netdev - Re: [PATCH net-next v2 3/10] bonding: rebuild the lock use for bond_alb

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Date:	Fri, 08 Nov 2013 17:07:30 +0100
From:	Nikolay Aleksandrov <nikolay@...hat.com>
To:	Ding Tianhong <dingtianhong@...wei.com>
CC:	Jay Vosburgh <fubar@...ibm.com>,
	Andy Gospodarek <andy@...yhouse.net>,
	"David S. Miller" <davem@...emloft.net>,
	Veaceslav Falico <vfalico@...hat.com>,
	Netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH net-next v2 3/10] bonding: rebuild the lock use for bond_alb_monitor()

On 11/08/2013 03:07 AM, Ding Tianhong wrote:
> The bond_alb_monitor use bond lock to protect the bond slave list,
> it is no effect here, we need to use RTNL or RCU to replace bond lock,
> the bond_alb_monitor will called 10 times one second, RTNL may loss
> performance here, so the bond lock replace with RCU to protect the
> bond slave list, also the RTNL is preserved, the logic of the monitor
> did not changed.
> 
> Suggested-by: Jay Vosburgh <fubar@...ibm.com>
> Suggested-by: Veaceslav Falico <vfalico@...hat.com>
> Signed-off-by: Ding Tianhong <dingtianhong@...wei.com>
> ---
>  drivers/net/bonding/bond_alb.c | 21 +++++++++------------
>  1 file changed, 9 insertions(+), 12 deletions(-)
> 
> diff --git a/drivers/net/bonding/bond_alb.c b/drivers/net/bonding/bond_alb.c
> index 1fae915..ffdb91b 100644
> --- a/drivers/net/bonding/bond_alb.c
> +++ b/drivers/net/bonding/bond_alb.c
> @@ -816,7 +816,7 @@ static void rlb_rebalance(struct bonding *bond)
>  	for (; hash_index != RLB_NULL_INDEX;
>  	     hash_index = client_info->used_next) {
>  		client_info = &(bond_info->rx_hashtbl[hash_index]);
> -		assigned_slave = rlb_next_rx_slave(bond);
> +		assigned_slave = __rlb_next_rx_slave(bond);
>  		if (assigned_slave && (client_info->slave != assigned_slave)) {
>  			client_info->slave = assigned_slave;
>  			client_info->ntt = 1;
> @@ -1495,9 +1495,10 @@ void bond_alb_monitor(struct work_struct *work)
>  	struct list_head *iter;
>  	struct slave *slave;
>  
> -	read_lock(&bond->lock);
> +	rcu_read_lock();
>  
> -	if (!bond_has_slaves(bond)) {
> +	if (!bond_has_slaves_rcu(bond)) {
> +		rcu_read_unlock();
>  		bond_info->tx_rebalance_counter = 0;
>  		bond_info->lp_counter = 0;
>  		goto re_arm;
If I'm not mistaken there's one more bond_for_each_slave() inside this function
which should be converted to RCU.

> @@ -1528,7 +1529,7 @@ void bond_alb_monitor(struct work_struct *work)
>  
>  		read_lock(&bond->curr_slave_lock);
>  
> -		bond_for_each_slave(bond, slave, iter) {
> +		bond_for_each_slave_rcu(bond, slave, iter) {
>  			tlb_clear_slave(bond, slave, 1);
>  			if (slave == bond->curr_active_slave) {
>  				SLAVE_TLB_INFO(slave).load =
> @@ -1552,11 +1553,9 @@ void bond_alb_monitor(struct work_struct *work)
>  			 * dev_set_promiscuity requires rtnl and
>  			 * nothing else.  Avoid race with bond_close.
>  			 */
> -			read_unlock(&bond->lock);
> -			if (!rtnl_trylock()) {
> -				read_lock(&bond->lock);
> +			rcu_read_unlock();
> +			if (!rtnl_trylock())
>  				goto re_arm;
> -			}
>  
>  			bond_info->rlb_promisc_timeout_counter = 0;
>  
> @@ -1568,7 +1567,7 @@ void bond_alb_monitor(struct work_struct *work)
>  			bond_info->primary_is_promisc = 0;
>  
>  			rtnl_unlock();
> -			read_lock(&bond->lock);
> +			rcu_read_lock();
>  		}
>  
>  		if (bond_info->rlb_rebalance) {
> @@ -1590,11 +1589,9 @@ void bond_alb_monitor(struct work_struct *work)
>  			}
>  		}
>  	}
> -
> +	rcu_read_unlock();
>  re_arm:
>  	queue_delayed_work(bond->wq, &bond->alb_work, alb_delta_in_ticks);
> -
> -	read_unlock(&bond->lock);
>  }
>  
>  /* assumption: called before the slave is attached to the bond
> 

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