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

Sat, Feb 19, 2011 at 02:18:00PM CET, nicolas.2p.debian@gmail.com wrote:

Le 19/02/2011 12:28, Jiri Pirko a écrit :

quoted

Sat, Feb 19, 2011 at 12:08:31PM CET, jpirko@redhat.com wrote:

quoted

Sat, Feb 19, 2011 at 11:56:23AM CET, nicolas.2p.debian@gmail.com wrote:

quoted

Le 19/02/2011 09:05, Jiri Pirko a écrit :

quoted

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<redacted>

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;

orig_dev should be set inside the loop, to reflect "previously
crossed device", while following the path:

eth0 -> bond0 -> br0.

First step inside loop:

orig_dev = eth0
skb->dev = bond0 (at the end of the loop).

Second step inside loop:

orig_dev = bond0
skb->dev = br0 (et the end of the loop).

This would allow for exact match delivery to bond0 if someone bind there.

quoted

+
 	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);
-	}

I like the fact that it removes the above part.

quoted

+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;

Inside the loop, we should only do exact match delivery, for
&ptype_all and for &ptype_base[ntohs(type) & PTYPE_HASH_MASK]:

       list_for_each_entry_rcu(ptype, &ptype_all, list) {
-               if (!ptype->dev || ptype->dev == dev) {
+               if (ptype->dev == dev) {
                       if (pt_prev)
                               ret = deliver_skb(skb, pt_prev, orig_dev);
                       pt_prev = ptype;
               }
       }


       list_for_each_entry_rcu(ptype,
                       &ptype_base[ntohs(type) & PTYPE_HASH_MASK], list) {
               if (ptype->type == type &&
-                   (ptype->dev == null_or_dev || ptype->dev == skb->dev)) {
+                   (ptype->dev == skb->dev)) {
                       if (pt_prev)
                               ret = deliver_skb(skb, pt_prev, orig_dev);
                       pt_prev = ptype;
               }
       }

After leaving the loop, we can do wilcard delivery, if skb is not NULL.

       list_for_each_entry_rcu(ptype, &ptype_all, list) {
-               if (!ptype->dev || ptype->dev == dev) {
+               if (!ptype->dev) {
                       if (pt_prev)
                               ret = deliver_skb(skb, pt_prev, orig_dev);
                       pt_prev = ptype;
              }
       }


       list_for_each_entry_rcu(ptype,
                       &ptype_base[ntohs(type) & PTYPE_HASH_MASK], list) {
-               if (ptype->type == type &&
-                   (ptype->dev == null_or_dev || ptype->dev == skb->dev)) {
+		if (ptype->type == type && !ptype->dev) {
                       if (pt_prev)
                               ret = deliver_skb(skb, pt_prev, orig_dev);
                       pt_prev = ptype;
               }
       }

This would reduce the number of tests inside the
list_for_each_entry_rcu() loops. And because we match only ptype->dev
== dev inside the loop and !ptype->dev outside the loop, this should
avoid duplicate delivery.

Would you care to put this into patch so I can see the whole picture?
Thanks.