Re: [PATCH net v3 1/2] bonding: convert unbalanced_load to per-cpu state

[Nikolay Aleksandrov]

On 18/08/2026 11:47, Hangbin Liu wrote:
> From: Hangbin Liu <liuhangbin@xxxxxxxxxx>
>
> A later patch widens the bonding TLB tx counters from u32 to u64. The
> unbalanced_load counter sits in the transmit hot path, and cross-CPU
> synchronization of a u64 would introduce measurable overhead. Convert
> unbalanced_load to a per-cpu counter first so that the subsequent
> widening only touches per-cpu data local to each CPU.
>
> Introduce struct unbalanced_load_stats to hold the per-cpu counter,
> and move the aggregation into a helper, reset_unbalanced_load(), which
> sums and clears all per-cpu instances.
>
> Signed-off-by: Hangbin Liu <liuhangbin@xxxxxxxxxx>
> ---
>   drivers/net/bonding/bond_alb.c  | 25 ++++++++++++++++++-------
>   drivers/net/bonding/bond_main.c |  9 +++++++++
>   include/net/bond_alb.h          |  6 +++++-
>   3 files changed, 32 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/net/bonding/bond_alb.c b/drivers/net/bonding/bond_alb.c
> index 839f7482dc18..d54d834cf72b 100644
> --- a/drivers/net/bonding/bond_alb.c
> +++ b/drivers/net/bonding/bond_alb.c
> @@ -1345,7 +1345,7 @@ static netdev_tx_t bond_do_alb_xmit(struct sk_buff *skb, struct bonding *bond,
>   		/* unbalanced or unassigned, send through primary */
>   		tx_slave = rcu_dereference(bond->curr_active_slave);
>   		if (bond->params.tlb_dynamic_lb)
> -			bond_info->unbalanced_load += skb->len;
> +			this_cpu_add(bond_info->unbalanced_load->tx_bytes, skb->len);
>   	}
>   
>   	if (tx_slave && bond_slave_can_tx(tx_slave)) {
> @@ -1529,6 +1529,21 @@ netdev_tx_t bond_alb_xmit(struct sk_buff *skb, struct net_device *bond_dev)
>   	return bond_do_alb_xmit(skb, bond, tx_slave);
>   }
>   
> +static u32 reset_unbalanced_load(struct alb_bond_info *bond_info)
> +{
> +	struct unbalanced_load_stats *p;
> +	u32 total_bytes = 0;
> +	int i;
> +
> +	for_each_possible_cpu(i) {
> +		p = per_cpu_ptr(bond_info->unbalanced_load, i);
> +		total_bytes += READ_ONCE(p->tx_bytes);
> +		WRITE_ONCE(p->tx_bytes, 0);
> +	}
> +
> +	return total_bytes / BOND_TLB_REBALANCE_INTERVAL;
> +}
> +
>   void bond_alb_monitor(struct work_struct *work)
>   {
>   	struct bonding *bond = container_of(work, struct bonding,
> @@ -1570,12 +1585,8 @@ void bond_alb_monitor(struct work_struct *work)
>   	if (atomic_read(&bond_info->tx_rebalance_counter) >= BOND_TLB_REBALANCE_TICKS) {
>   		bond_for_each_slave_rcu(bond, slave, iter) {
>   			tlb_clear_slave(bond, slave, 1);
> -			if (slave == rcu_access_pointer(bond->curr_active_slave)) {
> -				SLAVE_TLB_INFO(slave).load =
> -					bond_info->unbalanced_load /
> -						BOND_TLB_REBALANCE_INTERVAL;
> -				bond_info->unbalanced_load = 0;
> -			}
> +			if (slave == rcu_access_pointer(bond->curr_active_slave))
> +				SLAVE_TLB_INFO(slave).load = reset_unbalanced_load(bond_info);
>   		}
>   		atomic_set(&bond_info->tx_rebalance_counter, 0);
>   	}
> diff --git a/drivers/net/bonding/bond_main.c b/drivers/net/bonding/bond_main.c
> index 522eab060f9e..9fb44e0031c8 100644
> --- a/drivers/net/bonding/bond_main.c
> +++ b/drivers/net/bonding/bond_main.c
> @@ -5995,6 +5995,7 @@ static void bond_destructor(struct net_device *bond_dev)
>   		destroy_workqueue(bond->wq);
>   
>   	free_percpu(bond->rr_tx_counter);
> +	free_percpu(bond->alb_info.unbalanced_load);
>   }
>   
>   void bond_setup(struct net_device *bond_dev)
> @@ -6494,6 +6495,10 @@ static int bond_init(struct net_device *bond_dev)
>   	if (!bond->wq)
>   		return -ENOMEM;
>   
> +	bond->alb_info.unbalanced_load = alloc_percpu(struct unbalanced_load_stats);
> +	if (!bond->alb_info.unbalanced_load)
> +		goto wq_out;
> +

The bond doesn't generally depend on this struct and shouldn't fail to init
if it fails to allocate and the user hasn't chosen alb mode. Also here is too
early to tell, the netlink mode hasn't been applied yet.
Maybe the allocation could be moved to bond_alb_initialize and the freeing to
bond_alb_deinitialize?

>   	bond->notifier_ctx = false;
>   
>   	spin_lock_init(&bond->stats_lock);
> @@ -6511,6 +6516,10 @@ static int bond_init(struct net_device *bond_dev)
>   		eth_hw_addr_random(bond_dev);
>   
>   	return 0;
> +
> +wq_out:
> +	destroy_workqueue(bond->wq);
> +	return -ENOMEM;
>   }
>   
>   unsigned int bond_get_num_tx_queues(void)
> diff --git a/include/net/bond_alb.h b/include/net/bond_alb.h
> index e5945427f38d..3fabf4714dec 100644
> --- a/include/net/bond_alb.h
> +++ b/include/net/bond_alb.h
> @@ -123,9 +123,13 @@ struct tlb_slave_info {
>   			 */
>   };
>   
> +struct unbalanced_load_stats {
> +	u32			tx_bytes;
> +};
> +
>   struct alb_bond_info {
>   	struct tlb_client_info	*tx_hashtbl; /* Dynamically allocated */
> -	u32			unbalanced_load;
> +	struct unbalanced_load_stats __percpu	*unbalanced_load;
>   	atomic_t		tx_rebalance_counter;
>   	int			lp_counter;
>   	/* -------- rlb parameters -------- */