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Date: Sun, 20 Feb 2011 16:07:14 +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,
"Fischer, Anna" <anna.fischer@...com>
Subject: Re: [patch net-next-2.6 V3] net: convert bonding to use rx_handler
Sun, Feb 20, 2011 at 01:12:01PM CET, nicolas.2p.debian@...il.com wrote:
>Le 20/02/2011 11:36, Jiri Pirko a écrit :
>>Sat, Feb 19, 2011 at 09:27:37PM CET, nicolas.2p.debian@...il.com wrote:
>>>Le 19/02/2011 14:46, Jiri Pirko a écrit :
>>>>Sat, Feb 19, 2011 at 02:18:00PM CET, nicolas.2p.debian@...il.com wrote:
>>>>>Le 19/02/2011 12:28, Jiri Pirko a écrit :
>>>>>>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;
>>>>>
>>>>>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;
>>orig_dev should be set at the end of the loop. Now you are going to have
>>it always the same as dev and skb->dev.
>>
>
>Yes, you are right.
>
>I thinking about all this, I wonder what the protocol handlers expect as the orig_dev value ?
>
>Lest imagine the following configuration: eth0 -> bond0 -> br0.
>
>What does a protocol handler listening on br0 expect for orig_dev ?
>bond0 or eth0 ? Current implementation give eth0, but I think bond0
>should be the right value, for proper nesting.
I agree with you.
>
>>> 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;
>>>+ }
>>>+ }
>>
>>I'm not sure it is ok to deliver ptype_base here. See comment above
>>ptype_head() (I'm not sure I understand that correctly)
>
>Anyway, all this is probably plain wrong: Delivering the skb to
>protocol handlers while still changing the skb is guaranteed to cause
>strange behaviors.
>
>If we want to be able to deliver the skb to different protocol
>handlers and give all of them the right values for dev->skb and
>orig_dev (or previous_dev), we might end up with copying the skb. I
>hate the idea, but currently can't find a cleaner way to do so.
That would be unfortunate :/
>
>We first need to clarify what orig_dev should be, as stated above.
>
>>>+
>>>+ /*
>>>+ * 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.
>>Well this is not true. They can return NULL and call netif_rx as they
>>have before. No changes necessary I believe.
>
>I don't really know. This needs to be double checked, anyway.
>
>>>+ */
>>>+
>>> 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.
>>I'm not sure it is doable atm. For bridge and bond it should not be a
>>problem, but for macvlan, there is possible to have macvlans and vlans
>>on the same dev. This possibility should persist.
>>/me scratches head on the idea to have multiple rx_handlers although it
>>was his original idea....
>
>I think your original proposal of having several rx_handlers per device was right.
>
>At the time you introduced the rx_handler system, only bridge and
>macvlan used it. Even if using bridge and macvlan on the same base
>device might be useless, this is not true for every possible
>rx_handler configuration.
>
>Now that we want to move bonding and vlan to the rx_handler system,
>it becomes obvious that we need several rx_handlers per device. At
>least, vlan should properly mix with bridge. And who know what would
>be the fifth rx_handler...
>
>>>+ */
>>>+
>>> 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?
>>This hook is something I do not like at all :/ But anyway if should be in vlan
>>part I think.
>
>Yes, and in order for the future rx_handler for vlan to properly
>handle it, it needs to know the device just below it, not the pure
>original device. Hence, my question about the exact meaning of
>orig_dev...
>
> Nicolas.
>
>>>+ */
>>>+
>>> 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
>>>
>>>
>>>
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