Subject: Re: [PATCH net-next 2/2] bonding: Simplify the xmit function for modes that use xmit_hash

From: Jay Vosburgh <[email-masked]>
Date: Wed, 03 Sep 2014 15:51:53 -0700

Mahesh Bandewar <[email-masked]> wrote:

>Earlier change to use usable slave array for TLB mode had an additional
>performance advantage. So extending the same logic to all other modes
>that use xmit-hash for slave selection (viz 802.3AD, and XOR modes).
>Also consolidating this with the earlier TLB change.
>
>The main idea is to build the usable slaves array in the control path
>and use that array for slave selection during xmit operation.
>
>Measured performance in a setup with a bond of 4x1G NICs with 200
>instances of netperf for the modes involved (3ad, xor, tlb)
>cmd: netperf -t TCP_RR -H <TargetHost> -l 60 -s 5
>
>Mode        TPS-Before   TPS-After
>
>802.3ad   : 468,694      493,101
>TLB (lb=0): 392,583      392,965
>XOR       : 475,696      484,517

	In general I think this is an improvement over traversing linked
lists; however, I have a couple of comments.

	First, for the 802.3ad mode, is the case within
bond_3ad_state_machine_handler that runs the ad_agg_selection_logic (if
the agg_select_timer runs out) handled?  This may change the active
aggregator, and thus the list of slaves that ought to be in the array,
and looking at the patch I don't see where this would be taken care of.

	As a practical matter, the usage of the agg_select_timer is such
that it's unlikely to cause a change of active aggregator (it will
usually set an active aggregator when there is none, e.g., during open
processing), but this case should probably either be handled or
commented to explain why it is safe.

	It may be that the bond_3ad_initialize call to set the
agg_select_timer to 8 seconds is no longer needed, but for now it's
there and may change the active aggregator.

	One more comment below.

