Subject: Re: [PATCH 1/5] bonding: simplify and use RCU protection for 3ad xmit path

From: Nikolay Aleksandrov <[email-masked]>
Date: Thu, 29 Aug 2013 16:25:38 +0200

On 08/28/2013 06:20 AM, Ding Tianhong wrote:
> The commit 278b20837511776dc9d5f6ee1c7fabd5479838bb
> (bonding: initial RCU conversion) has convert the roundrobin, active-backup,
> broadcast and xor xmit path to rcu protection, the performance will be better
> for these mode, so this time, convert xmit path for 3ad mode.
> 
> Signed-off-by: Ding Tianhong <[email-masked]>
> Signed-off-by: Wang Yufen <[email-masked]>
> Cc: Nikolay Aleksandrov <[email-masked]>
> Cc: Veaceslav Falico <[email-masked]>
> ---
>  drivers/net/bonding/bond_3ad.c | 31 +++++++++++++------------------
>  drivers/net/bonding/bonding.h  | 22 ++++++++++++++++++++++
>  2 files changed, 35 insertions(+), 18 deletions(-)
> 
> diff --git a/drivers/net/bonding/bond_3ad.c b/drivers/net/bonding/bond_3ad.c
> index 9010265..52d76a4 100644
> --- a/drivers/net/bonding/bond_3ad.c
> +++ b/drivers/net/bonding/bond_3ad.c
> @@ -143,7 +143,7 @@ static inline struct bonding *__get_bond_by_port(struct port *port)
>   */
>  static inline struct port *__get_first_port(struct bonding *bond)
>  {
> -	struct slave *first_slave = bond_first_slave(bond);
> +	struct slave *first_slave = bond_first_slave_rcu(bond);
>  
>  	return first_slave ? &(SLAVE_AD_INFO(first_slave).port) : NULL;
>  }
> @@ -163,7 +163,7 @@ static inline struct port *__get_next_port(struct port *port)
>  	// If there's no bond for this port, or this is the last slave
>  	if (bond == NULL)
>  		return NULL;
> -	slave_next = bond_next_slave(bond, slave);
> +	slave_next = bond_next_slave_rcu(bond, slave);
>  	if (!slave_next || bond_is_first_slave(bond, slave_next))
>  		return NULL;
>  
> @@ -2417,16 +2417,14 @@ int bond_3ad_get_active_agg_info(struct bonding *bond, struct ad_info *ad_info)
>  
>  int bond_3ad_xmit_xor(struct sk_buff *skb, struct net_device *dev)
>  {
> -	struct slave *slave, *start_at;
> +	struct slave *slave;
Please re-arrange longest -> shortest where possible.

>  	struct bonding *bond = netdev_priv(dev);
>  	int slave_agg_no;
>  	int slaves_in_agg;
>  	int agg_id;
> -	int i;
>  	struct ad_info ad_info;
>  	int res = 1;
>  
> -	read_lock(&bond->lock);
>  	if (__bond_3ad_get_active_agg_info(bond, &ad_info)) {
>  		pr_debug("%s: Error: __bond_3ad_get_active_agg_info failed\n",
>  			 dev->name);
> @@ -2444,13 +2442,16 @@ int bond_3ad_xmit_xor(struct sk_buff *skb, struct net_device *dev)
>  
>  	slave_agg_no = bond->xmit_hash_policy(skb, slaves_in_agg);
>  
> -	bond_for_each_slave(bond, slave) {
> +	bond_for_each_slave_rcu(bond, slave) {
>  		struct aggregator *agg = SLAVE_AD_INFO(slave).port.aggregator;
>  
>  		if (agg && (agg->aggregator_identifier == agg_id)) {
> -			slave_agg_no--;
> -			if (slave_agg_no < 0)
> -				break;
> +			if (--slave_agg_no < 0) {
> +				if (SLAVE_IS_OK(slave)) {
> +					res = bond_dev_queue_xmit(bond, skb, slave->dev);
> +					goto out;
> +				}
> +			}
>  		}
>  	}
>  
> @@ -2460,23 +2461,17 @@ int bond_3ad_xmit_xor(struct sk_buff *skb, struct net_device *dev)
>  		goto out;
>  	}
>  
> -	start_at = slave;
> -
> -	bond_for_each_slave_from(bond, slave, i, start_at) {
> -		int slave_agg_id = 0;
> +	bond_for_each_slave_rcu(bond, slave) {
>  		struct aggregator *agg = SLAVE_AD_INFO(slave).port.aggregator;
>  
> -		if (agg)
> -			slave_agg_id = agg->aggregator_identifier;
> -
> -		if (SLAVE_IS_OK(slave) && agg && (slave_agg_id == agg_id)) {
> +		if (SLAVE_IS_OK(slave) && agg &&
> +				(agg->aggregator_identifier == agg_id)) {
Please drop the ( ) from (agg->aggregator_identifier == agg_id), also align it
properly.

