Re: [PATCH v2 2/2] bonding: reuse neigh_setup from slave neigh_parms

[Kuniyuki Iwashima <kuniyu@google.com>]

From: Paritosh Potukuchi <paritoshpotukuchi@gmail.com>
Date: Wed,  1 Jul 2026 08:16:00 +0000
> bond_neigh_init() currently relies on the slave device's
> ndo_neigh_setup() callback to obtain a neigh_setup() handler.
> 
> When an initialized neigh_parms instance already exists for the
> slave device, reuse the neigh_setup() callback stored in it instead
> of invoking ndo_neigh_setup() again.
> 
> If no neigh_parms instance is found, or no neigh_setup() callback is
> present, retain the existing ndo_neigh_setup() fallback path.
> 
> This avoids unnecessary ndo_neigh_setup() invocations while preserving
> existing behaviour.
> 
> Signed-off-by: Paritosh Potukuchi <paritosh.potukuchi@amd.com>
> ---
>  drivers/net/bonding/bond_main.c | 10 +++++++++-
>  1 file changed, 9 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/net/bonding/bond_main.c b/drivers/net/bonding/bond_main.c
> index e044fc733b8c..d2e4dae4e97c 100644
> --- a/drivers/net/bonding/bond_main.c
> +++ b/drivers/net/bonding/bond_main.c
> @@ -4719,7 +4719,7 @@ static int bond_neigh_init(struct neighbour *n)
>  {
>  	struct bonding *bond = netdev_priv(n->dev);
>  	const struct net_device_ops *slave_ops;
> -	struct neigh_parms parms;
> +	struct neigh_parms parms, *p;
>  	struct slave *slave;
>  	int ret = 0;
>  
> @@ -4727,6 +4727,14 @@ static int bond_neigh_init(struct neighbour *n)
>  	slave = bond_first_slave_rcu(bond);
>  	if (!slave)
>  		goto out;
> +
> +	p = neigh_parms_lookup_dev(n->tbl, slave->dev);

This introduces O(n) list traversal while it can be done
with fixed costs (3 dereferences + 1 call).

Since neigh_table is global (arp_tbl or nd_tbl), the O(n)
list traversal could take longer and rather de-optimise.


> +
> +	if (p && p->neigh_setup) {
> +		ret = p->neigh_setup(n);
> +		goto out;
> +	}
> +
>  	slave_ops = slave->dev->netdev_ops;
>  	if (!slave_ops->ndo_neigh_setup)
>  		goto out;
> -- 
> 2.43.0