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

[Jiri Pirko <jpirko@redhat.com>]

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 :
>>Sat, Feb 19, 2011 at 12:08:31PM CET, jpirko@redhat.com wrote:
>>>Sat, Feb 19, 2011 at 11:56:23AM CET, nicolas.2p.debian@gmail.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@redhat.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;
>
>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.