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

From: Nicolas de Pesloüan<[email-masked]>
Date: Sat, 19 Feb 2011 21:27:37 +0100

Le 19/02/2011 14:46, Jiri Pirko a écrit :
> Sat, Feb 19, 2011 at 02:18:00PM CET, [email-masked] wrote:
>> Le 19/02/2011 12:28, Jiri Pirko a écrit :
>>> Sat, Feb 19, 2011 at 12:08:31PM CET, [email-masked] wrote:
>>>> Sat, Feb 19, 2011 at 11:56:23AM CET, [email-masked] 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<[email-masked]>
>>>>>>
>>>>>> 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.
>>
>>> +
>>>   	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.
>>
>>> +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