsize,
             space_splitsize);
+    message("subdepth_grav set to %d", space_subdepth_grav);
     message("sub_size_pair_hydro set to %d, sub_size_self_hydro set to %d",
             space_subsize_pair_hydro, space_subsize_self_hydro);
     message("sub_size_pair_grav set to %d, sub_size_self_grav set to %d",