>Signed-off-by: Mahesh Bandewar <[email-masked]>
>---
> drivers/net/bonding/bond_3ad.c  |  77 ++++---------------------------
> drivers/net/bonding/bond_alb.c  |  43 ++---------------
> drivers/net/bonding/bond_alb.h  |   8 ----
> drivers/net/bonding/bond_main.c | 100 ++++++++++++++++++++++++++++++++++++----
> drivers/net/bonding/bonding.h   |   8 ++++
> 5 files changed, 113 insertions(+), 123 deletions(-)
>
>diff --git a/drivers/net/bonding/bond_3ad.c b/drivers/net/bonding/bond_3ad.c
>index ee2c73a9de39..d42fd65fdfa9 100644
>--- a/drivers/net/bonding/bond_3ad.c
>+++ b/drivers/net/bonding/bond_3ad.c
>@@ -1717,6 +1717,8 @@ static void ad_enable_collecting_distributing(struct port *port)
> 			 port->actor_port_number,
> 			 port->aggregator->aggregator_identifier);
> 		__enable_port(port);
>+		if (bond_update_slave_arr(port->slave->bond, NULL))
>+			pr_debug("Failed to build slave-array for 3ad mode.\n");
> 	}
> }
> 
>@@ -1733,6 +1735,8 @@ static void ad_disable_collecting_distributing(struct port *port)
> 			 port->actor_port_number,
> 			 port->aggregator->aggregator_identifier);
> 		__disable_port(port);
>+		if (bond_update_slave_arr(port->slave->bond, NULL))
>+			pr_debug("Failed to build slave-array for 3ad mode.\n");
> 	}
> }
> 
>@@ -1917,6 +1921,9 @@ void bond_3ad_unbind_slave(struct slave *slave)
> 	__update_lacpdu_from_port(port);
> 	ad_lacpdu_send(port);
> 
>+	if (bond_update_slave_arr(bond, slave))
>+		pr_debug("Failed to build slave-array for 3AD mode.\n");
>+
> 	/* check if this aggregator is occupied */
> 	if (aggregator->lag_ports) {
> 		/* check if there are other ports related to this aggregator
>@@ -2311,6 +2318,9 @@ void bond_3ad_handle_link_change(struct slave *slave, char link)
> 	 */
> 	port->sm_vars |= AD_PORT_BEGIN;
> 
>+	if (bond_update_slave_arr(slave->bond, NULL))
>+		pr_debug("Failed to build slave-array for 3ad mode.\n");
>+
> 	__release_state_machine_lock(port);
> }
> 
>@@ -2407,73 +2417,6 @@ int bond_3ad_get_active_agg_info(struct bonding *bond, struct ad_info *ad_info)
> 	return ret;
> }
> 
>-int bond_3ad_xmit_xor(struct sk_buff *skb, struct net_device *dev)
>-{
>-	struct bonding *bond = netdev_priv(dev);
>-	struct slave *slave, *first_ok_slave;
>-	struct aggregator *agg;
>-	struct ad_info ad_info;
>-	struct list_head *iter;
>-	int slaves_in_agg;
>-	int slave_agg_no;
>-	int agg_id;
>-
>-	if (__bond_3ad_get_active_agg_info(bond, &ad_info)) {
>-		netdev_dbg(dev, "__bond_3ad_get_active_agg_info failed\n");
>-		goto err_free;
>-	}
>-
>-	slaves_in_agg = ad_info.ports;
>-	agg_id = ad_info.aggregator_id;
>-
>-	if (slaves_in_agg == 0) {
>-		netdev_dbg(dev, "active aggregator is empty\n");
>-		goto err_free;
>-	}
>-
>-	slave_agg_no = bond_xmit_hash(bond, skb) % slaves_in_agg;
>-	first_ok_slave = NULL;
>-
>-	bond_for_each_slave_rcu(bond, slave, iter) {
>-		agg = SLAVE_AD_INFO(slave)->port.aggregator;
>-		if (!agg || agg->aggregator_identifier != agg_id)
>-			continue;
>-
>-		if (slave_agg_no >= 0) {
>-			if (!first_ok_slave && bond_slave_can_tx(slave))
>-				first_ok_slave = slave;
>-			slave_agg_no--;
>-			continue;
>-		}
>-
>-		if (bond_slave_can_tx(slave)) {
>-			bond_dev_queue_xmit(bond, skb, slave->dev);
>-			goto out;
>-		}
>-	}
>-
>-	if (slave_agg_no >= 0) {
>-		netdev_err(dev, "Couldn't find a slave to tx on for aggregator ID %d\n",
>-			   agg_id);
>-		goto err_free;
>-	}
>-
>-	/* we couldn't find any suitable slave after the agg_no, so use the
