mlxsw: spectrum_router: Only query neighbour activity when necessary

The driver periodically queries the device for activity of neighbour
entries in order to report it to the kernel's neighbour table.

Avoid unnecessary activity query when no neighbours are installed. Use
an atomic variable to track the number of neighbours, as it is read
without any locks.

Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Reviewed-by: Petr Machata <petrm@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/mellanox/mlxsw/spectrum_router.c

@@ -2360,6 +2360,7 @@ mlxsw_sp_neigh_entry_create(struct mlxsw_sp *mlxsw_sp, struct neighbour *n)
 		goto err_neigh_entry_insert;
 
 	mlxsw_sp_neigh_counter_alloc(mlxsw_sp, neigh_entry);
+	atomic_inc(&mlxsw_sp->router->neighs_update.neigh_count);
 	list_add(&neigh_entry->rif_list_node, &rif->neigh_list);
 
 	return neigh_entry;
@@ -2374,6 +2375,7 @@ mlxsw_sp_neigh_entry_destroy(struct mlxsw_sp *mlxsw_sp,
 			     struct mlxsw_sp_neigh_entry *neigh_entry)
 {
 	list_del(&neigh_entry->rif_list_node);
+	atomic_dec(&mlxsw_sp->router->neighs_update.neigh_count);
 	mlxsw_sp_neigh_counter_free(mlxsw_sp, neigh_entry);
 	mlxsw_sp_neigh_entry_remove(mlxsw_sp, neigh_entry);
 	mlxsw_sp_neigh_entry_free(neigh_entry);
@@ -2571,6 +2573,9 @@ static int mlxsw_sp_router_neighs_update_rauhtd(struct mlxsw_sp *mlxsw_sp)
 	char *rauhtd_pl;
 	int err;
 
+	if (!atomic_read(&mlxsw_sp->router->neighs_update.neigh_count))
+		return 0;
+
 	rauhtd_pl = kmalloc(MLXSW_REG_RAUHTD_LEN, GFP_KERNEL);
 	if (!rauhtd_pl)
 		return -ENOMEM;
@@ -2950,6 +2955,7 @@ static int mlxsw_sp_neigh_init(struct mlxsw_sp *mlxsw_sp)
 			  mlxsw_sp_router_neighs_update_work);
 	INIT_DELAYED_WORK(&mlxsw_sp->router->nexthop_probe_dw,
 			  mlxsw_sp_router_probe_unresolved_nexthops);
+	atomic_set(&mlxsw_sp->router->neighs_update.neigh_count, 0);
 	mlxsw_core_schedule_dw(&mlxsw_sp->router->neighs_update.dw, 0);
 	mlxsw_core_schedule_dw(&mlxsw_sp->router->nexthop_probe_dw, 0);
 	return 0;

drivers/net/ethernet/mellanox/mlxsw/spectrum_router.h

@@ -56,6 +56,7 @@ struct mlxsw_sp_router {
 	struct {
 		struct delayed_work dw;
 		unsigned long interval;	/* ms */
+		atomic_t neigh_count;
 	} neighs_update;
 	struct delayed_work nexthop_probe_dw;
 #define MLXSW_SP_UNRESOLVED_NH_PROBE_INTERVAL 5000 /* ms */