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

Le 19/02/2011 14:46, Jiri Pirko a écrit :

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

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

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

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

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

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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.

Here is what I have in mind. It is based on your previous DRAFT patch, and don't modify rx_handlers yet.

Only compile tested !!

I don't know if every pieces are at the right place. I wonder what to do with CONFIG_NET_CLS_ACT 
part, that currently is between ptype_all and ptype_base processing.

Anyway, the general idea is there.

	Nicolas.

  net/core/dev.c |   70 ++++++++++++++++++++++++++++++++++++++++++++++++--------
  1 files changed, 60 insertions(+), 10 deletions(-)

diff --git a/net/core/dev.c b/net/core/dev.c
index e5dba47..7e007a9 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c

@@ -3117,7 +3117,6 @@ static int __netif_receive_skb(struct sk_buff *skb)
  	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;
  	__be16 type;

@@ -3130,9 +3129,6 @@ static int __netif_receive_skb(struct sk_buff *skb)
  	if (netpoll_receive_skb(skb))
  		return NET_RX_DROP;

-	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;

@@ -3143,6 +3139,8 @@ static int __netif_receive_skb(struct sk_buff *skb)

  another_round:
  	__this_cpu_inc(softnet_data.processed);
+	skb->skb_iif = skb->dev->ifindex;
+	orig_dev = skb->dev;
  	dev = skb->dev;

  #ifdef CONFIG_NET_CLS_ACT

@@ -3152,8 +3150,13 @@ another_round:
  	}
  #endif

+	/*
+	 * Deliver to ptype_all protocol handlers that match current dev.
+	 * This happens before rx_handler is given a chance to change skb->dev.
+	 */
+
  	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;

@@ -3167,6 +3170,31 @@ another_round:
  ncls:
  #endif

+	/*
+	 * Deliver to ptype_base protocol handlers that match current dev.
+	 * This happens before rx_handler is given a chance to change skb->dev.
+	 */
+
+	type = skb->protocol;
+	list_for_each_entry_rcu(ptype,
+			&ptype_base[ntohs(type) & PTYPE_HASH_MASK], list) {
+		if (ptype->type == type && ptype->dev == skb->dev) {
+			if (pt_prev)
+				ret = deliver_skb(skb, pt_prev, orig_dev);
+			pt_prev = ptype;
+		}
+	}
+
+	/*
+	 * Call rx_handler for current device.
+	 * If rx_handler return NULL, skip wilcard protocol handler delivery.
+	 * Else, if skb->dev changed, restart the whole delivery process, to
+	 * allow for device nesting.
+	 *
+	 * Warning:
+	 * rx_handlers must kfree_skb(skb) if they return NULL.
+	 */
+
  	rx_handler = rcu_dereference(dev->rx_handler);
  	if (rx_handler) {
  		if (pt_prev) {

@@ -3176,10 +3204,15 @@ ncls:
  		skb = rx_handler(skb);
  		if (!skb)
  			goto out;
-		if (dev != skb->dev)
+		if (skb->dev != dev)
  			goto another_round;
  	}

+	/*
+	 * FIXME: The part below should use rx_handler instead of being hard
+	 * coded here.
+	 */
+
  	if (vlan_tx_tag_present(skb)) {
  		if (pt_prev) {
  			ret = deliver_skb(skb, pt_prev, orig_dev);

@@ -3192,16 +3225,33 @@ ncls:
  			goto out;
  	}

+	/*
+	 * FIXME: Can't this be moved into the rx_handler for bonding,
+	 * or into a futur rx_handler for vlan?
+	 */
+
  	vlan_on_bond_hook(skb);

-	/* deliver only exact match when indicated */
-	null_or_dev = skb->deliver_no_wcard ? skb->dev : NULL;
+	/*
+	 * Deliver to wildcard ptype_all protocol handlers.
+	 */
+
+	list_for_each_entry_rcu(ptype, &ptype_all, list) {
+		if (!ptype->dev) {
+			if (pt_prev)
+				ret = deliver_skb(skb, pt_prev, orig_dev);
+			pt_prev = ptype;
+		}
+	}
+
+	/*
+	 * Deliver to wildcard ptype_all protocol handlers.
+	 */

  	type = skb->protocol;
  	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;

-- 
1.7.2.3