>-	 * first suitable found, if found.
>-	 */
>-	if (first_ok_slave)
>-		bond_dev_queue_xmit(bond, skb, first_ok_slave->dev);
>-	else
>-		goto err_free;
>-
>-out:
>-	return NETDEV_TX_OK;
>-err_free:
>-	/* no suitable interface, frame not sent */
>-	dev_kfree_skb_any(skb);
>-	goto out;
>-}
>-
> int bond_3ad_lacpdu_recv(const struct sk_buff *skb, struct bonding *bond,
> 			 struct slave *slave)
> {
>diff --git a/drivers/net/bonding/bond_alb.c b/drivers/net/bonding/bond_alb.c
>index 73c21e233131..b2be7b3216d6 100644
>--- a/drivers/net/bonding/bond_alb.c
>+++ b/drivers/net/bonding/bond_alb.c
>@@ -200,7 +200,6 @@ static int tlb_initialize(struct bonding *bond)
> static void tlb_deinitialize(struct bonding *bond)
> {
> 	struct alb_bond_info *bond_info = &(BOND_ALB_INFO(bond));
>-	struct tlb_up_slave *arr;
> 
> 	_lock_tx_hashtbl_bh(bond);
> 
>@@ -208,10 +207,6 @@ static void tlb_deinitialize(struct bonding *bond)
> 	bond_info->tx_hashtbl = NULL;
> 
> 	_unlock_tx_hashtbl_bh(bond);
>-
>-	arr = rtnl_dereference(bond_info->slave_arr);
>-	if (arr)
>-		kfree_rcu(arr, rcu);
> }
> 
> static long long compute_gap(struct slave *slave)
>@@ -1409,39 +1404,9 @@ out:
> 	return NETDEV_TX_OK;
> }
> 
>-static int bond_tlb_update_slave_arr(struct bonding *bond,
>-				     struct slave *skipslave)
>-{
>-	struct alb_bond_info *bond_info = &(BOND_ALB_INFO(bond));
>-	struct slave *tx_slave;
>-	struct list_head *iter;
>-	struct tlb_up_slave *new_arr, *old_arr;
>-
>-	new_arr = kzalloc(offsetof(struct tlb_up_slave, arr[bond->slave_cnt]),
>-			  GFP_ATOMIC);
>-	if (!new_arr)
>-		return -ENOMEM;
>-
>-	bond_for_each_slave(bond, tx_slave, iter) {
>-		if (!bond_slave_can_tx(tx_slave))
>-			continue;
>-		if (skipslave == tx_slave)
>-			continue;
>-		new_arr->arr[new_arr->count++] = tx_slave;
>-	}
>-
>-	old_arr = rtnl_dereference(bond_info->slave_arr);
>-	rcu_assign_pointer(bond_info->slave_arr, new_arr);
>-	if (old_arr)
>-		kfree_rcu(old_arr, rcu);
>-
>-	return 0;
>-}
>-
> int bond_tlb_xmit(struct sk_buff *skb, struct net_device *bond_dev)
> {
> 	struct bonding *bond = netdev_priv(bond_dev);
>-	struct alb_bond_info *bond_info = &(BOND_ALB_INFO(bond));
> 	struct ethhdr *eth_data;
> 	struct slave *tx_slave = NULL;
> 	u32 hash_index;
>@@ -1462,9 +1427,9 @@ int bond_tlb_xmit(struct sk_buff *skb, struct net_device *bond_dev)
> 							      hash_index & 0xFF,
> 							      skb->len);
> 			} else {
>-				struct tlb_up_slave *slaves;
>+				struct bond_up_slave *slaves;
> 
>-				slaves = rcu_dereference(bond_info->slave_arr);
>+				slaves = rcu_dereference(bond->slave_arr);
> 				if (slaves && slaves->count)
> 					tx_slave = slaves->arr[hash_index %
> 							       slaves->count];
>@@ -1734,7 +1699,7 @@ void bond_alb_deinit_slave(struct bonding *bond, struct slave *slave)
> 	}
> 
> 	if (bond_is_nondyn_tlb(bond))
>-		if (bond_tlb_update_slave_arr(bond, slave))
>+		if (bond_update_slave_arr(bond, slave))
> 			pr_err("Failed to build slave-array for TLB mode.\n");
> 
> }
>@@ -1762,7 +1727,7 @@ void bond_alb_handle_link_change(struct bonding *bond, struct slave *slave, char
> 	}
> 
> 	if (bond_is_nondyn_tlb(bond)) {
>-		if (bond_tlb_update_slave_arr(bond, NULL))
>+		if (bond_update_slave_arr(bond, NULL))
> 			pr_err("Failed to build slave-array for TLB mode.\n");
> 	}
> }
>diff --git a/drivers/net/bonding/bond_alb.h b/drivers/net/bonding/bond_alb.h
>index aaeac61d03cf..5fc76c01636c 100644
>--- a/drivers/net/bonding/bond_alb.h
