[PATCH net-next] net: bonding: Use per-cpu rr_tx_counter

[PATCH net-next] net: bonding: Use per-cpu rr_tx_counter

[Jussi Maki]

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

On a test with 2x100Gbit ICE nic with pktgen_sample_04_many_flows.sh
(-s 64 -t 32) the tx rate was 19.6Mpps before and 22.3Mpps after
this patch.

"perf top -e cache_misses" before:
    12.31%  [bonding]       [k] bond_xmit_roundrobin_slave_get
    10.59%  [sch_fq_codel]  [k] fq_codel_dequeue
     9.34%  [kernel]        [k] skb_release_data
after:
    15.42%  [sch_fq_codel]  [k] fq_codel_dequeue
    10.06%  [kernel]        [k] __memset
     9.12%  [kernel]        [k] skb_release_data

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 eb79a9f05914..1d9137e77dfc 100644
--- a/drivers/net/bonding/bond_main.c
+++ b/drivers/net/bonding/bond_main.c
@@ -4202,16 +4202,16 @@ 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;
 }
@@ -4852,6 +4852,9 @@ static void bond_destructor(struct net_device *bond_dev)
 
 	if (bond->wq)
 		destroy_workqueue(bond->wq);
+
+	if (bond->rr_tx_counter)
+		free_percpu(bond->rr_tx_counter);
 }
 
 void bond_setup(struct net_device *bond_dev)
@@ -5350,6 +5353,15 @@ 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 019e998d944a..15335732e166 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

Re: [PATCH net-next] net: bonding: Use per-cpu rr_tx_counter

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to netdev/net-next.git (refs/heads/master):

On Tue, 15 Jun 2021 08:54:15 +0000 you wrote:
> The round-robin rr_tx_counter was shared across CPUs leading to
> significant cache thrashing at high packet rates. This patch switches
> the round-robin packet counter to use a per-cpu variable to decide
> the destination slave.
> 
> On a test with 2x100Gbit ICE nic with pktgen_sample_04_many_flows.sh
> (-s 64 -t 32) the tx rate was 19.6Mpps before and 22.3Mpps after
> this patch.
> 
> [...]

Here is the summary with links:
  - [net-next] net: bonding: Use per-cpu rr_tx_counter
    https://git.kernel.org/netdev/net-next/c/848ca9182a7d

You are awesome, thank you!
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