netdev - Re: [patch net-next-2.6 V3] net: convert bonding to use rx

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Date:	Sat, 19 Feb 2011 12:28:43 +0100
From:	Jiri Pirko <jpirko@...hat.com>
To:	Nicolas de Pesloüan 
	<nicolas.2p.debian@...il.com>
Cc:	Jay Vosburgh <fubar@...ibm.com>,
	David Miller <davem@...emloft.net>, kaber@...sh.net,
	eric.dumazet@...il.com, netdev@...r.kernel.org,
	shemminger@...ux-foundation.org, andy@...yhouse.net
Subject: Re: [patch net-next-2.6 V3] net: convert bonding to use rx_handler

Sat, Feb 19, 2011 at 12:08:31PM CET, jpirko@...hat.com wrote:
>Sat, Feb 19, 2011 at 11:56:23AM CET, nicolas.2p.debian@...il.com wrote:
>>Le 19/02/2011 09:05, Jiri Pirko a écrit :
>>>This patch converts bonding to use rx_handler. Results in cleaner
>>>__netif_receive_skb() with much less exceptions needed. Also
>>>bond-specific work is moved into bond code.
>>>
>>>Signed-off-by: Jiri Pirko<jpirko@...hat.com>
>>>
>>>v1->v2:
>>>         using skb_iif instead of new input_dev to remember original
>>>	device
>>>v2->v3:
>>>	set orig_dev = skb->dev if skb_iif is set
>>>
>>
>>Why do we need to let the rx_handlers call netif_rx() or __netif_receive_skb()?
>>
>>Bonding used to be handled with very few overhead, simply replacing
>>skb->dev with skb->dev->master. Time has passed and we eventually
>>added many special processing for bonding into __netif_receive_skb(),
>>but the overhead remained very light.
>>
>>Calling netif_rx() (or __netif_receive_skb()) to allow nesting would probably lead to some overhead.
>>
>>Can't we, instead, loop inside __netif_receive_skb(), and deliver
>>whatever need to be delivered, to whoever need, inside the loop ?
>>
>>rx_handler = rcu_dereference(skb->dev->rx_handler);
>>while (rx_handler) {
>>	/* ...  */
>>	orig_dev = skb->dev;
>>	skb = rx_handler(skb);
>>	/* ... */
>>	rx_handler = (skb->dev != orig_dev) ? rcu_dereference(skb->dev->rx_handler) : NULL;
>>}
>>
>>This would reduce the overhead, while still allowing nesting: vlan on
>>top on bonding, bridge on top on bonding, ...
>
>I see your point. Makes sense to me. But the loop would have to include
>at least processing of ptype_all too. I'm going to cook a follow-up
>patch.
>

DRAFT (doesn't modify rx_handlers):

diff --git a/net/core/dev.c b/net/core/dev.c
index 4ebf7fe..e5dba47 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -3115,6 +3115,7 @@ static int __netif_receive_skb(struct sk_buff *skb)
 {
 	struct packet_type *ptype, *pt_prev;
 	rx_handler_func_t *rx_handler;
+	struct net_device *dev;
 	struct net_device *orig_dev;
 	struct net_device *null_or_dev;
 	int ret = NET_RX_DROP;
@@ -3129,7 +3130,9 @@ static int __netif_receive_skb(struct sk_buff *skb)
 	if (netpoll_receive_skb(skb))
 		return NET_RX_DROP;
 
-	__this_cpu_inc(softnet_data.processed);
+	skb->skb_iif = skb->dev->ifindex;
+	orig_dev = skb->dev;
+
 	skb_reset_network_header(skb);
 	skb_reset_transport_header(skb);
 	skb->mac_len = skb->network_header - skb->mac_header;
@@ -3138,12 +3141,9 @@ static int __netif_receive_skb(struct sk_buff *skb)
 
 	rcu_read_lock();
 
-	if (!skb->skb_iif) {
-		skb->skb_iif = skb->dev->ifindex;
-		orig_dev = skb->dev;
-	} else {
-		orig_dev = dev_get_by_index_rcu(dev_net(skb->dev), skb->skb_iif);
-	}
+another_round:
+	__this_cpu_inc(softnet_data.processed);
+	dev = skb->dev;
 
 #ifdef CONFIG_NET_CLS_ACT
 	if (skb->tc_verd & TC_NCLS) {
@@ -3153,7 +3153,7 @@ static int __netif_receive_skb(struct sk_buff *skb)
 #endif
 
 	list_for_each_entry_rcu(ptype, &ptype_all, list) {
-		if (!ptype->dev || ptype->dev == skb->dev) {
+		if (!ptype->dev || ptype->dev == dev) {
 			if (pt_prev)
 				ret = deliver_skb(skb, pt_prev, orig_dev);
 			pt_prev = ptype;
@@ -3167,7 +3167,7 @@ static int __netif_receive_skb(struct sk_buff *skb)
 ncls:
 #endif
 
-	rx_handler = rcu_dereference(skb->dev->rx_handler);
+	rx_handler = rcu_dereference(dev->rx_handler);
 	if (rx_handler) {
 		if (pt_prev) {
 			ret = deliver_skb(skb, pt_prev, orig_dev);
@@ -3176,6 +3176,8 @@ ncls:
 		skb = rx_handler(skb);
 		if (!skb)
 			goto out;
+		if (dev != skb->dev)
+			goto another_round;
 	}
 
 	if (vlan_tx_tag_present(skb)) {
--
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