>+++ b/drivers/net/bonding/bond_alb.h
>@@ -139,20 +139,12 @@ struct tlb_slave_info {
> 			 */
> };
> 
>-struct tlb_up_slave {
>-	unsigned int	count;
>-	struct rcu_head rcu;
>-	struct slave	*arr[0];
>-};
>-
> struct alb_bond_info {
> 	struct tlb_client_info	*tx_hashtbl; /* Dynamically allocated */
> 	spinlock_t		tx_hashtbl_lock;
> 	u32			unbalanced_load;
> 	int			tx_rebalance_counter;
> 	int			lp_counter;
>-	/* -------- non-dynamic tlb mode only ---------*/
>-	struct tlb_up_slave __rcu *slave_arr;	  /* Up slaves */
> 	/* -------- rlb parameters -------- */
> 	int rlb_enabled;
> 	struct rlb_client_info	*rx_hashtbl;	/* Receive hash table */
>diff --git a/drivers/net/bonding/bond_main.c b/drivers/net/bonding/bond_main.c
>index f0f5eab0fab1..b0e8e7cfa10f 100644
>--- a/drivers/net/bonding/bond_main.c
>+++ b/drivers/net/bonding/bond_main.c
>@@ -1693,6 +1693,9 @@ static int __bond_release_one(struct net_device *bond_dev,
> 	if (BOND_MODE(bond) == BOND_MODE_8023AD)
> 		bond_3ad_unbind_slave(slave);
> 
>+	else if (BOND_MODE(bond) == BOND_MODE_XOR)
>+		bond_update_slave_arr(bond, slave);
>+
> 	write_unlock_bh(&bond->lock);
> 
> 	netdev_info(bond_dev, "Releasing %s interface %s\n",
>@@ -2009,6 +2012,9 @@ static void bond_miimon_commit(struct bonding *bond)
> 				bond_alb_handle_link_change(bond, slave,
> 							    BOND_LINK_UP);
> 
>+			if (BOND_MODE(bond) == BOND_MODE_XOR)
>+				bond_update_slave_arr(bond, NULL);
>+
> 			if (!bond->curr_active_slave ||
> 			    (slave == bond->primary_slave))
> 				goto do_failover;
>@@ -2037,6 +2043,9 @@ static void bond_miimon_commit(struct bonding *bond)
> 				bond_alb_handle_link_change(bond, slave,
> 							    BOND_LINK_DOWN);
> 
>+			if (BOND_MODE(bond) == BOND_MODE_XOR)
>+				bond_update_slave_arr(bond, slave);
>+
> 			if (slave == rcu_access_pointer(bond->curr_active_slave))
> 				goto do_failover;
> 
>@@ -3149,6 +3158,7 @@ static int bond_open(struct net_device *bond_dev)
> static int bond_close(struct net_device *bond_dev)
> {
> 	struct bonding *bond = netdev_priv(bond_dev);
>+	struct bond_up_slave *arr;
> 
> 	bond_work_cancel_all(bond);
> 	bond->send_peer_notif = 0;
>@@ -3156,6 +3166,10 @@ static int bond_close(struct net_device *bond_dev)
> 		bond_alb_deinitialize(bond);
> 	bond->recv_probe = NULL;
> 
>+	arr = rtnl_dereference(bond->slave_arr);
>+	if (arr)
>+	    kfree_rcu(arr, rcu);
>+
> 	return 0;
> }
> 
>@@ -3684,15 +3698,84 @@ static int bond_xmit_activebackup(struct sk_buff *skb, struct net_device *bond_d
> 	return NETDEV_TX_OK;
> }
> 
>-/* In bond_xmit_xor() , we determine the output device by using a pre-
>- * determined xmit_hash_policy(), If the selected device is not enabled,
>- * find the next active slave.
>+/* Build the usable slaves array in control path for modes that use xmit-hash
>+ * to determine the slave interface -
>+ * (a) BOND_MODE_8023AD
>+ * (b) BOND_MODE_XOR
>+ * (c) BOND_MODE_TLB && tlb_dynamic_lb == 0
>  */
>-static int bond_xmit_xor(struct sk_buff *skb, struct net_device *bond_dev)
>+int bond_update_slave_arr(struct bonding *bond, struct slave *skipslave)
> {
>-	struct bonding *bond = netdev_priv(bond_dev);
>+	struct slave *slave;
>+	struct list_head *iter;
>+	struct bond_up_slave *new_arr, *old_arr;
>+	int slaves_in_agg;
>+	int agg_id = 0;
>+	int ret = 0;
>+
>+	new_arr = kzalloc(offsetof(struct bond_up_slave, arr[bond->slave_cnt]),
>+			  GFP_ATOMIC);
>+	if (!new_arr) {
>+		ret = -ENOMEM;
>+		goto out;
>+	}