>  			res = bond_dev_queue_xmit(bond, skb, slave->dev);
>  			break;
>  		}
>  	}
>  
>  out:
> -	read_unlock(&bond->lock);
>  	if (res) {
>  		/* no suitable interface, frame not sent */
>  		kfree_skb(skb);
> diff --git a/drivers/net/bonding/bonding.h b/drivers/net/bonding/bonding.h
> index 4bf52d5..ecb5d1d 100644
> --- a/drivers/net/bonding/bonding.h
> +++ b/drivers/net/bonding/bonding.h
> @@ -74,6 +74,9 @@
>  /* slave list primitives */
>  #define bond_to_slave(ptr) list_entry(ptr, struct slave, list)
>  
> +/* slave list primitives, Caller must hold rcu_read_lock */
> +#define bond_to_slave_rcu(ptr) list_entry_rcu(ptr, struct slave, list)
> +
>  /* IMPORTANT: bond_first/last_slave can return NULL in case of an empty list */
>  #define bond_first_slave(bond) \
>  	list_first_entry_or_null(&(bond)->slave_list, struct slave, list)
> @@ -81,6 +84,16 @@
>  	(list_empty(&(bond)->slave_list) ? NULL : \
>  					   bond_to_slave((bond)->slave_list.prev))
>  
> +/**
> + * IMPORTANT: bond_first/last_slave_rcu can return NULL in case of an empty list
> + * Caller must hold rcu_read_lock
> + */
Styling nit: the comments in net/ should be /* text...

> +#define bond_first_slave_rcu(bond) \
> +	list_first_or_null_rcu(&(bond)->slave_list, struct slave, list)
> +#define bond_last_slave_rcu(bond) \
> +	(list_emptry(&(bond)->slave_list) ? NULL : \
^^^^^^^^^^^^^^^^^^^^^
Did you compile this ?

> +						bond_to_slave_rcu((bond)->slave_list.prev))
> +
>  #define bond_is_first_slave(bond, pos) ((pos)->list.prev == &(bond)->slave_list)
>  #define bond_is_last_slave(bond, pos) ((pos)->list.next == &(bond)->slave_list)
>  
> @@ -93,6 +106,15 @@
>  	(bond_is_first_slave(bond, pos) ? bond_last_slave(bond) : \
>  					  bond_to_slave((pos)->list.prev))
>  
> +/* Since bond_first/last_slave_rcu can return NULL, these can return NULL too */
> +#define bond_next_slave_rcu(bond, pos) \
> +	(bond_is_last_slave(bond, pos) ? bond_first_slave_rcu(bond) : \
> +					 bond_to_slave_rcu((pos)->list.next))
> +
> +#define bond_prev_slave_rcu(bond, pos) \
> +	(bond_is_first_slave(bond, pos) ? bond_last_slave_rcu(bond) : \
> +					  bond_to_slave_rcu((pos)->list.prev))
> +
>  /**
>   * bond_for_each_slave_from - iterate the slaves list from a starting point
>   * @bond:	the bond holding this list.
>