[PATCH bpf-next 2/3] net: bonding: Use per-cpu rr_tx_counter

[Jussi Maki <joamaki@gmail.com>]

The round-robin rr_tx_counter was shared across CPUs leading
to significant cache trashing at high packet rates. This patch
switches the round-robin mechanism to use a per-cpu counter to
decide the destination device.

On a 100Gbit 64 byte packet test this reduces the CPU load from
50% to 10% on the test system.

Signed-off-by: Jussi Maki <joamaki@gmail.com>
---
 drivers/net/bonding/bond_main.c | 18 +++++++++++++++---
 include/net/bonding.h           |  2 +-
 2 files changed, 16 insertions(+), 4 deletions(-)

diff --git a/drivers/net/bonding/bond_main.c b/drivers/net/bonding/bond_main.c
index 38eea7e096f3..917dd2cdcbf4 100644
--- a/drivers/net/bonding/bond_main.c
+++ b/drivers/net/bonding/bond_main.c
@@ -4314,16 +4314,16 @@ static u32 bond_rr_gen_slave_id(struct bonding *bond)
 		slave_id = prandom_u32();
 		break;
 	case 1:
-		slave_id = bond->rr_tx_counter;
+		slave_id = this_cpu_inc_return(*bond->rr_tx_counter);
 		break;
 	default:
 		reciprocal_packets_per_slave =
 			bond->params.reciprocal_packets_per_slave;
-		slave_id = reciprocal_divide(bond->rr_tx_counter,
+		slave_id = this_cpu_inc_return(*bond->rr_tx_counter);
+		slave_id = reciprocal_divide(slave_id,
 					     reciprocal_packets_per_slave);
 		break;
 	}
-	bond->rr_tx_counter++;
 
 	return slave_id;
 }
@@ -5278,6 +5278,9 @@ static void bond_uninit(struct net_device *bond_dev)
 
 	list_del(&bond->bond_list);
 
+	if (BOND_MODE(bond) == BOND_MODE_ROUNDROBIN)
+		free_percpu(bond->rr_tx_counter);
+
 	bond_debug_unregister(bond);
 }
 
@@ -5681,6 +5684,15 @@ static int bond_init(struct net_device *bond_dev)
 	if (!bond->wq)
 		return -ENOMEM;
 
+	if (BOND_MODE(bond) == BOND_MODE_ROUNDROBIN) {
+		bond->rr_tx_counter = alloc_percpu(u32);
+		if (!bond->rr_tx_counter) {
+			destroy_workqueue(bond->wq);
+			bond->wq = NULL;
+			return -ENOMEM;
+		}
+	}
+
 	spin_lock_init(&bond->stats_lock);
 	netdev_lockdep_set_classes(bond_dev);
 
diff --git a/include/net/bonding.h b/include/net/bonding.h
index 34acb81b4234..8de8180f1be8 100644
--- a/include/net/bonding.h
+++ b/include/net/bonding.h
@@ -232,7 +232,7 @@ struct bonding {
 	char     proc_file_name[IFNAMSIZ];
 #endif /* CONFIG_PROC_FS */
 	struct   list_head bond_list;
-	u32      rr_tx_counter;
+	u32 __percpu *rr_tx_counter;
 	struct   ad_bond_info ad_info;
 	struct   alb_bond_info alb_info;
 	struct   bond_params params;
-- 
2.30.2