	If this allocation fails, won't the in-place array be left with
a reference to a slave that has potentially been freed, if, e.g., the
call came in via the __bond_release_one path?

	I haven't tested it, but it seems plausible that we could
resolve this by writing over the "disappearing" slave's entry in the
array, e.g., move the last element of the array to the "disappearing"
element.

	If this is a problem, the same logic exists in the current
(tlb-only) code, so a fix for stable may be needed as well.

	-J

>+	if (BOND_MODE(bond) == BOND_MODE_8023AD) {
>+		struct ad_info ad_info;
>+
>+		if (__bond_3ad_get_active_agg_info(bond, &ad_info)) {
>+			pr_debug("__bond_3ad_get_active_agg_info failed\n");
>+			kfree_rcu(new_arr, rcu);
>+			ret = -EINVAL;
>+			goto out;
>+		}
>+		slaves_in_agg = ad_info.ports;
>+		agg_id = ad_info.aggregator_id;
>+	}
>+	bond_for_each_slave(bond, slave, iter) {
>+		if (BOND_MODE(bond) == BOND_MODE_8023AD) {
>+			struct aggregator *agg;
>+
>+			agg = SLAVE_AD_INFO(slave)->port.aggregator;
>+			if (!agg || agg->aggregator_identifier != agg_id)
>+				continue;
>+		}
>+		if (!bond_slave_can_tx(slave))
>+			continue;
>+		if (skipslave == slave)
>+			continue;
>+		new_arr->arr[new_arr->count++] = slave;
>+	}
> 
>-	bond_xmit_slave_id(bond, skb, bond_xmit_hash(bond, skb) % bond->slave_cnt);
>+	old_arr = rcu_dereference_protected(bond->slave_arr,
>+					    lockdep_rtnl_is_held() ||
>+					    lockdep_is_held(&bond->lock) ||
>+					    lockdep_is_held(&bond->curr_slave_lock));
>+	rcu_assign_pointer(bond->slave_arr, new_arr);
>+	if (old_arr)
>+		kfree_rcu(old_arr, rcu);
>+
>+out:
>+	return ret;
>+}
>+
>+/* Use this Xmit function for 3AD as well as XOR modes. The current
>+ * usable slave array is formed in the control path. The xmit function
>+ * just calculates hash and sends the packet out.
>+ */
>+int bond_3ad_xor_xmit(struct sk_buff *skb, struct net_device *dev)
>+{
>+	struct bonding *bond = netdev_priv(dev);
>+	struct slave *slave;
>+	struct bond_up_slave *slaves;
>+
>+	slaves = rcu_dereference(bond->slave_arr);
>+	if (slaves && slaves->count) {
>+		slave = slaves->arr[bond_xmit_hash(bond, skb) % slaves->count];
>+		bond_dev_queue_xmit(bond, skb, slave->dev);
>+	} else {
>+		dev_kfree_skb_any(skb);
>+		atomic_long_inc(&dev->tx_dropped);
>+	}
> 
> 	return NETDEV_TX_OK;
> }
>@@ -3794,12 +3877,11 @@ static netdev_tx_t __bond_start_xmit(struct sk_buff *skb, struct net_device *dev
> 		return bond_xmit_roundrobin(skb, dev);
> 	case BOND_MODE_ACTIVEBACKUP:
> 		return bond_xmit_activebackup(skb, dev);
>+	case BOND_MODE_8023AD:
> 	case BOND_MODE_XOR:
>-		return bond_xmit_xor(skb, dev);
>+		return bond_3ad_xor_xmit(skb, dev);
> 	case BOND_MODE_BROADCAST:
> 		return bond_xmit_broadcast(skb, dev);
>-	case BOND_MODE_8023AD:
>-		return bond_3ad_xmit_xor(skb, dev);
> 	case BOND_MODE_ALB:
> 		return bond_alb_xmit(skb, dev);
> 	case BOND_MODE_TLB:
>diff --git a/drivers/net/bonding/bonding.h b/drivers/net/bonding/bonding.h
>index aace510d08d1..4a6195c0de60 100644
>--- a/drivers/net/bonding/bonding.h
>+++ b/drivers/net/bonding/bonding.h
>@@ -177,6 +177,12 @@ struct slave {
> 	struct kobject kobj;
> };
> 
>+struct bond_up_slave {
>+	unsigned int	count;
>+	struct rcu_head rcu;
>+	struct slave	*arr[0];
>+};
>+
> /*
>  * Link pseudo-state only used internally by monitors
>  */
>@@ -196,6 +202,7 @@ struct bonding {
> 	struct   slave __rcu *curr_active_slave;
> 	struct   slave __rcu *current_arp_slave;
> 	struct   slave *primary_slave;
>+	struct   bond_up_slave __rcu *slave_arr; /* Array of usable slaves */
> 	bool     force_primary;
> 	s32      slave_cnt; /* never change this value outside the attach/detach wrappers */
> 	int     (*recv_probe)(const struct sk_buff *, struct bonding *,
>@@ -527,6 +534,7 @@ const char *bond_slave_link_status(s8 link);
> struct bond_vlan_tag *bond_verify_device_path(struct net_device *start_dev,
> 					      struct net_device *end_dev,
> 					      int level);
>+int bond_update_slave_arr(struct bonding *bond, struct slave *skipslave);
> 
> #ifdef CONFIG_PROC_FS
> void bond_create_proc_entry(struct bonding *bond);
>-- 
>2.1.0.rc2.206.gedb03e5
>

---
	-Jay Vosburgh, [email-masked]